ESE's works engine tuner

[Yow Ling]

Post Classic possibility for the Tiddler class.

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One cylinder of a RG125T bore stroke 43x43, 44 crank hp as a twin.

What is an rg125t ?

[ief]

Perhaps it is as simple as, the one that gives most power Rob, sance detonation :) Let's see what Wob says. I just used a 4 point curve like I know from rd's and the like, felt more comfortable, eager to see if your efforts where the right way.

edit: cooling might be easier with 'mine' in the longer run?

ps, you think the rs125 scavenging is apropriate for the/ your RG?

[TZ350]

What is an rg125t ?

Home brew Suzuki GT125 twin fitted with RG50 cylinders that have been bored for 62cc each.


ps, you think the rs125 scavenging is apropriate for the/ your RG?

No not sure, but the RG50 has reasonably curved transfer ducts. I usually use Yam12 for the GP but non to sure if that is the right thing to do either.

[ief]

That I'd never tried this before... rs125 vs yam12, hardly a difference (on this setup) Was expecting something major :)

[wobbly]

TubMax is a reflection of the % of fuel energy retained in the unburned end gases trapped in the squishband.
The shape of this curve is affected by a myriad of elements but the biggest factor is the real ignition timing.
In a race engine the results are supremely useful for juggling the ignition timing to fix any major anomalies that can produce low bmep
at one point or several in the usable powerband.
Where you are running what i would call "normal" numbers for timing - say 28* at the bottom of the range and 15* at peak then some further retard
to get heat in the pipe for overev capability,the curve shape will be close to that of the torque produced, a flattened bell.
ie low 900 rising to high 900*C at peak torque then dropping away again as more of the combustion heat energy is dumped into the pipe.
You have to be careful of part throttle deto at the beginning of the powerband, and then of course if the temp starts hovering at 1000* in the high power range
you will get DETO lighting up on the screen.
To drop the temp it is easy enough to simply retard the timing - but more power may often be had by adjusting the stinger, or reducing the com/squish velocity then rerunning the
Turbulent model to account for the differing flame propagation speed thru the chamber due to squish turbulence changing the combustion delay numbers etc.
These factors are just as important, sometimes more - than the "raw" ignition timing number at any rpm point.
Each end of the bell curve can be tipped, by use of a powervalve for example,or a solenoid powerjet that is simulated by a change in A/F ratio past peak power.

[F5 Dave]

Suzuki GT125 twin fitted with RG50 cylinders that have been bored for 62cc each. . .
Making a 125 wc 2 stroke. What class will you run that?

[TZ350]

Thanks Wob ...

[TZ350]

Making a 125 wc 2 stroke. What class will you run that?

A friend is looking at Post Classic Tiddlers, but it has got me thinking about a 100cc version, maybe if the RG50 project goes well we will make a 100cc twin with CVT for F4.

[F5 Dave]

A friend is looking at Post Classic Tiddlers, but it has got me thinking about a 100cc version, maybe with CVT for F4.
Will only be legal if you can prove it was done at the time. Which considering the RG was released in about 1984 might require Marty McFly to be involved (think DeLorean)

Ahh screw the infringements, Win8 makes this too hard.

http://my50.co.za/wp-content/uploads/2013/06/1985-Suzuki-RG-50-Gamma-Yellow-980x500.jpg



I googled Suzuki RG50 for images & a few rows down saw myself on my No. 27 RG when it was silver.

[TZ350]

306390

F5Dave ......

[F5 Dave]

The oddities of Google. I ran it again & it didn't show. Then I refreshed & refreshed & it did. Lage size, note Flag guy in the 'Bum pants' we awarded if you fell off. Had to wear them till someone else fell off. This isn't posed photo, I look bored. Those leathers look 10 years newer than now.

http://www.motorcycleparts.co.nz/teambuck/dt-rg50-2003-kaitoke2.jpg

[jasonu]

Home brew Suzuki GT125 twin fitted with RG50 cylinders that have been bored for 62cc each.
.

Please post pictures.

[TZ350]

Will only be legal if you can prove it was done at the time.

Yes you are right, not pre 82 at all, ohoo well it could make a neat F4 100 I suppose.


Please post pictures.

No pictures, its just ideas at the moment, and anyway the cylinder spacing of the GT125 is a bit tight for two RG50 cylinders. We would have to shave the inside sides of the RG50 cylinders to get them to fit, could be done but does not look easy.

[F5 Dave]

Its been done with 2 watercooled MB50 cylinders by Phil Bird. Actually GPR own it for last 20 yrs

I've looked at RG cases & wondered about a Vtwin conversion that might just fit in the RS chassis. Would be light for a twin which the GT isn't + GT is 5 speed.

[husaberg]

A friend is looking at Post Classic Tiddlers, but it has got me thinking about a 100cc version, maybe if the RG50 project goes well we will make a 100cc twin with CVT for F4.

but you wouldn't use a old 1980's rg50 cylinder would you...........its 2014. I wrote 2013 first time lol:killingme

[TZ350]

Its been done with 2 watercooled MB50 cylinders by Phil Bird. Actually GPR own it for last 20 yrs

Yes, I have seen pictures of it somewhere that Scott posted a while back.


I've looked at RG cases & wondered about a Vtwin conversion that might just fit in the RS chassis. Would be light for a twin which the GT isn't + GT is 5 speed.

RG V twin .... :scratch:that could be possible, light, good gearbox.

Heavy 5 speed GT, thats why I thought it might be a good candidate for cutting the gear box off and making a CVT out of it.

[husaberg]

Yes, I have seen pictures of it somewhere that Scott posted a while back.



RG V twin .... :scratch:that could be possible, light good gearbox.

Heavy 5 speed GT, thats why I thought it might be a good candidate for cutting the gear box off and making a CVT out of it.

..............................

[ief]

Perhaps a daft question but wondering none the less. As far as I understand, given the right input, engmod outcome resembles reality pretty good, couple % off maybe? Does that mean the same goes for the exhaust? Logic tells me it is since it's part of the sim but still....

[wobbly]

A huge part of Neels efforts to recreate reality in the sim results is all around the code needed to model the wave action within the pipe.
A 2T lives and dies on the correct timing and amplitude of the particle flow down the pipe, much as a 4T lives and dies on the intake tracts influence.
The latest code change that now has an accurate model of the actual wall temps effects has got the results even closer, without the demon fudge
factors Neels hates with a passion.
The only caveat i would add is that there is still some leeway for idiocy to creep in, and still get a result that seems fine ie 25* diffuser angles.
Go back to the old texts and you will find that very early on in the development of expansion chambers it was found that the angle that gave the best
energy recovery ( amplitude Vs period ) of the depression communicated to the Ex port during the scavenging phase was 16* included.
This is now modified somewhat in that we can and do have up to 6 different cones, all interacting and changing the shape of the negative pressure ratio plot
as seen at the port face when the piston is around BDC, but as is human nature we always think more must be better - even with single malts.
Just keep in mind that any energy used in the diffuser,must then reduce the energy available to be used in the reflection phase - there is only a finite ( and ever decreasing )
energy level available that starts when the piston cracks open the port.

[Flettner]

Wobbly, I assume no Mallory news is bad news?

[TZ350]

... you wouldn't use old 1980's rg50 cylinders would you...........its 2014.

No, maybe not for a CVT 100 twin project, if they were legal for Bucket racing I would prefer the KTM 50 cylinder.

But for our Team ESE F5 racing class 50's we want to use the old school RG50 cylinders/engines precisely because they are from the 80's (and we have collected a few of them, so cheap to start with).

Chambers has been working on a RG50 engine/RS chassis bike for Av. It is currently making 13.5+ rwhp using an original old style single exhaust port RG50 cylinder from the 80's.

Back in the day, we think the norm for the old school Bucket (F5) racing RG50 was 10-11 rwhp so just for the fun of it we want to see how far we can get with them, the ambition is 16-17 rwhp and to show that the humble 1980's RG50 can be more than a match for the newer, more expensive Aprilia and Derbi 50 motors with their aftermarket cylinders.

306422306424

And it looks like the old 1980's RG50 engine is still being used in the newer RMX 50's.

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So still plenty of engine parts available.

And even aftermarket cylinders if you want to go there, but for now, we don't think we will have to, to do better than the current Aprilia and Derbi engines.

306427

With the right sort of (thin deep) ring(s) 50's can run with quite wide (80%+) exhaust ports so you could probably make much more power if you can get away with cutting the bridge out and running it as a single port. If these aftermarket cylinders are legal for F5 racing, then one day we might get one of them to see what can be done, maybe a 20 rwhp RG50 is possible.

I have brought OKO carbs from these guys at Treatland before, https://www.treatland.tv/ even visited them a couple of times, I have found them to be great to deal with.

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https://www.treatland.tv/OKO-26mm-reed-block-intake-for-DIO-BLK-BLK-p/oko-dio-reed-block-105.htm

I have been looking at this Honda Dio reed block and manifold they sell with the view of cutting the reed block manifold and welding it into the back of an RG50 cylinder for an easy reed valve conversion. The rubber manifolds suit the OKO 21-24-26-28-30mm range of carburettors.

Wobbly is working on a RG50 project for Gigglebutton, so there could be a few fast RG50's out there next season.

[TZ350]

<iframe width="560" height="315" src="//www.youtube.com/embed/q5zzWtj84VY" frameborder="0" allowfullscreen></iframe>

Fun things to do with a 150cc BSG cylinder.

<iframe width="560" height="315" src="//www.youtube.com/embed/FG8apE4d2FI" frameborder="0" allowfullscreen></iframe>

[peewee]

Where you have an angled exit on one wall like that I use a combination of the flow and chordal width.
In reality the port flow area will be very close to the chordal width, as when the flow exits the duct its effective area
will be less than a straight flow port, but more than the flow area measured vertically as you have drawn it.
In between approximation is the chordal width as i have shown.

i got molds of the original ducts today and im going to make it so theres a radius turn instead of a sharper hook. what do you think about the flow width on the A ? as you can see from the orange and green arrows, the flow width will vary alot depending on which wall you calculate from.
if i use the front wall i get 20mm flow width. if i use the rear wall i get 27mm

[TZ350]

306457

Hi PeeWee I am interested in this too, so what size coin fits in there? and didn't Wob talk about the chordal width being a suitable measurement? It looks like the 20mm green line to me. The moulds look good.

[peewee]

yes he said chordal on the B but the A doesnt seem to be that simple however because of the angle of either wall into the cylinder. a true chordal on the A port would be more like the purple line. thats why im confused on this. was my first time making the molds. gonna try a release agent next time as it was a bugger getting them out of the ducts. grill is useful more than just food :bleh:

[peewee]

well after looking again, the purple line (chordal) and green line are about the same at nearly 27mm width. the orange line however is alot smaller at 20mm. the B port was 20mm also. it doesnt seem right that both A and B would be the same when the A window is alot wider chordially than B but its the angle that A enters the cylinder that makes it confusing. seems like i should use the green line but i dont know.

[peewee]

ok ill use the green line as that seems to make the most sense to me

[TZ350]

... this was my first time making the molds. gonna try a release agent next time as it was a bugger getting them out of the ducts. grill is useful more than just food :bleh:

I like the grill idea.

[peewee]

grill worked pretty good. cost me almost nothing since i already had it on the back porch. bought a metal pan from walmart for $10. has a thermometer in the lid. set the dial to maintain 275-300F. took about 15-20min and it was melted perfect and ready to pour in the cylinder :cool:

[jasonu]

..............................

What is this bike Husa?

[wobbly]

As Neels says you have to use some judgement to get the actual flow width correct.
Using the example he gives in the help file, if we call the bottom port an A port with a heavily sloping front wall, the flow width will be very close
to the original flow width as he drew it .
If we call the top port a B port with a hook, its effective flow width will be very close to the chordal as he drew it.
The A port may in fact be much wider chordally, but because of the entry geometry the actual flow thru that port will be reduced by the cosine
of the entry angles - exactly the same as the software reduces the effective area by the cosine of the axial upward angle of the duct.
Where there are two distinct entry angles, use your judgement to get what would be the real flow width.

[peewee]

wobbly how did you go about calculating the entrance ? the engmod help file doesnt seem to be real specific about this.

did you just use chordal width x height from case to cylinder sleeve, like the green arrow ?

or did you use something more like a flow width as the red arrows show. red arrow A + red arrow B x height of case to cylinder sleeve ?

[peewee]

actually if you used a chordal width you would probly do something more like this , with the opening width split into 2 parts to give designation for the A port and B port. then simply green arrow A x height. green arrow B x height

[wobbly]

Depends upon the cylinder design.
In the case of the Yamaha you are working on the septum divider is very tapered, so the effective entry area is pretty much as you say for each port - the two green arrows times the height.
But in an Aprilia where the septum is very wide, the effective duct acts much more like the angled flow widths times the height.
Then there is the extra entry coefficient added by the shape of the inner bore wall.
The length is the important factor, the entry area/exit area ratio does not make a big difference at all, except where you do not have the transfer duct volumes as part of a measured input.
I recently ran a test on this out of interest - with everything kept constant ( including the case vol ) having a 1:1 entry/exit ratio and a 1 :1.5 ratio made virtually no difference.
This ties in with my assertion that all of the mixture transferred into the cylinder is sitting in the ducts, there is no actual flow from the case into the cylinder when the transfers are open.

[Grumph]

This ties in with my assertion that all of the mixture transferred into the cylinder is sitting in the ducts, there is no actual flow from the case into the cylinder when the transfers are open.

I don't disagree with you....How do you see the classic MZ style 3rd transfer at the rear fed by a window in the piston ? Is this the exception ?
Is it worth looking at Joe Ehrlich's boost ports again - if room can be found for them ?

[husaberg]

What is this bike Husa?

Its been done with 2 watercooled MB50 cylinders by Phil Bird. Actually GPR own it for last 20 yrs

I've looked at RG cases & wondered about a Vtwin conversion that might just fit in the RS chassis. Would be light for a twin which the GT isn't + GT is 5 speed.


Yes, I have seen pictures of it somewhere that Scott posted a while back.



RG V twin .... :scratch:that could be possible, light, good gearbox.

Heavy 5 speed GT, thats why I thought it might be a good candidate for cutting the gear box off and making a CVT out of it.
Gpr100
Suzuki GT125 bottom end modded MB50 cylinders water cooled engine made by...(dave or mike mentioned it) Phil Bird

[wobbly]

The duct length is very short in the MZ style thru the piston feed entry, but this is probably offset by the fact that the axial angle is so steep the
effective area at the bore is tiny - thus the actual flow cc is tiny as well..
But even that small duct has to be filled from somewhere, and the hole in piston,into the duct works well compared to non at all.
I worked at EMC building pipes in the early days of the Rotax 256 , and the idea of a hole in the piston, lining up with a hole in the boost port duct made a couple of Hp in the twin.
We tried doing the same thing with all the transfers, spending hours grinding holes in the bores, but sadly this made less power.
Later on in the Rotax development it was worked out that the boost duct entry was badly shrouded, and once this was fixed along with a 1/2 moon cutaway in the piston skirt
was introduced, power went up another couple of Hp over the hole in piston idea.
Joe's boost ports were a quick fix for crap scavenging in a piston port, and really were just a band aid - but as he was very good at ,Yamaha paid a fortune to him for the idea to be used in
the twin 125 Yamaha that really was a very good little engine in its time.
Yamaha paid Joe another fortune for the dumb offset combustion chamber patent, that only got into production for 1 year in a TZ.
Then they finally realised that having no squish on one side, and huge squish velocity on the other ,actually caused detonation - someone at Yamaha Corp must have felt really stupid/and or got fired.
But Dr Joe went laughing all the way to the bank - then started taking loads of cash from USA outboard people, again mostly bullshit technology, but hey I dont want to overly deride those
that taught a young Kiwi plenty about the workings of a racing 2T.

[senso]

Wobbly, one question regarding the transfer ducts sizing, you say/have discovered that the relation between the entry and exit areas is not a critical value, but what about the ducts volume, since the engine only charges the cylinder with what is available in the ducts, having small ducts with reduce volume can limit the engine total power?

Being more specific, I have a 54x43mm cylinder(yes I know, its over-square as hell, but to mitigate that I will use a 45mm stroke), that cylinder has a total volume of 84cc in the ducts of the A and B transfers, being the C feed directly from the reed-cage intake.
I usually make then a bit bigger, but much because there is only 4mm of aluminium to seal the cylinder against the crankcase, but enlarging them makes the duct outer walls practically vertical, what would be better, to have a bit more volume to feed the 100cc cylinder or try to maintain the curvature?

The boyessen ports are also tiny, I can only bore them to 6mm, more than that must be made oval.

Some pictures to make the question more clear:

[wobbly]

When I said that the length is the important factor, not the in/out area ratio, I should also have added that the duct shape that sets the scavenging
efficiency of the port combinations more important than even the length.
The duct length in the sim includes the area below the cylinder deck, so in reality the volume you quote will be way bigger than the swept volume.
So to answer the question,keep the curvature and make the Boyesen ports oval to ensure you dont start to become intake area limited with the bigger cc
as well as the higher bmep.

[F5 Dave]

Back to the 256 shrouding issue, I've ended up reversing my skirt (ooer) for more support (I went from having virtually no skirt with centre cut out and mooned piston to full piston & centre protrusion). But I've got the stub in the middle, I guess if I'm charitable like an RS Honda. Case reed mod to MB100.

this lightly encroaches into the reedblock stream but so be it. The Boost entry is now filled in on both sides from this picture, but it is shrouded from the centre to the duct, but not from the reed as much (but with 90*turn). The Rotax being rotary valve I guess this would be an issue more than a case reed valve? Or should I be looking at a hole?

[TZ350]

306528

What an 85% RG50 exhaust port looks like.

We are in untried territory now, I have some new pistons coming, and it will be interesting to see how the extra 5% goes.

Timing, Ex opens 84 atdc, Trans open 121 atdc and as wide as possible, In opens 90 btdc with Suzuki case reed.

[F5 Dave]

Better put a real careful chamfer on that and smooth it super well. Even then the piston might pop out the port every 2nd revolution and up the bore alternate ones. Maybe you've created a four stroke?

[jonny quest]

I recently did some dyno testing on a newer Yamaha YZ125. They have a hybrid type flat top piston with a 12 degree angle about 3mm wide on perimeter with head to match.

I installed a dome piston with exact same edge height, modified a head to RSA style to match the dome, and used same compression ratio as flat top setup (15.5:1).

The stock flat top made a full 1 hp more. The only advantage dome setup had was a flatter peak curve.

Both pistons were cast OEM variety, the domed piston was from a CR125 (very similar to RS125).

Just curious if anyone has found more power with a flat top piston?

[TZ350]

Better put a real careful chamfer on that and smooth it super well. Even then the piston might pop out the port every 2nd revolution and up the bore alternate ones. Maybe you've created a four stroke?

306535

I am hopeful it won't behave like a typical four stroke and shit itself, never the less I won't be standing to close when it gets run up for the first time on the dyno.

[F5 Dave]

If it survives pull the head off and check for scratches above the port. Uncharted waters but certainly got the area mine was begging for but I was only game to push 75%. Spend some time. I have a cigarette oilstone for final smoothing but you'll need to go hard to start with, its sharp as pictured.

[wobbly]

The hybrid design was done for the TZ and YZR designs when Yamaha got themselves a CNC anemometric flow visualising machine.
Nakanos and Jaques TZ250s were so superior using the newly developed cylinders and pistons they were easily 1st and 2nd in the GP champs
after the TZ being severely blown away for years by Honda and Aprilia.
They obviously used that shape for a reason, imho that approach is probably the best for flow attachment to the piston and least heat soak area.
But yes I have done back to back dyno testing with A Kit Honda parts and in the end a flat top with a proper toroid made better power than the dome
and a bathtub as developed at Aprilia by Jan.
When pushed right to the edge with deto, a flat top wins in that when the dome collapses it does not trap the ring immediately as happens with the curved shape.
The latest developments in KZ2 karts has the dome changing from a 7* conic to a 4*, and just now we learn that VHM have been testing a flat top CNC billet piston
and have published a graph showing around 0.9 Hp advantage on the dyno.
Remains to be seen if the lack of transfer flow attachment, cooling the piston, actually is an issue in a 25 lap final.
Years ago we raced Pavesi 125 engines with flat top designs and at the time they were renowned for making great top end power with no more problems with deto
than the others with curved pistons.
But where the extra power came from I will never know as they refused all my attempts at getting them to increase the reverse transfer stagger, and double the size of the Aux Ex ports.
If they had they would have been just as fast as the Maxter and TM engines are now - 10 years later,47Hp instead of 42.

[F5 Dave]

Bumpity? .


Back to the 256 shrouding issue, I've ended up reversing my skirt (ooer) for more support (I went from having virtually no skirt with centre cut out and mooned piston to full piston & centre protrusion). But I've got the stub in the middle, I guess if I'm charitable like an RS Honda. Case reed mod to MB100.

this lightly encroaches into the reedblock stream but so be it. The Boost entry is now filled in on both sides from this picture, but it is shrouded from the centre to the duct, but not from the reed as much (but with 90*turn). The Rotax being rotary valve I guess this would be an issue more than a case reed valve? Or should I be looking at a hole?

[wobbly]

The 256 had an issue with smashing off the rear cylinder spigot as soon as piston clearance became even slightly loose - due to the skirt and boost cutaway
not giving much support to the bdc piston rock.
Most cylinder reeds have problems with the reed stops shrouding the boost entry, so as long as this isnt an issue ( maybe fit a reed spacer )
then I would say its fine - can you pic inside the reed box for a better view.

[senso]

When I do simple engines just to spice them up a bit, and given that they have a cylinder reed intake I just grind or cut the reed stops a bit(usually about 4-6mm) so the boost port is a bit less shrouded, its cheaper than making a spacer.

[jonny quest]

Good info Wobbly on pistons, thanks.

Wonder why RSA ran the domed piston? Frits? Ignition, triple port instead of bridge?

[richban]

I question for those in the know.

I need to really be cranking out of the corners on track. ( I'm getting smoked by the thumpers ) so I am planing to push the gearing on the bike so its in 6th and in over rev at the end of the big long straight. Sacrifice a little top end, for max corner exit speed. What I want to know is what is happing in the combustion chamber when the bike is reving at 12k but out of its happy place. My bike does have very good over rev. It does not drop off that bad. Peak power is just under 11 and it is happy to rev to 12 with no major loss. What I want to know is. When in over rev is it lean or rich?

[husaberg]

That is true if you look at transfer flow. But from a cooling perspective, scavenging through the piston does help.

It might work, and it might help cool the piston. But at the same time it would raise the average temperature of the fresh charge, so it would be useful only if piston temperature is a limiting factor in that engine.

Theoretically, yes. But where should I put those holes? They must not run over the exhaust windows, which leaves only the areas fore and aft (the exhaust ports are on the right and left sides). But mid-fore and mid-aft there are no transfer ports because I reserved those areas for the piston to lean against, and for the ring gap.
The picture of the cut cylinder below shows the available areas for piston cooling windows in red. But I'm not sure whether I want to make four holes in a piston that will be very highly stressed once the rpm potential of the FOS porting system is fully exploited.


I have been working on that C port piston hole and proper transfer duct combo for direct cooling of the underside of the piston crown and would be interested in other peoples experiences with the idea too.


I don't disagree with you....How do you see the classic MZ style 3rd transfer at the rear fed by a window in the piston ? Is this the exception ?
Is it worth looking at Joe Ehrlich's boost ports again - if room can be found for them ?

I have never noticed this cylinder Nor do I know what variant it is, Anyone?
306581

[peewee]

Most cylinder reeds have problems with the reed stops shrouding the boost entry,
.

ive seen a few cylinders like this. some hondas. and even the banshee with a stock reed block which plugs off nearly the entire boost entry. funny thing is the vf4 block leaves the boost entry almost fully open. another problem ive found with some reed cylinders, the reed block is so long and the inlet so short, the outer corners of the block sit over top of the boyesen ports . mostly clogging them from normal function

on my honda i cut back the stoppers which uncovered the boost quit a bit. still the boyesens were partually clogged but without a spacer there wasnt much i could do about that

[husaberg]

I question for those in the know.

I need to really be cranking out of the corners on track. ( I'm getting smoked by the thumpers ) so I am planing to push the gearing on the bike so its in 6th and in over rev at the end of the big long straight. Sacrifice a little top end, for max corner exit speed. What I want to know is what is happing in the combustion chamber when the bike is reving at 12k but out of its happy place. My bike does have very good over rev. It does not drop off that bad. Peak power is just under 11 and it is happy to rev to 12 with no major loss. What I want to know is. When in over rev is it lean or rich?


When using a simple powerjet nozzle the tip position matters in that no flow will occur until the slide is well past the exit hole, and there is sufficient airflow
to drag fuel up the feed tube above the bowl level.
With the aftermarket add ons and the ones as used by Lectron you can shorten the dump tube so that the flow will only occur at high slide openings,as well as high air flow.
These also have a built in "lag "control in that it takes time for the fuel to rise up the tube and dump out the exit into the air stream.
With a solenoid controlled setup all this is pretty much irrelevant as the flow can only occur when the solenoid is not powered up, and this
is TPS as well as rpm dependant inside the ECU program..
The carbs as used on the MX bikes has the dump tube very low in the bore as they added and subtracted fuel at low slide positions in those bikes.
For a race engine I bend the tube up to around 1/2 bore, as this is where the exit is on the Kehin SPJ carb for RS125/RS250 Honda.
And the general setting is the solenoid is powered up ie no flow below 4000 and 60% TPS and is powered up again at around 12400 to lean off the mixture and increase revon.
This causes a problem with Ignitechs that are used with only a capacitor, as at startup the solenoid is powered up, dragging all the voltage out of the ECU, so I convert the ECU output
to a 3 step truth table, and have the setting such that below 1500rpm the solenoid isnt powered.


Aha, I see. I think I got it now, Frits.
If the powerjet is positioned in the middle of the venturi or at a lower point, that will affect how much it will flow, correct?

I remember both Lectron and Mikuni aftermarket PJ kits' instructions, saying that the end tip of the pj should be around the middle of the carb.
Yet the Keihin PJ of the carbs for the mx250 models is down low! Position would also affect which fraction of the flow becomes more rich or not, or that doesn't matter??

255006


254941

Made an adjustable PJ out of a model aero engine carb needle jet for controlling the PJ. Now to get one of those solenoids the Husaburg posted to shut off the PJ for a bit of extra over rev.

Made some progress with the shorter inlet tract and expect to get the lower mid range back again with a bit of fiddling with the carburation.

Just a little bit more and the single exhaust port engine with the RS pipe will be very close to EngMod2T's predicted power output.

254940 125cc rotary valve with a 24mm carb and air cooled.

Measured 31 rwhp (estimated 34 crank hp) on the dyno tonight, red line is last night before the inlet tract was shortened and the jetting/ignition adjusted.

I have ordered one of Wobblys special kitset "A" Kit Pipes for a Suzuki GP125 ..... so hopefully 1 or 2 more hp and a wider spread of power. Then there is the ATAC idea for better low end.


Nope. It is drawn by the dynamic pressure at the fuel exit points in the carburetter. And that pressure depends on the mean air flow velocity along those exits.
Air flow velocity is at its highest in the center of the narrowest part of the inlet tract, so the location of the fuel exit will make a difference. And by mean air flow I mean (air flow into the engine + backflow)/2.
You see, more than enough variables; more than enough differences between the exit points of the fuel flow through the main jet and the flow through the power jet.


Re the tiny bleed hole in the TZ powerjet tube - I always thought that this was a good idea to emulsify the fuel as it exited the dropper.
But years ago i did some wet tests on the flowbench with a VCR video camera ( pretty trick shit stuff back then ).
The Mikuni was a horror scene when played back slo mo,with huge "gobbs" of fuel exiting the main and powerjet.
We then stuck on a Lectron - wow, lovely fine mist of fuel from the back of the flat needle face - and it flowed 12% more air - size for size with a venturi 2mm smaller behind the slide.

Next is the current state of TeeZees GP125, here is the latest dyno curve digitised with 16% added to simulate crank power.
Then there is the sim with an actual RS early model pipe.
Then there is the new pipe of my design.
Of most interest is that in this case the sim is giving slightly too much crank power - but the shape and peak point are all but perfect.
I would be confident now that any change in the sim, would be reflected in reality on the dyno.
In my experience the later Dynojets like a twin roller 168 with Eddy current load control to slow the acceleration rate down ,seem to read around 5 to 10% lower
so this would put the sim and the dyno reading very close, as the shape is spot on now.


You have to be very carefull with the switch point and the run time on the dyno.
The switch point is dead critical to 100rpm,so i always set it too high initially and make sure that the dyno is loading the acceleration rate to be as close to that on track as you can.
This gives the pipe time to heat up and affect the power over the top, as it would in reality.
On a RS250 dropping the switch point from 12800 ( std) to 12400 gives easily another 800 rpm of virtually no power drop past peak.
On the track,if the rider can feel the switch point ( it feels like hooking another gear)the jet is too big,when its right it should be seamless and just keep reving out.
Leaded fuel is the opposite to unleaded, in that as leaded likes to run lean - you can only use a small powerjet and thus only switch off a small amount.
A leaded engine works best with around 35 to 38 PJ, the unleaded fuel can switch a 60, in Keihin numbering, as the crap fuel makes best power at peak when quite rich..


And something that I scraped from the net.........

""The solenoid control on TZ type powerjets really just shuts off fuel flow to the powerjets right at the top of the rev range to lean the mixture off to increase the over-rev once you are past peak power.

I don't have the solenoids plugged in currently though as I find they work well enough for my current needs with the powerjets simply responding to venturi vacuum pressure in pretty much the same way as the oem 3MA powerjets work.""

233787233788

And here is a picture of the carbs and what I can make out, a dyno graph without, and with the power jet solenoids shutting off (red line) and extending the over rev.

So it looks like you can use an electric power jet like a standard one and when the carburation is sorted, try switching it of by activating the solenoid at or just after peak power and see what happens with the over rev.


The FPE superkart engine that won the NZ road title at Manfield a few weeks ago makes 92 RWHp on the Dynojet 168 I use.
Still not quite as good as the RS250 setup we did that won at Laguna Superkart Worlds a couple of years ago.

The powerjet carb is controlled by the Ignitech with a combination of throttle position and rpm in a "truth table".
In general the solenoid is activated with 12V ( no fuel flowing) below 4000 rpm and 75% throttle on the TPS.
Above 75% and around 12400 rpm it is activated again to lean off the fuel curve over the top of the pipe.
Looks like you will be able to reverse the fuel exit, blocking off the hole on the throttle bore side, and take off fuel from the outside bung, thru a needle jet and into the top of the venturi next to the slide.


Recently I got myself (Ebay) a 38mm carb with Throttle PS and Electric PJ from a motor crosser.

Wobbly told me that on those the PJ nozzel is to low and starts to flow to soon for a road racer and the MX ones are hard to tune.

230481

I couldn't afford to buy a good second hand TZ or RS unit. So I figure that moving the discharge nozzel.

230483

And adding an adjustable jet from a large model aero engine could be worth a try.

230482

On the dyno I have seen how a leaner mixture rev's on further and how richining it up for best power the over rev drops off.

I think that as the rpm goes up the mixture strength on an ordanery carb at max rpm goes over rich.

And at the moment I think the idea is that the PV is shutoff after peak power to get back to the correct mixture and by retarding the ignition at the same time extend the over rev, but I am sure there is more to it.

I would love to know more about how this type of carb should be used and/or setup.



The modern take on powerjets is to turn them off after peak power to extend the rev range. This assumes that you are happy for your engine to rev that much further past peak power & on many buckets perhaps this is not so good unless you have uprated the crank assembly. The jet will start to flow, depending on its position. Some don't seem to work well without an airbox if they aren't very prominant, or perhaps if the suction isn't so much (putting big carb on a smaller cylinder). In some cases they are best blocked off presumably if the air jet doesn't match very well & is tending to increasing richening with airflow as it is.


With all the talk about wanting to utilize only a couple of gear changes per lap, I would have thought that the solenoid powerjet was a gift from heaven.
A late model well tuned RS125 will rev to around 12400 if the PJ is disabled,turn the PJ function back on and it will go to 13800+.
Its so simple and you retain exactly the same lower rev power,but with easily another 1000rpm to work with you have the choice of adding teeth on the back, getting better acceleration from torque multiplication, or keeping the same gears - but increasing the terminal speed.
And from the dyno curves I have seen, most of the 100 buckets with short stroke lengths, arent even beginning to stress the bottom ends - with less peak rpm than the 54.5mm stroke 125 bikes or karts that will easily run to 13000 all day.



Some more RSA125 development info from Jan Thiel

"No pressure transducers were ever used in our engine development.
And time/aerea was never calculated.
The port timings remained practically the same during 15 years!
What we did was trying different angles and radiuses, mainly on
the transfer ducts. I think we tried 40 different types of transfer ducts
that did not chanche the time/aerea. It was all about in which direction
the charge entered the cilinder and how the tranfer streams influenced upon
each other! Also about 200 different exhaust pipes were tried. After 2004
nothing much was changed but we improved with different power jet and
ignition mapping. It seemed nearly impossible to improve the transfer ducts
any more. The exhaust ducts were CNC machined, using different programs,
mainly to reduce exhaust duct volume. Also about 100 head designs were tried"

Didnt calculate time area? Im guessing that means the time area requirement hasnt changed any in the last 15+ years.
So there you go its all about the transfer ducts, now where have I heard that before?
Check out the attached photos, I guess the idea of thinning the transfer duct bridge has gone out the window, and the exhaust duct hows that for a crazy shape


231454
231455
231456


Recently I got myself (Ebay) a 38mm carb with Throttle PS and Electric PJ from a motor crosser.

Wobbly told me that on those the PJ nozzel is to low and starts to flow to soon for a road racer and the MX ones are hard to tune.

230481

I couldn't afford to buy a good second hand TZ or RS unit. So I figure that moving the discharge nozzel.

230483

And adding an adjustable jet from a large model aero engine could be worth a try.

230482

On the dyno I have seen how a leaner mixture rev's on further and how richining it up for best power the over rev drops off.

I think that as the rpm goes up the mixture strength on an ordanery carb at max rpm goes over rich.

And at the moment I think the idea is that the PV is shutoff after peak power to get back to the correct mixture and by retarding the ignition at the same time extend the over rev, but I am sure there is more to it.

I would love to know more about how this type of carb should be used and/or setup.


Ok now we have a stepper motor controled power jet........

The 'high compression brickwall' is no longer as hard as it used to be. With leaded fuel the compression ratio was 19,5; nowadays it is about 15. The 'brickwall' arose from the high expansion ratio (which is identical to the compression ratio). The higher this ratio, the more the burnt gases in the cylinder cool down before they enter the exhaust, thus lowering the resonance frequency of the exhaust system.
Riders complained that the engine would not rev, especially not in the lower gears, where the revs rose so quickly that the rising wall temperature of the exhaust pipes could not keep up with them. So you had cold exhaust gas and cold pipes.

The problem was to a large extent solved when the solenoid-controlled on/off-power jets were replaced with stepper motor-controlled jets that could continuously adjust mixture strenght, allowing the engine to rev more freely.

229455

This is it. The stepper motor itself originates from a Fiat Uno where it regulates the idling rpm

Regarding the Aprilia RSW/RSA125 single, Jan Thiel told me that in seven years of testing the racing department had not been able to establish which was best: low or high inertia. I would choose low.....

Frits Overmars

The tech term for what Frits is describing is Superposition of the Ex pulse.
This is easily described in a sim, where a residual pressure ratio is seen sitting at the Ex port when it is opening.
The "new " pulse is added to this residual, and a very large pressure ratio exits down the duct to the header.
The larger the initial ratio, the larger the amplitude of the wave in the diffuser - this creates a deeper depression around BDC, and it is this that initiates the biggest mass flow
from the transfers.
The lower Ex timings of 190 and below create larger residual pressure ratios,over a wider band, and thus these work with a good pipe design to use "resonance" to increase band width and also peak power.
Big problem though is this whole concept is at odds with maximising blowdown to allow good peak power and more importantly, overev power.

The sim shows RGV100 making serious power with the superposition pulse going down the duct - off the scale.

Re the trombone pipe results you did sims for TeeZee.
Look carefully when you say it seems to affect the top end "more ".
At 9000 the lowest reading is 13 Hp, the highest reading is 17 Hp, thats an increase of 4 Hp, thats 31% more power in the bottom end, that then allows the thing to rev to 17,000.
Seems a not bad result.

Re the powerjet temp result you mentioned.
The effect of the solenoid powerjet is as you described - this I only discovered recently with a datalogger that I could set the sample rate of the EGT high enough to read the temps quick enough - along
with some exposed junction probes.
I was testing a RS125 on the dyno and it was making NO power past 12500, looking at the data you could see the egt drop from 640 C to 580 in around 400 rpm.
After fixing the fact some idiot had left out the rpm plug in the loom, the solenoid now switched on at 12200, and the temp stabilised at 650 past 12500 and the thing than reved out to 13500 +.
So the powerjet switching isnt making the mixture "lean"as such, it is simply maintaining the correct mixture, and thus the temp in the pipe.




Imagine the valve passes 60 cc of fuel per minute, but the engine only needs 30 cc. How would you go about that? You could open the valve for 30 seconds and then shut it, but by that time the engine may have drowned.
Open it for one second, close it during one second, open it for one second, sounds more sensible, doesn't it? That is why I quoted the valve's frequency: 13 Hz.
That means it can open and close up to 13 times per second. This again means it could open for 1/13 of a second and close the rest of the second, or open for 12/13 of a second and close during 1/13 s, or everything in between. And of course it can stay completely open or closed; enough possibilities to govern the mixture.

The ignition timing does not have to be changed when you use an electronic power jet. But both the ignition timing and the powerjet timing are means of influencing the exhaust gas temperature. A late ignition and/or a lean mixture both cause a higher EGT, so you can match the exhaust resonance frequency to a rising engine rpm.
And if you have that power jet available, the ignition does not have to do it all by itself anymore, so you can search for a timing that gives a better overall result.

I was trying to find wobs simple answer but gave up

Oh there it is


With todays technology the bar can now be raised to around 40 crank Hp without too much drama involved, and thus achieving around 35 RWHp.
Its just a matter of careful parts selection and very careful assembly.

The alloy inserts for the TZ350 was the customers choice - once its all proven, and we get a handle on what the engine likes, then I will do some bronze ones.

AvGas in NZ is all LL100, this is low lead 100 octain.But the rating is defined differently in avaition.Its approx equiv to 100 "pump" gas, but has a lean rating of 100 and a rich rating of 130.
MNZ Appendix E defines avgas as max 112 MON amd max 108 RON.

Avgas, or any leaded "race" fuel reacts completely differently to unleaded pump gas.
In general terms the unleaded hates compression, but loves timing.Avgas is the opposite in that it makes more power up to the knock limit with more com.
Unleaded makes better power when run rich,avgas makes more the leaner you go.
Tuning in the old days with RS and TZ engines meant using lean mains and small powerjets ( 35 ) as turning off a big jet over the top would mean being too lean in the overev.
Nowdays the unleaded fuel runs rich at peak power, then uses a big powerjet ( 55) to create some heat in the pipe over the top.

[richban]

I was trying to find wobs simple answer but gave up

Oh there it is


Nice one ta. Not time to sort the power jets but will get them sorted for the street race.

[husaberg]

Nice one ta. Not time to sort the power jets but will get them sorted for the street race.

Someone could come along later and suggest that if you really want it to leap out of corners, You might want to consider putting a 50kg midget on it;)

You could also make use of vitue that it has a cassette gearbox, with freely available alternate internal ratios, then gear it for specific corners..........
Pretty sure the similar year RS250 ratios work.
I posted the available ratios a while back. they seemed to be NF5 numbers in the f3 parts list.

[Peter1962]

I have never noticed this cylinder Nor do I know what variant it is, Anyone?
306581


I think this is a DEA cylinder

[richban]

Someone could come along later and suggest that if you really want it to leap out of corners, You might want to consider putting a 50kg midget on it;)

You could also make use of vitue that it has a cassette gearbox, with freely available alternate internal ratios, then gear it for specific corners..........
Pretty sure the similar year RS250 ratios work.
I posted the available ratios a while back. they seemed to be NF5 numbers in the f3 parts list.

Yep or just splash the cash on an F3 box. Or man up and clutch it up. But when she goes from 40hp to 75 in half a second things get rather exciting.

[F5 Dave]

I've taken some pics I'll load them up tomorrow. Its all a compromise, just working out the best one I guess.

[Frits Overmars]

I have never noticed this cylinder Nor do I know what variant it is, Anyone?
306581
I think this is a DEA cylinderRight. In fact it's two DEA cylinders; the left and center pictures show a 2013 cylinder; the right pic shows a 2014 cylinder from the DEA superkart tandemtwin with RSA-based cylinders. The notches in the bore surface are supposed to retain some oil for the benefit of the exhaust bridges.

[Frits Overmars]

Wonder why RSA ran the domed piston? Frits? Ignition, triple port instead of bridge?Simple answer: the RSA made more power with a domed piston. The ignition was optimized for each test and the triple port had already been proven better than a bridged port, so all following tests were carried out with the triple port.

[husaberg]

Simple answer: the RSA made more power with a domed piston. The ignition was optimized for each test and the triple port had already been proven better than a bridged port, so all following tests were carried out with the triple port.

Could it be that say a Honda RS125 with it's less curved transfers, bridge exhaust perform better with a flat top piston on account of these factors.
Conversely say a RS Aprilia with more curved transfers performs better with a domed piston and bathtub as they are a better combination of complimentary characteristics.
Than it would be mixing and matching. (I hope that makes sense)

[Frits Overmars]

Could it be that say a Honda RS125 with it's less curved transfers, bridge exhaust perform better with a flat top piston on account of these factors. Conversely say a RS Aprilia with more curved transfers performs better with a domed piston and bathtub as they are a better combination of complimentary characteristics. Than it would be mixing and matching.Aprilia tested all combinations of Aprilia-style and Honda-style transfers, exhaust, piston shape and combustion shape. That was a lot of mixing and matching.
It could well be that a Honda RS125 with it's less curved transfers, bridge exhaust performs better with a flat top piston. But in any case it performs worse than an RSA.

[Grumph]

Right. In fact it's two DEA cylinders; the left and center pictures show a 2013 cylinder; the right pic shows a 2014 cylinder from the DEA superkart tandemtwin with RSA-based cylinders. The notches in the bore surface are supposed to retain some oil for the benefit of the exhaust bridges.

They look a bit more than just notches...Do they go through to the transfer ducts ? When i saw them in the pic I wondered if they matched holes in the piston skirt at BDC for a little under piston cooling/mixture moving through but assumed not for reasons you'd already mentioned.

[trevor amos]

Is it possible that the more compact chamber, having reduced surface area , shorter flame path, full toroid chamber profile and so on, for a similar comp ratio, are responsible for the performance step up rather than the flat top piston per se`. Or are these comments merely thoughts over reality?

Trevor

[seattle smitty]

Something that has surprised me (and pleased me, since it seems to contradict the widespread idea that our 2-strokes are doomed to disappear) is the number of little shop operations fabricating new state-of-the-art cylinders and complete engines for various sorts of kart racing, sled racing, scooter racing, and so on (including the two outboard engine builders that I already knew of). Many or most of these efforts seem to involve attempting to duplicate the last Aprilia design as nearly as possible. Also attempting this are some builders of direct replacement cylinders for Aprilias, one of whom is a fellow Netherlander of Frits and Jan Thiel, and was mentioned here by Frits, who also seems to have some level of personal acquaintance with some of the kart engine fabricators, if not the sledders.

With all of these parties (whose photos often show some beautiful work being done!) putting great effort into producing the best 2-stroke engines in their chosen sports, one might expect that one or more will eventually surpass the work of the masters. For one thing, some of them, maybe most, can work from a blank sheet of paper, whereas Thiel and Overmars have explained that they were constrained somewhat by having to build for an existing engine.

So, if, repeat IF this is something upon which you care to comment, who among the new engine-builders does our esteemed Professor Frits see as the next Luke Skywalkers, matching and/or exceeding the masters now or in future?

(There's a big caveat here, which is that the karters, sledders and boaters are currently showing only their "conventional" designs. In the matter of the FOS engine, a whole different thing, surely it will be a case of the master exceeding his own previous best work . . . ).

[wobbly]

I dont think its a case of the young pretenders exceeding the efforts of the long established masters, but more a case of taking the brilliant ideas
that have been developed in the past and learning from the results gained.
A perfect example of this would be that Jan let on that he had a huge issue at Aprilia with holing pistons once a power threshold was reached.
Jetting, ignition, compression changes had no real effect, except to reduce power.
The fix was to cut away the head insert to allow water close to the plug threads, thus better cooling the exposed plug body.
He wondered why the hell he had not thought of this 20 years earlier.
So, what do we learn here - when you have an issue with piston damage, look at the parts that can maybe ameliorate the problem, by cooling them.
KZ2 engines have always been limited in so many areas, as they have a straight line ignition.
This show up time and again as deto eating away the piston edge due to the trapped end gases in the squish being overheated by the excess timing at high rpm.
So whats the fix, cool the squish band properly.
None of the Italian factories have done anything about this, and implementing the extension of Jans idea doesnt make me a 2T genius, but does make me real grateful to the man
that passed on the knowledge.
Thats only one small example - but for sure if someone were to implement a large number of the ideas that were proven experimentally by people like Jan and even going back
to my hero Mr Fath then really big jumps in power could be had even in KZ2 where so little is allowed to be modified, I know, as its happening as we speak.

[F5 Dave]

With that lead in I'll post a pic of my engine & wish I'd cleaned the gasket goo off first as if to polish the proverbial turd.

The reed inlet I don't have a crank web handy but I've bunged a protractor in there. The skirt stub allows passage to the transfers but I'd been having ring seal issues with it largely ground away.

Honda didn't provide a case reed in 1978 so I've had to add one. This facilitates fitment in an NF4 frame so it was worthwhile just for that. The C port entry is visible from the Devcon drizzling out of it (yet to be ground back).

I'm wondering if I should trial without reed stops . . .

The skirt has no hole (Metal sprayed in the inlet port).

[speedpro]

You need a longer rod so you can raise the cylinder and un-mask the path between reeds and crankcase, or build up the inlet tract roof so it directs the flow down into the opening below the cylinder, though that's a bit limited with having to allow for the C port.

Do you have much of a problem fitting a carb to the intake? I had issues with my case reed TS100 with the carb hitting the case.

[F5 Dave]

I have to use an RGV carb nothing else will fit. Do have one bored to 35 to try again which it loved before. There is space around the sides to the transfers.

[peewee]

not sure if this amounts to anything good or bad or maybe it amounts to nothing at all but the piston travels a slightly shorter distance per crank degree with a longer rod attached. im sure frits or wobbly could better answer if this has any benefit or not. ive always thought its best to use the longest rod you can possibly fit

[husaberg]

not sure if this amounts to anything good or bad or maybe it amounts to nothing at all but the piston travels a slightly shorter distance per crank degree with a longer rod attached. im sure frits or wobbly could better answer if this has any benefit or not. ive always thought its best to use the longest rod you can possibly fit

It also dwells longer at tdc and bdc and lowers piston acceleration and allows for more crankcase volume

[ken seeber]

Peewee
The spreadsheet shows, for a 54 crank, the piston travel for a 100, 110 & 120 rods. This is based on a bore axis in line with the crank axis, ie no piston pin offset.
Longer rod offers more crankcase volume, more entry area for the transfer passages, less piston side thrust, lower peak acceleration and forces, less movement particularly towards the TDC & BDC positions. The shorter rod the opposite.
I'm sure that Wobbly & Frits could provide more subtle reasons for and against, based on the application and its limitations.
Ken

[speedpro]

The piston travels the same distance in any engine with the same stroke, irrespective of the rod length. The amount the piston travels per degree of crankshaft rotation will differ at various crank positions, sometimes more and sometimes less with different length rods. It's all down to geometry.
With longer rods the variations in velocity/acceleration are reduced which if other things are equal will allow higher revs for the same peak loads on the piston. With an infinitely long rod the piston velocity would vary at a pure sinusoidal rate and have the lowest variation in velocity.
Kawasaki ZX750 race kit rods were 2mm longer if I recall and later model FZR250(3LN) rods were 2mm longer and the pistons were 2mm shorter than the earlier 2KR models. The bore and stroke remained the same. In fact the cranks, cylinders and heads were interchangeable except that the 3LN head had bosses for the top engine mounts to the spar type frame.
Putting a 400 crank into a 350 chev creates a very torquey motor. Partly I think due to the longer stroke( and bigger engine at 388?) but also due to the short rods used which with the resultant crank/rod/piston geometry favours torque over revs and hp. Sorry, not well explained, probably 'cause I've got it wrong.

[Frits Overmars]

If this is something upon which you care to comment, who among the new engine-builders does our esteemed Professor Frits see as the next Luke Skywalkers, matching and/or exceeding the masters now or in future? I won't comment, Smitty. There are several promising people around but I can't claim to know all of them. Naming names means excluding names and that may well do unjustice to some. Who am I to know who will rise and shine in the future?
Both Jan Thiel and yours truly are trying to spread our two-stroke knowledge with the intent that you guys take over where we sign off (although I have no intention of signing off just yet).


The notches in the bore surface are supposed to retain some oil for the benefit of the exhaust bridges.
They look a bit more than just notches...Do they go through to the transfer ducts ?No Grumph, notches don't. This picture shows under what angle and how deep the cutter went in.
306604


Is it possible that the more compact chamber, having reduced surface area, shorter flame path, full toroid chamber profile and so on, for a similar comp ratio, are responsible for the performance step up rather than the flat top piston per se?Here are two combustion chambers with identical compression ratios, squish areas and squish clearances. Which one do you think has the smallest surface area?
306605 And where do you see a performance step-up?


the piston travels a slightly shorter distance per crank degree with a longer rod attached.So over 360° a shorter rod will shorten the piston stroke?


It also dwells longer at tdc and bdc and lowers piston acceleration and allows for more crankcase volumeSigh.... a longer rod dwells longer at TDC and shorter at BDC; it accelerates the piston less at TDC and more at BDC.


The piston travels the same distance in any engine with the same stroke, irrespective of the rod length. The amount the piston travels per degree of crankshaft rotation will differ at various crank positions, sometimes more and sometimes less with different length rods. Thank god someone is awake.

Yeah, I know, I sound like a grumpy old man. It's the weather, you know. Cold wind, rain... Wish I were in NZ right now.

[trevor amos]

Nice images Frits, point taken, my education continues.

But the weather here is also windy,cold and wet, but I`ve just gained a little more knowledge so that makes me happy and content, at least until the next irksome question! Thanks.

Trevor

[Grumph]

Thank you Frits - much better angle to see how deep the notches are. I suppose the question is - did they work ? If they weren't used on the later engines, the assumption is, it wasn't worth doing.

Ha, weather...two big race meetings here on successive weekends. One VERY wet, one quite warm. Not our usual early summer at all.
Big job in the workshop today - and i'm going to have to light my fire to get warm enough. Enough to make me a grumpy old man...

[F5 Dave]

Gee Greg I would have never thought of you as grumpy. More jolly. Actually what with that white beard. . . hey wait a minute.

Are there any elves in this workshop of yours?:scratch:

My son says he`d like some hot wheels cars and my daughter blithered something about a pony, but I`m not sure we could fit one in the oven.

[wobbly]

The fact that a long rod dwells at bdc LESS was the only reason I could think of that Honda persisted with the short rod 105/54 approach for so many years.
Less dwell = less effective transfer STA and maybe they figured this effect overcame any perceived advantage gained from a long rods less angularity thus
bore friction, plus better combustion from dwelling more at TDC.
The other factor to consider with a reed valved engine is that they dont respond favourably to big case volumes like a RV does, with around 1.3 being
the effective bottom limit on case size.
Mentioning the 400 Chev, this had a huge issue with bore friction due to the insanely short rods,but the short rods also give an advantage in
engines that have not very efficient intake ports .
This being due to the faster acceleration away from TDC getting the intake charge moving faster/earlier as the peak piston acceleration is earlier as well..
As usual though in the many tests done by magazines they didnt optimise the cams to take advantage of the differing rods characteristics.
Always more to it than meets the eye.

[Grumph]

Gee Greg I would have never thought of you as grumpy. More jolly. Actually what with that white beard. . . hey wait a minute.

Are there any elves in this workshop of yours?:scratch:

My son says he`d like some hot wheels cars and my daughter blithered something about a pony, but I`m not sure we could fit one in the oven.

Oh, very good try - but guys who use as much devcon as you, are on the naughty list...
Kev left a pass for me at Levels gate, saying Santa in a silver van would pick it up...One of the girls on the gate squealed and screamed, "it's him !" The other looked closer and asked for ID...Kev has paid for that one.

[Frits Overmars]

Thank you Frits - much better angle to see how deep the notches are. I suppose the question is - did they work ? If they weren't used on the later engines, the assumption is, it wasn't worth doing.That picture was from a 2013 DEA cylinder because it showed the notches best. But the 2014 cylinder has them too, so they can't be all bad.
Andrea degli Esposti (DEA) is a free thinker who does more than just copy Aprilia stuff. Here he is with his home-built pulsating flow bench.

[F5 Dave]

Anyhoo, back to whether a case reed like mine shrouds the C port entry. . .

[senso]

That an interesting machine, if not asking much, could you(Frits) explain a bit what it does and how it does its work?
There is a stepper attached to the crank probably to rotate the engine, the hose in the intake might be a positive air pressure, and then there is a sort of x-y table on where the head would go, is it used to scan the bore in steps while measuring pressure(like a pitot comb, but instead of a use array of sensors/pitot tubes it scans the entire bore), or I'm totally wrong about my assumptions?

Regarding the con-rod angles, I have a simple excell file to calculate/graph the con-rod angle and the piston position, its very basic, you can only enter the stroke and two con-rod lengths and thats it, its clean of virus and trojans(at least I think my laptop is clean).

[wobbly]

Dont understand the need for the question about the C port duct entry, you can clearly see the reed stops are miles away
and there is nothing impeding the flow into the bottom of the cylinder in that area.
If you wanted you could put a radius on the bottom of the case, below the gasket surface that helps flow turn the corner.

DEAs anemometric flow tester uses a single tube with 10 i think individual pitots inside.
This detects flow vector as well as velocity passing the tubes end.
The pitot is CNC controlled to develop an array of measurements all around the cylinder and this is then displayed on a screen with coloured areas of differing velocity
showing how the scavenging streams interact.

His pulsating bench simply allows controlled " puffs " of flow to be sent thru the transfers/Ex - this was first developed at Queens by Flec etal and much closer simulates
what actually occurs in a running engine - ie its not constant flow like you get from a Superflow etc developed for 4T use.

[peewee]

The piston travels the same distance in any engine with the same stroke, irrespective of the rod length. The amount the piston travels per degree of crankshaft rotation will differ at various crank positions, sometimes more and sometimes less with different length rods. It's all down to geometry.
.


nobody said the total amount of stroke would change with different rod lengths. we all know the full stroke remains the same regarless of 100mm rod or 10000mm rod. i merely said the amount of piston travel per degree of crank revolution will vary with different lod lengths. i 'briefly' looked at a calculator last night, between 0-180* it appeared the piston always traveled a lesser distance per degree with the long rod, except near tdc/bdc where both rods appeared to be the same. maybe i need to look again at the calculator ?

[senso]

The xls that I attached does just that, calculates all the values for a full rotation( 360º), and plots them in two separated graphs, made it just to prove someone that different rod lengths do indeed change the rate that the piston moves with each crank degree.

[peewee]

never mind guys. i think i was misinterpreting the calculator wrong. around 90* is that where the longer rod travels further per degree than a short rod ?

[F5 Dave]

Dont understand the need for the question about the C port duct entry, you can clearly see the reed stops are miles away
and there is nothing impeding the flow into the bottom of the cylinder in that area.
If you wanted you could put a radius on the bottom of the case, below the gasket surface that helps flow turn the corner. . .

.
thanks
it was more if the skirt would shroud any reverse flow back up the C but if reed will feed it fully then I'm ok.

[wobbly]

Peewee, read the bloody posts in here.
A long rod dwells LONGER around TDC and SHORTER around BDC, the opposite for a shorter rod.
That is why I wondered about Honda using short rods - they dwell at BDC longer thus effectively increasing the STA of the transfers.

[peewee]

Peewee, read the bloody posts in here.
A long rod dwells LONGER around TDC and SHORTER around BDC, the opposite for a shorter rod.
That is why I wondered about Honda using short rods - they dwell at BDC longer thus effectively increasing the STA of the transfers.


youll have to forgive me. fixing train railroad tracks is my normal job. working on engines is just a hobby. alot of things ive yet to learn :laugh:

[monkeyfumi]

So a long rod would give minutely more STA for blowdown?

Edit, no, hang on, I think I have that wrong...

[2T Institute]

Yeah, I know, I sound like a grumpy old man. It's the weather, you know. Cold wind, rain... Wish I were in NZ right now.

Have some 45 deg days and 35deg nights to swap:lol:

[senso]

I might have my numbers totally wrong, but lets just compare a 105mm rod and a 115mm one in a 54.5mm stroke engine, the maximum rod attack angle for the 105mm one is 31.2º and for the 115mm one its 28.2º.
Regarding rod angle here is an image(blue line is the 105mm rod, 115mm is the red one, the same for the second image):
306623

306624

For me seeing the values is more intuitive than looking at number, I think that calculating the derivative of the rod angle would also be nice to see, so the acceleration values can be "seen".

[peewee]

hondas way of thinking seems like old hat. i would rather learn from jan and frits :D

[wobbly]

Yea well Hondas thinking may be old hat but making those sort of statements leaves you open to plenty of informed derision.
Consider the final year of the 250GP championship.
Who won, Honda and Aoyama, a rider that by all standards since, has made it obvious he could not ride his way out of a brown paper bag - even his injuries not withstanding.
Sure - plenty of excuses from Aprilia about Jan retiring and the resident idiots at the factory "improving " backwards what he had done previously, plus the problem
of the RSA having a front pipe that upset the weight bias on the front wheel, but still, the factory supported Honda didnt lack top speed, acceleration. nor handling.
The Aprilia riders also stole points off each other, making things doubly difficult, but Honda did the job with a 105 rod on a 54.5 stroke, Showa forks, useless reed valves, a No Name team and and only 1 dickhead for a rider.
Explain that in succinct technical terms - not wild generalities.

[husaberg]

Yea well Hondas thinking may be old hat but making those sort of statements leaves you open to plenty of informed derision.
Consider the final year of the 250GP championship.
Who won, Honda and Aoyama, a rider that by all standards since, has made it obvious he could not ride his way out of a brown paper bag - even his injuries not withstanding.
Sure - plenty of excuses from Aprilia about Jan retiring and the resident idiots at the factory "improving " backwards what he had done previously, plus the problem
of the RSA having a front pipe that upset the weight bias on the front wheel, but still, the factory supported Honda didnt lack top speed, acceleration. nor handling.
The Aprilia riders also stole points off each other, making things doubly difficult, but Honda did the job with a 105 rod on a 54.5 stroke, Showa forks, useless reed valves, a No Name team and and only 1 dickhead for a rider.
Explain that in succinct technical terms - not wild generalities.

Hondas strength are also its weaknesses... Honda have huge resources but they have huge committees.
Honda can't be seen to be copying off others so they tend to carry on with what they have already.
Sometimes there corporate pride cost them, they have to use Showa forks even if Olhlin's would make them lap a second faster.
They have to use Keihin carbs.
They pretty much had to keep with the RC valve
On the NSR250 they had to keep with the ELF patented Proarm.......
Most other companies were not hamstrung by these things.
Later on they had to keep to a certain fuel consumption, prior to the fuel limits

[peewee]

the worst part is we probly would have something even better than rsa125 if jan had no boundaries to work from. starting from scratch i bet he could make one hell of a engine

[Frits Overmars]

That an interesting machine, if not asking much, could you(Frits) explain a bit what it does and how it does its work? There is a stepper attached to the crank probably to rotate the engine, the hose in the intake might be a positive air pressure, and then there is a sort of x-y table on where the head would go, is it used to scan the bore in steps while measuring pressure(like a pitot comb, but instead of a use array of sensors/pitot tubes it scans the entire bore), or I'm totally wrong about my assumptions?You're totally right, Senso.


DEAs anemometric flow tester uses a single tube with 10 i think individual pitots inside. This detects flow vector as well as velocity passing the tubes end. The pitot is CNC controlled to develop an array of measurements all around the cylinder and this is then displayed on a screen with coloured areas of differing velocity showing how the scavenging streams interact.Like so:
306637


Consider the final year of the 250GP championship. Who won, Honda and Aoyama. Sure - plenty of excuses from Aprilia about Jan retiring and the resident idiots at the factory "improving " backwards what he had done previously, plus the problem of the RSA having a front pipe that upset the weight bias on the front wheel.Would you care to indicate that front pipe Wob :devil2:? It was the RSA125 that suffered from an upset weight bias because of the front pipe, not the RSA250.

(make sure you watch these pictures in maximum magnification :eek5:)

[Grumph]

The other factor to consider with a reed valved engine is that they dont respond favourably to big case volumes like a RV does, with around 1.3 being
the effective bottom limit on case size.


That statement crept in without much comment Wob...as Prof J S Miller used to say, "why is it so ?"

Does a too large volume act effectively as an air spring, delaying reaction from the reeds ? Not so with the mechanically driven valve I'd imagine.
You'd think that given equally good transfers and pipe, the reed motor would like equally large case volume, but apparently not so....

[Frits Overmars]

as Prof J S Miller used to say, "why is it so ?"Or, as I like to say: "Is it so?"
My experience with reed valve engines is limited, but I've been led to believe that the crankcase volume of a Honda RS125R is about the same as that of the Aprilia RSA. Have you got any values handy Wob?


You'd think that given equally good transfers and pipe, the reed motor would like equally large case volume, but apparently not so....I too would imagine that a reed engine would like an equally large case volume, so any pressure drop in the transfer ducts during scavenging is kept within limits without the need to instantly accelerate the contents of the inlet tract.

A difference that does come to mind: rotary valve engines like large carburettors; reed valve engines seem to care less. Apparently they compensate for smaller inlet duct cross-sectional areas by keeping the reeds open longer, something a basic rotary valve can't do.

[husaberg]

That statement crept in without much comment Wob...as Prof J S Miller used to say, "why is it so ?"

Does a too large volume act effectively as an air spring, delaying reaction from the reeds ? Not so with the mechanically driven valve I'd imagine.
You'd think that given equally good transfers and pipe, the reed motor would like equally large case volume, but apparently not so....

Both Frits has seemingly alluded to it maybe is the case,and Wob has mentioned it before the Wob one was in regards to a Honda RS250 speed record attempt Honda I think.
I will find the quotes later.


Again this is the old story of trying to put specifics onto a huge generality.
The reed cavity of course is connected to the case, and it depends entirely what the total volume is,as to the advisability of
filling in the so called dead areas.

I have found that unlike a full noise rotary valve engine there seems to be no power increase if the case volume is made bigger than a 1.3 ratio when using reeds
be they direct into the case or cylinder mounted.
And another generality seems to be that the crappyer the transfer ducts, the ratio should tend the other way toward a smaller 1.4 ratio.

If the case was too small to start with and you fill the reed cavity dead areas, this will make it worse, and vise versa, but as all the factories are now tending toward making the reed box
smaller and smaller it would seem that filling the cavities and also filling the volume in front of the reed ( to the point where you would think the flow would for sure be affected badly )
then I would say its a good thing AS LONG AS YOU ARE MEASURING AND CORRECTING THE TOTAL CASE VOLUME.


In my testing I have found no more power going to a bigger than 1.3 case on a reed engine.
This is a function I believe of the efficiency of the rotary valve intake system being able to better fill the case at high rpm,using the 1.24 as Frits has described , but having said that
I have only just crept over 50 Hp with a 125 reed, and the Aprilia RV made alot more than that, so maybe a huge case simply isnt needed at the lower bmep.

[wobbly]

Yea as you would say Frits "glad someone is awake " - the comment about the RSA front pipe upsetting the balance had nothing to do with the 250 issues - was just an example of
one of the many "excuses" from Aprilia land about a reduction in on track performance.
The Jan inspired new engine was obviously better, the 125 chassis wasnt ,but sadly the two arent mutually exclusive.

I have got into many heated discussions about Aoyama and the Honda winning the title that year but it always comes back to the same issues for me.
How the hell did it happen if the Showas are a second a lap slower.
Then worse - reed valves,short rods and flat tops are useless.
The rider has since proven to be of limited skill, pretty much a death blow.
And worst of all it was a very old design including the silly skinny pipes,as Honda had stopped serious development of the 250 several years previously.
The Scott 250GP team had one Honda technician, the rest were for sure not famous in pit lane but they collectively kicked Aprilias arse.
And yes the Aprilia boys did some dumb shit, and were continually stealing points off each other, etc etc, but the Honda was fast enough to win with all those
issues that many would have me believe should make being even top 10 impossible.

A Honda RS125 has a case com of exactly 1.32 with a VF2, measured it several times, the reeds glued shut and the case filled up to the top of the transfers.
Then the piston run to the top of the bore,and finally filled to the top thru a hole in the dome.
Thus ensuring the transfer ducts are completely full.
A stock reed will have a little more case vol but looses power everywhere.
Then I machined 5mm off the reed box face - lost overv power past 13,000 but gained alot of mid.
Then added a 10mm spacer, so + 5 over stock - lost power everywhere.

Here is another example, a YZ85 for Flat Track racing.
The big case has some more power well into overev, but its never used.
I have done dozens of sims on all manner of reed engines and have never seen one make better power under 1.3 case com.

Latest test - TM KZ10B, add a 5mm spacer to the reed box,loose 1.5 to 2 Hp up to peak, gain 0.5 at 14500,so my next test will be to
machine that case to take 5mm off the reed box when I rebuild the dyno engine.
Gaining mid is real hard in those engines, getting overev power is easy with timing and a shorter pipe/manifold and a smaller stinger insert.

[Grumph]

Or, as I like to say: "Is it so?"
My experience with reed valve engines is limited, but I've been led to believe that the crankcase volume of a Honda RS125R is about the same as that of the Aprilia RSA. Have you got any values handy Wob?

I too would imagine that a reed engine would like an equally large case volume, so any pressure drop in the transfer ducts during scavenging is kept within limits without the need to instantly accelerate the contents of the inlet tract.

A difference that does come to mind: rotary valve engines like large carburettors; reed valve engines seem to care less. Apparently they compensate for smaller inlet duct cross-sectional areas by keeping the reeds open longer, something a basic rotary valve can't do.

Ah, but do they keep the reeds open longer ? i remember Jennings writing up reeds in Cycle mag and quoting an SAE paper by the Yamaha guys who developed the DT/RD series. They found that yes, the opening period varied - as did the timing - but at peak RPM the reed timing was the same as the roadrace rotary valve timing they were familiar with. That was with the very basic steel reeds of the period, i have no idea if the modern composite reeds act differently.

[jonny quest]

While that info is great Wobbly, you're changing more than just case volume when you're changing reed box length. Is it inlet tract length that's doing more of the gains/loss? I'd hazard a guess and say so over cases volume

[wobbly]

Wrong - making the case shorter, or adding a spacer has NO effect on the intake tract length, that is defined as reed tip to bell end.
Here is the KZ10B intake - made as short as possible by recessing the manifold into the reed block.
The spacer is 5mm and will be added to the case after machining to be able to make the case volume back to stock, no effect whatever on the tuned length..

One reason I believe that a VF reed block makes more power, apart from the increased tip curtain area, is that the W configuration
will always reduce the case volume a little - and many engines have the case too big to start with due to the specific layout - like the YZ85.

When the case is bigger you have to make the reeds thinner to get them to open as much as previously.
With the case down at 1.24 the reeds need to be so soft they very quickly begin to go spastic from what may loosely be called " flutter ".
ie overbending and or smashing into the stops at higher rpms, due in part to their own natural vibration frequency coinciding with the harmonic frequency of the intakes tuned length..
When this happens, power drops dramatically as you can imagine.

[peewee]

wobbly since we're on the subject, whats the formula for case comp ratio ? i figured about 680cc volume in the banshee with the piston at tdc, pouring oil through a hole in the dome. thats with oem rod, oem reed block, 64mm piston, 54mm stroke. basically a bone stock engine. when i enter 680cc into engmod it says 1.43:1. not quit sure how it arrives at 1.43

[Frits Overmars]

crankcase compression ratio = TDC-volume / BDC-volume

TDC-volume = 680 cc (I'll take your word for it)

BDC-volume = TDC-volume - cylinder volume

cylinder volume = 173,7 cc

BDC-volume = 680 - 173,7 = 506,3 cc

crankcase compression ratio = 680 / 506,3 = 1,343

And now for some reverse engineering:
what TDC-volume will give a crankcase compression ratio of 1,43?

TDC-volume = comp.ratio / (comp.ratio - 1) * cylinder volume

TDC-volume = 1,43 / 0,43 * 173,7 = 577,7 cc.

[peewee]

thnx frits i think i figured it out from one of your earlier posts. 680/ (680 - 175)= 1.346

i have made the bridge between the main exh and aux, 3mm wide. does that sound about right to you guys for a 64mm bore or could it be a bit narrower and still work fine ? unfortunatly these are iron lined cylinders.

one other question. seems a bit strange but engmod says my STA will be good at 10.5k rpm and 80hp on these yamaha cylinders. 188* main 70% bore, aux fairly large width and opening 3* after the main window. A trans 126* and stock width, B 128* and widened as much as i could. C 128* stock width. i know the blowdown is based on crank degrees and area but does 30* blowdown seem in the ballpark ?

[wobbly]

Post the STA summary page for the Banshee on here, then we can say for sure what is right and what isnt.
30* of blowdown is a meaningless number, everything depends upon the interaction of all the Specific Time Areas.
Quoting one tiny part of the overall relationships in any engine is an exercise in futility.

[peewee]

not sure if you can read it. is there a way to make the photo bigger ? i guess if you double click then it gets bigger. learn something new everyday

before you ask why the reed block is much higher its because its using the vf4 which shows alot of improvement over the stocker

wobbly about the 3mm wide divider between the main and aux. does that sound right or can i narrow it a bit without mechanical problems ?

[wobbly]

3mm is fine with a nicasil cylinder, seen plenty of bridges that narrow with no issues at all.
But the narrow width will wear quickly in an iron bore.
Making the bridge thinner isnt the way to go, getting the Aux shape and especially grinding a pocket into the rear wall to get radial
flow exiting down the duct is way more productive.
The STA numbers are fine.
The VF reeds nearly always have alot more tip curtain area than the area of the ports in the block, simply as the V angles are narrow.
But this will not be an issue for power production at all with the numbers shown.

[husaberg]

I have never noticed this cylinder Nor do I know what variant it is, Anyone?
306581


Right. In fact it's two DEA cylinders; the left and center pictures show a 2013 cylinder; the right pic shows a 2014 cylinder from the DEA superkart tandemtwin with RSA-based cylinders. The notches in the bore surface are supposed to retain some oil for the benefit of the exhaust bridges.


They look a bit more than just notches...Do they go through to the transfer ducts ? When i saw them in the pic I wondered if they matched holes in the piston skirt at BDC for a little under piston cooling/mixture moving through but assumed not for reasons you'd already mentioned.


I won't comment, Smitty. There are several promising people around but I can't claim to know all of them. Naming names means excluding names and that may well do unjustice to some. Who am I to know who will rise and shine in the future?
Both Jan Thiel and yours truly are trying to spread our two-stroke knowledge with the intent that you guys take over where we sign off (although I have no intention of signing off just yet).

No Grumph, notches don't. This picture shows under what angle and how deep the cutter went in.
306604

Here are two combustion chambers with identical compression ratios, squish areas and squish clearances. Which one do you think has the smallest surface area?
306605 And where do you see a performance step-up?

So over 360° a shorter rod will shorten the piston stroke?

Sigh.... a longer rod dwells longer at TDC and shorter at BDC; it accelerates the piston less at TDC and more at BDC.

Thank god someone is awake.

Yeah, I know, I sound like a grumpy old man. It's the weather, you know. Cold wind, rain... Wish I were in NZ right now.


Thank you Frits - much better angle to see how deep the notches are. I suppose the question is - did they work ? If they weren't used on the later engines, the assumption is, it wasn't worth doing.

Ha, weather...two big race meetings here on successive weekends. One VERY wet, one quite warm. Not our usual early summer at all.
Big job in the workshop today - and i'm going to have to light my fire to get warm enough. Enough to make me a grumpy old man...


That picture was from a 2013 DEA cylinder because it showed the notches best. But the 2014 cylinder has them too, so they can't be all bad.
Andrea degli Esposti (DEA) is a free thinker who does more than just copy Aprilia stuff. Here he is with his home-built pulsating flow bench.

So these notches are just like the round divots some piston to retain prevent seizures?
306663

Ah, but do they keep the reeds open longer ? i remember Jennings writing up reeds in Cycle mag and quoting an SAE paper by the Yamaha guys who developed the DT/RD series. They found that yes, the opening period varied - as did the timing - but at peak RPM the reed timing was the same as the roadrace rotary valve timing they were familiar with. That was with the very basic steel reeds of the period, i have no idea if the modern composite reeds act differently.

https://books.google.co.nz/books?id=A9KsF2rtSmQC&pg=PA35&lpg=PA35&dq=when+yamaha+developed+their+125+motocross+engin es&source=bl&ots=i9bdqDA_pa&sig=PcwHnJlCbzrbgzX5K7-B4_D2CI4&hl=en&sa=X&ei=2ieNVKmVCqbVmgW6moCwDQ&ved=0CDwQ6AEwBQ#v=onepage&q=when%20yamaha%20developed%20their%20125%20motocr oss%20engines&f=false

pg 40 of the Robinson book it has the papers that Yam published referred to.
306661

[wobbly]

Just a couple of minor points to add.
In the pic of the KZ10B intake the tuned length isnt quite as i drew the line from reed tip to bell end.
The length as should be used for sim accuracy is a point 2/3 of the distance down the block toward the tips ( the effective length of the reed port
opening varies as the petals are closed or fully open ) and the carb bell needs end correction for the actual reflection point off atmosphere.
In a PhD thesis paper i supervised we instrumented a YZ125 fully on a dyno at Uni for using fibre optics in the combustion chamber to control
fuel injection via the colour spectrum of the flame.
One thing discovered was the actual effective length of the intake, and it varied with reed tip opening, plus it showed that the end correction was
accurate when set at approx the intake curtain area length past the full bell diameter.
Without a bell, the end correction reflection point was the classically accepted 1/2 D of the intake pipe.

Re reeds staying open longer when the intake or the block ports are restricted in area.
Yes this is true, to some extent.
When I was testing a 485 Banshee based cylinder,the reed box was designed to have a CR250 sized block.
In the sim this showed that the 8 petals were only opening approx 4mm to make the required 60 crank Hp per cylinder.
Swapping the reed for a CR125 block that is 8mm narrower the power was identical, but the reeds were opening around 8mm ( actually impossible on the inners
of a VF3 )
The opening point of the reeds was pretty much identical,dictated by the case going negative plus the intake going positive from harmonic length tuning.
The big reeds closed a little earlier, but the intake flow was more dictated by the lift/tip area profile - with the small reeds petals jumping up to the stops
real quick, staying there then dropping real fast.
In reality the smaller reed made less power initially on the dyno, but I discovered that when the blocks were centred on the bore ( the large reed was offset outward to get it to fit )
the smaller reed made more power due to having symmetric flow into the case.

This leads onto understanding why having differing reed stiffness on the top and bottom of reed intakes works well where the manifold is on a vertical angle to get the fuel height correct in the carb bowl.
There is then also more power to be had when the petal stiffness is varied horizontally across a reed block, where the intake is bent to the side, as in a modern MX engine.

[peewee]

frits and wob. ill start cutting the aux ports in the next few days. might even get started today marking out the lines and what not. irrespective of how far around back of the cylinder i can take the window, should the rear wall be aiming nearly at the bore center like the drawing or is there more current knowledge that i should be following ?

[wobbly]

Thats exactly what i was saying about radial wall exit angle and a pocket to turn the flow.
Most ,even very current designs, have a very shallow rear wall exit angle that is real bad for blowdown flow efficiency.

[peewee]

ya i know what you meant about grinding in a pocket at the rear. still you didnt really say where the rear wall should be aimed. at the bore center or farther back toward the intake ?


what you think about this on the exh bridge if i keep it at 3mm ? ill be using different pistons with no cutout in front of the wristpin but you get the idea.

[F5 Dave]

So given a smallish tunnel after creating a pocket, I ovalised the tunnel to maximise area, the flow presumably will still be restricted by the tunnel but the pocket is still worthwhile? I've kinda done it anyway.

[peewee]

question for you guys using yamaha cylinders. is 11k rpm (4186 fpm meen piston speed) acceptable or do you try to keep it lower ? ill be using high qaulity long rods above 2:1 ratio with good bearings

[wobbly]

If you read my post I said that the radial exit angle and pocket in the Aprilia drawing are exactly what I was referring to, shallow rear wall angles dont work as well at all.
With good cranks and piston parts 11K is safe as houses.
I have many engines out there with 58 cranks and 115 rods that have been running for 2 seasons of road racing with the rev limit set at 12,000,no issues at all.
The piston oil holes are fine as long as they are sealed by the bridge as they run over it.

[2T Institute]

The HRC A kit 250 cranks have 109mm rods

[senso]

Goodnight everybody, sorry for the off-topic, but its a quick question.
Does anyone here knows if I can safely open boost ports in an aprilia rs 125 cylinder that does not come with them from the factory?

[peewee]

hell maybe ill try for 12k then :woohoo:

[seattle smitty]

Okay, every website has to have someone who asks the really dumb questions; y'all should thank me for providing this service here so that none of you has to . . .:weird:

My dim understanding is that the most efficient, lowest drag, highest flow passage (gas or liquid) would be a straight port with a circular cross-section. Since air is HEAVY, and fuel even HEAVIER, and tend to pile up on the outside of a turn, the most effective (low-drag, etc.) cross section for the port where it makes a turn is some variety of oval (depending on how much of a turn, velocities, the particular fluid). I'm ignoring surface-finish here, important as that probably is.

Getting more specific, our engines require that as the ports get closer and closer to where they meet the cylinder wall, they have to assume some variety of fairly square or rectangular shape, with radiused corners. So, whatever might be the ideal, low-drag port shape, it will have to make a transition to the required shape needed at the point of entry into the cylinder.

But back where the air/fuel enters the transfers, and over the (relatively) long sweeping turn the modern transfer passage makes on its way toward the cylinder entry, the website dummy might guess that those transfers should be round-to-oval in cross-section . . . and NOT what we actually SEE in all the high-powered cylinders photographed on these pages. THEIR transfers are squares or parallelograms or trapezoids or anyway some shape with mostly straight sides, and very often with rather minimal radiusing of their corners. Certainly there can be "packaging" considerations, especially where working with an existing engine with inconveniently located studs and other impediments. But I see these straight-sided angularly-shaped ports being used in new, clean-sheet-of-paper engines, including singles (which presumably have lots of available space).

Thus, the question: Am I wrong in feeling that the "best" transfers would start with symmetrical oval shapes that only gradually transition to the shapes and angles of the port-entry? They don't have to be huge; indeed the better-flowing the shape, the less cross-sectional area it should need.

The sharp corners of the parallelogram-shaped transfers I see just look real draggy . . . and wouldn't that be an effect that increases with the square of velocity?

(Round/oval ports surely would call for some re-thinking of the crankcase where it feeds the transfers . . . although I think Wobbly has suggested that most of the A/F that gets transferred into the cylinder when the port windows open was already in the transfers).

[wobbly]

As long as the porting STA numbers are correct for the rpm and you have EVERY other aspect of the design spec'd to suit that rpm then
the higher the rpm the higher the power - as long as the torque holds up for long enough.
In the case of the Banshee style engine I have done designs with peak power at 11,000 and usable overev to 12,000.
With close to 100 RWHp on a Dynojet this is reliable and doable.

Re the port/duct shape.
The one thing you have not considered in the idea of an oval entry transitioning to rectangular is that the raw "flow" number ( cfm ) is only a part of the scenario.
The most important aspect is what I call " stream coherence ", that is keeping the transfer flow going in the correct direction,and keeping its shape as a coherent column.
These coherent columns ( that for example dont bend around the corner and exit thru the exhaust ducts, the main or Aux ) then coalesce together and form
Frits leaning tower concept.
Again this works best when it also is coherent in its shape and direction vector,ie leaning back.
Forming the coherent streams can only be done by having as much of the A/F mixture in the duct being directed to form a column of a particular shape as early as possible.
The side wall angles form the side wall shape of the column and the roof shape of the duct forms the top of the column and especially directs its axial exit angle.
Due to its inertia effect the flow has no option but to closely follow the outer wall, but the inner walls shape is super important when trying to maximise the discharge coefficient
thru the port into the cylinder.
Thus as we know from long experience, keeping the duct side walls consistent in angular direction with no axial twist or two dimensional directional changes, gives the best combination
of angular stream control into the cylinder,and flow coherence creating the scavenging regime as desired.

[2T Institute]

Goodnight everybody, sorry for the off-topic, but its a quick question.
Does anyone here knows if I can safely open boost ports in an aprilia rs 125 cylinder that does not come with them from the factory?

SUb exhaust in a RS 125 road bike (Rotax 122/123) ???

[F5 Dave]

I haven't seen one but usually the water jacket precludes that sort of carry on. I barely managed it in an aircooled barrel that had a jacket added.

[peewee]

if theres no stud in the way you should be able to cut the waterjacket open and weld that area. you may have to weld on a balloon shaped jacket on the exterior so you still have water flow around the new aux tunell. this all just guessing as ive never seen that particular cylinder

[seattle smitty]

Re the port/duct shape.
Forming the coherent streams can only be done by having as much of the A/F mixture in the duct being directed to form a column of a particular shape as early as possible.


If "as early as possible" is essential, then my notion was no good. Is that something that actually has been proved, or is it just the way everybody does it right now, and maybe in ten years they'll have something different?

I wonder if a part of the potential of Frits' new engine could come from getting away from those parallelogram-shaped ducts, and from ducts whose roof and floor are not formed around the cylinder concentrically but are shaped for low-drag (insofar as possible). I just don't see what's desirable about those concentric floors in particular, especially not without big radiuses in the corners. Wobbly, I really do get that this aspect of trying to make low-drag ports is not independent of a lot of other considerations, but it's the aspect I'm curious about at the moment.

If I had more brains, I could devise a software program that would draw a port, starting from where it enters the cylinder and working back upstream while making the turn and transitioning to the least draggy, smallest area (consistent with airflow-at-velocity requirements) port shapes as it proceeds toward the cylinder base (and on into the case). And if you asked it, it would give you right-angle slices of this optimal port at any point so you could see how the transition occurs. It would have to account for the weight and inertia of the gas, the fact that the flow is faster somewhere in the center of the air column and slower near the port walls, the effects of getting the gas column to make a turn (somewhat compressed on the outside of the turn), and give you a floor shape that the air could follow without stalling (golf-ball fans, take note). But, alas, I couldn't even RUN or understand such a program, which probably exists somewhere . . . .


Among today's conventional designs, somebody here had a photo of a big-bore motor I hadn't heard of (500cc twin, maybe?), and it had ports that went part of the way toward what I'm asking about. Naturally, I can't find it now, but possibly I can describe it. In particular, the inside wall (i.e. closest to the cylinder, or what car guys call the short turn) of the B transfer was square to the other three walls of the port itself, and NOT conformed to the cylinder.

[wobbly]

The inner side of the transfer duct produces the WORST result when it has ANY relationship to the bore.
The classic teacup handle shape is even more important on the short side than it is on the outer wall.
As I said the flow has no choice but to adhere to the outer wall shape - crap or superb as it may be for the flow relationship ( ie cfm )
The real trick is to create a short turn shape that promotes the best discharge coefficient thru the duct turn into the bore.
One thing Jan and Frits seem to be convinced of is the short turn and its synergy with the piston shape ( a dome ) to get flow adherence to the piston crown to
promote cooling of the pistons surface.
I havnt personally seen any evidence of the effect, with as I have described previously the flat top pistons of a Pavesi KZ2 that showed no evidence
of excess piston heating over and above a " normal " Maxter or TM setup with a 7* conic dome.
Now we have reports of flat tops making more power in supposed stock KZ2 cylinders.
Till I do the testing myself ( soon ) I believe the jury is still out.
My real problem is that the only way I have been able to get a flat top to make as good as or better power over a dome in a Honda was to use a severe toroid head shape.
This seems to be a real issue to achieve within the KZ2 rules, but I have no problem with a toroids extra surface area within the combustion space as I personally believe the heads inner surface
" should " be hotter than the transfers for example,as reducing the temp delta in this area reduces the temp ( thus pressure rise ) loss to the water.
I have for years thought that we should have two water flow regimes, one to cool the outer transfer walls ( to increase the volumetric efficiency ) and another hotter circuit to cool the head
( to reduce the heat loss of combustion due to the temp delta differential ).
KZ2 then has the added propensity to deto within the squish area, so i believe the ultimate scenario with this oddball system is to ceramic coat the chamber, but cool the squish band as effectively as possible.

[peewee]

this is just my thoughts. i know the definition of parallelogram and i dont think the rsa fits that description at all, infact the rsa B transfer opening at the cylinder base appears to have all 4 walls nearly sqaure with each other, for the most part anyways. now if you look at a modern ktm 250 or 300, those cylinders appear to be the perfect definition of parallelogram. '02+ cr250 cylinder has a shape closely resembling a paralellogram as well.

regarding the inner wall of B being sqaure with the other 3 walls, versus following the bore curvature, on the rsa you can clearly see the inner wall doesnt follow the bore curvature but rather is fairly sqaure with the other 3 walls. i cant explain the purpose but im sure frits could. i havent seen this 4 sqaure walls thing on any mass produced mx type of cylinder from honda, yamaha, ktm etc, atleast not on the larger cc engines, but i think all the race type cylinders have the walls sqaure with one another, atleast the few i have seen anyways, but then again many of them are just copies of the rsa, so of course they will have nearly identical features of the rsa



it may be hard to tell from the photo but if you were looking straight down on this cylinder, the transfer opening at the cylinder base is almsot a exact paralellogram. the full race cylinders ive seen, such as rsa, are not even close to this shape. the inner wall of B on this particular cylinder follows the round curvature of the bore as you can see in the pic

included is another pic which makes it clear. the corners of the B entrance appear almost 45* to each other. the A corners are about 90*. i forgot what im even rambling on about. time to go to bed i guess

[teriks]

...
My dim understanding is that the most efficient, lowest drag, highest flow passage (gas or liquid) would be a straight port with a circular cross-section.
...
Yes, the circular cross section maximizes flow for a given cross sectional area. When you add the question of available space for ducts, and Wob's reasoning above, the table for sure turns towards "squareish".

[senso]

SUb exhaust in a RS 125 road bike (Rotax 122/123) ???

Yes, exhaust auxiliar port(might be wrong to call the exhaust boost ports, sorry the confusion).
There is at least 3 different aprilia rs(in fact rotax engines, 122 and 123 if I'm not mistaken), there is the earlier one with just the oval exhaust port:
306697

Then there is the next version, with exhaust aux ports:
306698

And the last one, with exhaust aux ports, and a small port that goes from the intake directly to the crankcase:
306696

Sorry for the tiny pictures, that was the best I found in a 2 minute search, but they grow a bit if you click on them.

I have already made some aux exhaust ports in a couple of cylinders, but as I don't have any aprilia/rotax cylinder to see/measure to be sure, and because its sort of a common engine, I tried asking you guys if someone might know if its possible to do without welding anything.

[Frits Overmars]

Does anyone here knows if I can safely open boost ports in an aprilia rs 125 cylinder that does not come with them from the factory?
if theres no stud in the way you should be able to cut the waterjacket open and weld that area. you may have to weld on a balloon shaped jacket on the exterior so you still have water flow around the new aux tunell.You could do all that. You could also buy the same cylinder with aux exhausts; that would be a lot simpler and probably cheaper too.
EDIT: I see that Senso has discovered the various cylinder models as well.
A thing to watch on these Rotax cylinders: the water passages upward from below the exhaust duct are tiny at best; often they are partly or even completely blocked by casting-skin. The pic shows what I mean.

[Frits Overmars]

My dim understanding is that the most efficient, lowest drag, highest flow passage would be a straight port with a circular cross-section.I was compiling a short answer to you in my mind but then I read Wobs answers and I could not have said it any better, not even in dutch.
My short answer would have been that you are completely right about straight ports: they should be circular. But there is nothing straight about a good transfer duct, at least not at the inner curvature, where it counts. If there is, then you are giving away an opportunity to fit in a larger inner radius.

[seattle smitty]

Okay, Peewee's photo is a dramatic example. The parallelogram-shaped B ports look completely wrong, but even the square-ish A ports don't look very good (AGAIN, factors other than making a low-drag port are temporarily set aside here), at least if my intuition is worth a damn.:laugh:

The A ports have very little radius in the corners, so the air flowing in the corners is dragged down badly, which tends to slow the rest of the column excessively. A round port, especially one WITH a low-drag surface, could pass a column of fast-flowing gas with a lot less cross-sectional area than those sharp-edged ports. Since the port is going to make a sweeping turn (Wobbly's teacup handle, maybe), a perfectly circular cross-section is somewhat flattened into an oval. Where do you put these oval-shaped ports? Obviously, you have to put them a little farther away from the cylinder bore, making them follow an even more sweeping turn (bigger teacup handle). This might not add a whole lot to the total volume of the ports-plus-crankcase-plus-backsideofpiston, because the ideally-shaped ports need less cross sectional area to pass the same quantity of gas (if you're worried about that volume at all).

Yep, as a sometimes-flyer of little airplanes, I do get the need to have the short turn, like the top of a wing, exactly right to help the gas column to come out of the port window properly-directed. The best cross-sectional shape for the short turn might NOT mirror the shape of the outside turn, and therefore the oval port might not be symmetrical, outside turn to inside turn. I sure would be interested to see exactly what shape results, once all the variables of the weight of the air/fuel (real racing fuel, hah!), its desired average velocity at best-power, the sweeping turn, etc, etc, were plugged in to my imaginary (??) program for shaping ports. And then what does the transition to the port-window shape look like? Must it really be a long transition, as Wobbly asserts?

As I write this, it sounds even to me like an obsession with minutiae. But getting better and better 2-stroke ports makes a difference. In our outboards, old 3-port designs (meaning two transfers, one boost port) were used until quite recently. The main producers of these engines, Konig and Yamato, probably were getting something near the maximum available from this design. But maybe ten years ago, one of the racers showed up at a national championship with a brand-new Rossi 250cc engine, and proceeded to post lap-times better than all but the top couple of 350cc rigs. Everybody there could see the writing on the wall ("Sell your old junk and buy a new Italian motor").

(I only saw Frits' answer after posting this) (which didn't speak directly to my objection about those tight square, and worse, corners . . . sir?) (As I said somewhere above, Frits, it seems to me that your new engine offers a particularly good opportunity to make room for low-drag port runners, and I doubt they would look anything at all like the ones in Peewee's photo).

(The trouble with these long posts is that I have to then edit and re-edit for ten minutes after I put them up here! Frits, as I recall, we are talking within the realm of your direct professional and educational specialty here. Is there any sort of "cookbook," meaning a technical explanation understandable by laymen, for low-drag cross-sections of gas-flowing ports that are making sweeping corners, and relating this to velocity and so forth???)

[Frits Overmars]

The trouble with these long posts is that I have to then edit and re-edit for ten minutes after I put them up here! Frits, as I recall, we are talking within the realm of your direct professional and educational specialty here. Is there any sort of "cookbook," meaning a technical explanation understandable by laymen, for low-drag cross-sections of gas-flowing ports that are making sweeping corners, and relating this to velocity and so forth???)I know all about long posts (or posts that require a lot of time) and the need to re-edit even before I get to post them for the first time because other people were quicker than me. Sometimes those quicker reactions allow me to lay back and do nothing at all, for which I am grateful.
A cookbook that comes to mind is the classic 'Practical Gas Flow' but if I remember correctly it does not dive very deep into the details you are mentioning.

[senso]

Thanks for the response Frits, I have already seen your remarks about the clogged water passages in the rotax cylinders, and again thanks for the heads up.

Regarding the fact that buying a new cylinder, it would be more expensive, because the idea is to give a new life to an old stock cylinder that a friend of mine has, so buying cylinders is unfortunatelly out of question.
When I have the cylinder with me I will inspect both of them, because he has a good cylinder with just the oval port, and a seized cylinder with the oval plus the auxiliar exhaust port.

[Frits Overmars]

Regarding the fact that buying a new cylinder, it would be more expensive, because the idea is to give a new life to an old stock cylinder that a friend of mine has, so buying cylinders is unfortunatelly out of question. When I have the cylinder with me I will inspect both of them, because he has a good cylinder with just the oval port, and a seized cylinder with the oval plus the auxiliar exhaust port.My thoughts about costs were based on Peewees proposal of cutting the waterjacket open and then welding (and re-nikasiling!).
Regarding your original question about the possibility of adding aux exhaust ducts in a cylinder that has none: I suppose that in the interest of economics Rotax uses the same coolant cores for all types, so there should be sufficient material in the right places. But I never checked....

[wobbly]

4T ports have been studied to death, and the best flowing examples have minimum turn to the valve axis and some have a flat floor giving a D shape to keep
velocity up on the short turn.
But as is described in the classical texts the CSA where the duct turns, is made bigger, and then necks back down to the venturi under the seat.
In a 2T we use the D concept on the short turn , but unlike a 4T where they are trying to get equal flow discharge radially thru the curtain area - and impart swirl, in a 2T we are
trying to achieve different things.
Firstly is to keep the flow accelerating uniformly down the duct length, and secondly direct the flow uniformly so the discharge exits into the cylinder with NO swirl ie a coherent column.
Thus we cant use the expansion theory around the turn, and IF the side walls were parallel at the exit then the best shape would be a rectangle to initiate and then preserve the columnar discharge shape.
But as is mostly the case, the front and rear walls converge radially, so the inner wall is best angled as an average of the two, and the square gets tipped over into a non parallel parallelogram ( whats that called ? ).
I have seen plenty of results from CNC anemometric flow visualising software, and have never seen any evidence that the flow in the corners of the ports is "lagging " behind due to
excessive wall friction.
So it would seem that the current techniques of linear area reduction increasing the velocity, and duct walls that initiate the radial flow directions early on - are the best compromise between raw
flow numbers ( cfm ) Vs a high discharge coefficient with a coherent exit stream.
As always no free lunch.

[peewee]

smitty i dont have a answer why them ktm ducts are shaped the way they are. but im sure ktm is more than capable of designing a better duct that would produce more power. we have to remember the intended purpose of the engine however. sometimes more is less. im not aware of many people that would be sucessful on a motox track with a 80hp bike. ktm could have borrowed a few ideas from the rsa and probly made the bike too powerful to ride on most any track but thats bad for business. without customers you may as well go sit in the welfare line and collect free soup.

so maybe that particular paralellogram type of duct shape doesnt give the most power but it may offer some other advantage and give a better power spread possibly ? just a guess . still its interesting that the latest generation of cr250 had a duct entry shape real similar as well. could ktm and honda be so stupid as to not put a single thought into duct shapes ? i kind of doubt it. but even with its paralellogram shape and sqaure corners, those engines manage nearly 50hp without much tinkering other than some carb adjustments.

if ktm continues their 2t development, which im sure they will, 10yrs from now im sure they will have something better, with less fuel consumption, while still maintaining the same amount of power. i wont mind as the race fuel around here is $10gal for the cheapest stuff

[peewee]

As long as the porting STA numbers are correct for the rpm and you have EVERY other aspect of the design spec'd to suit that rpm then
the higher the rpm the higher the power - as long as the torque holds up for long enough.
In the case of the Banshee style engine I have done designs with peak power at 11,000 and usable overev to 12,000.
With close to 100 RWHp on a Dynojet this is reliable and doable.

.

ive seen a pile of graphs using oem yami cylinders and dont recall any of them making it past 10.5k before the curve falls off. these engines were mostly done by big name shops. if i could do that good or even better i think it would be quit a accomplishment since my work shop is a measly one car garage :2thumbsup

[F5 Dave]

You'd think from what some people say of me I'd be the Devcon king, but if anyone has some better solutions for smearing filler in small transfer ports I'd appreciate it. Actually I've swapped to JB Weld for the mean time as I can't afford more Devcon at this time of year & people use JB successfully in 4 stroke inlets so it can handle the heat.

But I usually use a screwdriver & in an inlet a wet finger will smooth it nicely. But in transfers of 100cc, or worse 50cc barrels getting it in nicely can work some days & be a major rework battle the next. I've even tried small brushes, but not with much success.

I should really heat it some to make it flow like I do in winter, but its warm here now so I haven't been doing so.

Techniques?

[peewee]

if it were me i would probly use the stucco verde stuff. seems like it was $15 for 3' the last time i bought it. thats enough to do quit a few 100cc barells. plus its more like putty instead of a runny mess like jb weld. just dont use it with methanol. theres also some stuff called moroso a+b thats not very expensive and would surely do many 100cc barells. its a 2part putty also. i bought some but havent used it in a engine yet. im thinking it would work great like the stucco verde. probly shouldnt use it for methanol either

can usually find it on ebay for $28 with free shipping

http://www.moroso.com/eb/catalog/navigationPath//1::Moroso%20Performance%20Products/18000::Chemicals/%7B15565%7D::A%20%20B%20Epoxy.html?entryId=catalog .productgroup.118000&expand=true&menuId=main.menu

[peewee]

smitty i think youll agree this honda cylinder looks pretty similar to the previous ktm i posted. A entrance is darn near sqaure. B has the paralellogram type of shape. now if you look at the rear studs on both cylinders, there is more than enough material they could have made the B entrance most any shape they wanted but for some strange reason they chose the shape they did. im stumped as to why. so these shapes may not give the most power but there must be some advantage ? another thing i never found a answer to yet, not that i really care to find the answer either but its one of them things that keeps me scratching my head..... why are all the modern japanese and ktm 250cc engines using the same length rod with 72mm stroke ? hell heres another head scratcher, why do all modern 250cc engine use the 66.4mm x 72mm bore stroke combination ?

[speedpro]

Techniques?

I prep the surface, like you do. I cut a 3mm wide strip from say .8mm mild steel and very carefully bend it to the shape I want the devcon to be. I test this without Devcon by simply fitting it to the port and making adjustments to the shape so the curve matches what I want in the port.

I then jam some Devcon into the port more or less where I want it and then start carefully patting it into shape using my shaped tool. I keep it wet so the devcon doesn't stick and just keep patting away until the devcon is where I want it and the correct shape. Typically there is an amount displaced which can be removed before it dries or I find it easier to let it partially set then lever it out.

I could load a piccy of a couple of tools when I get home. It's too hard to pull up pictures while I'm riding my scooter home.

[Ocean1]

Techniques?

Can you make a devcon mould of the area you want to re-profile that you can subsequently remove from the port?

If so then cut some strips of sheetmetal that you can bend into shapes likely to enable you to deposit devcon over the required area. Use a release agent (glad wrap?) inside the port and then apply the devcon as thick as you can while still being able to extract it. Make some marks in the devcon so that you can re-position it accurately later.

Remove the devcon plug, (I suppose you could use polyester, (bog) and re-shape it as required, it obviously needs to be big enough to cover more than the area to be modified. If you can do it accurately weigh the plug before and after, if not try to get some idea of the volume/mass involved. Clean up inside the port to the usual standard and practice refitting the plug accurately.

The trick then is to apply a little more than the above resin over the port wall, apply release agent to the plug and carefully refit the plug over the fresh resin. When you're happy it's all in the right place slip a condom over the plug and inflate it. With air. 3-4psi should be heaps. You can use silicon lab tubing if you can get sizes that'll work, but you get the idea.

When it's hard pull the lot apart, (even with a good release agent it can take a bit to get the plug out). All going to plan there should be a perfectly shaped port inside there.

[F5 Dave]

I prep the surface, like you do. I cut a 3mm wide strip from say .8mm mild steel and very carefully bend it to the shape I want the devcon to be. I test this without Devcon by simply fitting it to the port and making adjustments to the shape so the curve matches what I want in the port.

I then jam some Devcon into the port more or less where I want it and then start carefully patting it into shape using my shaped tool. I keep it wet so the devcon doesn't stick and just keep patting away until the devcon is where I want it and the correct shape. Typically there is an amount displaced which can be removed before it dries or I find it easier to let it partially set then lever it out.

I could load a piccy of a couple of tools when I get home. It's too hard to pull up pictures while I'm riding my scooter home.
Thanks Mike I'll try that tonight.

[F5 Dave]

Can you make a devcon mould of the area you want to re-profile that you can subsequently remove from the port?

If so then cut some strips of sheetmetal that you can bend into shapes likely to enable you to deposit devcon over the required area. Use a release agent (glad wrap?) inside the port and then apply the devcon as thick as you can while still being able to extract it. Make some marks in the devcon so that you can re-position it accurately later.

Remove the devcon plug, (I suppose you could use polyester, (bog) and re-shape it as required, it obviously needs to be big enough to cover more than the area to be modified. If you can do it accurately weigh the plug before and after, if not try to get some idea of the volume/mass involved. Clean up inside the port to the usual standard and practice refitting the plug accurately.

The trick then is to apply a little more than the above resin over the port wall, apply release agent to the plug and carefully refit the plug over the fresh resin. When you're happy it's all in the right place slip a condom over the plug and inflate it. With air. 3-4psi should be heaps. You can use silicon lab tubing if you can get sizes that'll work, but you get the idea.

When it's hard pull the lot apart, (even with a good release agent it can take a bit to get the plug out). All going to plan there should be a perfectly shaped port inside there.
Thanks but I don't think you could remove the complex shape.

[Ocean1]

Thanks but I don't think you could remove the complex shape.

Murphy strikes again huh?

Not even in pieces?

[AndreasL]

When talking Devcon and the like...

I have this (s*%#)cylinder with way to high transfers (Approx 132-136° AFTER taking 2.3mm of the base surface!).

But I still need to lower the transfers by 1-2 mm roughly.
Gas torch and a skilled welder (not me) most probably will do the trick...but...

Any one have had succsess using any other method to change or reshape an area where we have constant abuse from one or two piston rings running back and forth? To comlicate things even further, as you all know, this part is "edge shaped".

Yes, I know "Get an other barrel!", but this is more or less what is avaible. Really bad manufactured items making performance parts for a SB Chevy look like race ready out of the box. ;)

I'm naive enuff to hope for a simple sollution here. LOL

[senso]

smitty i think youll agree this honda cylinder looks pretty similar to the previous ktm i posted. A entrance is darn near sqaure. B has the paralellogram type of shape. now if you look at the rear studs on both cylinders, there is more than enough material they could have made the B entrance most any shape they wanted but for some strange reason they chose the shape they did. im stumped as to why. so these shapes may not give the most power but there must be some advantage ? another thing i never found a answer to yet, not that i really care to find the answer either but its one of them things that keeps me scratching my head..... why are all the modern japanese and ktm 250cc engines using the same length rod with 72mm stroke ? hell heres another head scratcher, why do all modern 250cc engine use the 66.4mm x 72mm bore stroke combination ?

The technical questions are a bit too much for me, but the 72mm stroke lets them make a 300cc version just changing the cylinder bore, instead of having different cranks for the 250 and 300cc engines they keep all the bottom end equal across the two versions.
Gas Gas, TM and Husaberg do that, and KTM may as well do that "trick".
The rod length might be a compromise between ideal size and not to big that you end with the cylinder in the gas tank.

[Martin1981]

Just thank you for that thread! most interesting thread i ever read! Just one question: can anybody tell me where this chocky fish is available? i googled and can not find it. we only have chocky bananas available here in germany. :confused:


http://fs1.directupload.net/images/141217/temp/wwi74bwm.jpg (http://www.directupload.net/file/d/3839/wwi74bwm_jpg.htm)

[AndreasL]

Answer my self...

The more I think of it the easiest solution would be a resleeve etc etc...or make my own FOS cylinder from scratch.

Using any kind of putty will not work, even if TZ350 has shown the opposite in his ex-port.

Do as Wobs say and fit a reed valve to take care of the to high intake port and live with a to high transfer timing?
Or find that missing welder. Or both.

Crap, this was supposed to be a simple (low state of tune) engine just to have something running untill all crazy ideas can be put in to an other one.

Sorry for the rant, but its frustrating sometimes to know how bad i.e. a cylinder really is. EngMod2t prevents me from doing as "all others" and fit the parts and just ride the thing. Even for a simple engine.

Need to call that welder/brazer.

[seattle smitty]

Martin, thanks for keeping things in perspective here.

Peewee, it's not that I think the factories are "too stupid" to do something different. I'm just askin', same as you. The engineers weren't "stupid" in the mid-60's when everything had three intake ports, and nor were they ten years earlier when the engines were all cross-flows with deflector pistons. But they watch each other, and the state of the art changes by one outfit coming up with a new way of doing things that proves to be effective.

Have we reached the end-point of five-port (A's and B's and BP) 2-stroke development? As I read Jan Thiel, he seems to think so, that even with a clean-sheet design he couldn't do much more with a five-port engine, and that it would take a wholly new breakthrough design (like Frits' FOS) to get 2-stroke development going again. Personally, I'd like to find a little more power (outboards have no traction issue, and can hook up all the power you can find) from a five-port engine (Frits' 24/7 concept is very cool, but will surely be a bugger to get sized and tuned) before throwing in the towel and working on the FOS, which has too damned many exhaust pipes, Frits:laugh:

Wobbly, I've gotta look for something . . . back in a minute, I hope.

[Grumph]

Answer my self...

The more I think of it the easiest solution would be a resleeve etc etc...or make my own FOS cylinder from scratch.

Using any kind of putty will not work, even if TZ350 has shown the opposite in his ex-port.

Do as Wobs say and fit a reed valve to take care of the to high intake port and live with a to high transfer timing?
Or find that missing welder. Or both.

Crap, this was supposed to be a simple (low state of tune) engine just to have something running untill all crazy ideas can be put in to an other one.

Sorry for the rant, but its frustrating sometimes to know how bad i.e. a cylinder really is. EngMod2t prevents me from doing as "all others" and fit the parts and just ride the thing. Even for a simple engine.

Need to call that welder/brazer.

If you can't raise the bridge, lower the river...think outside the box. Taller piston ? longer rod ? Machine the case top face if you can't take more off the barrel.

[F5 Dave]

After my bitching heating the epoxy made it flow better, just work quickly. Mikes bent steel idea had some merit too. You can spend forever inside these crappy 1978 MB100 ports.

[seattle smitty]

Wobbly, my teacher! Triumph! I actually found something! On P. 1023, Oct 23rd, Yow Ling in post #15336 offered "CFD Simulation of 2-Stroke Scavenging" and other goodies by C. Yang 3D. If you don't want to look, this was the sim with the cutaway cylinder that looked like it was running on tomato paste. There are some other nifty sims there, particularly one entitled, "Streamline," that might come close to showing what you are describing if I could just get the thing to run reeeeall sloooww. But I can't, so I have to take your word that the pinched corners of some of these ports appear not to drag down the adjacent A/F fllow. Makes no sense to me, but okaaayy . . . (still dubious).


(wobbly;1130805345]4T ports have been studied to death, and the best flowing examples have minimum turn to the valve axis and some have a flat floor giving a D shape to keep velocity up on the short turn.

(smitty) To keep velocity up, or to keep the flow attached and not turbulent? (probably saying the same thing)

(Wobbly) But as is described in the classical texts the CSA where the duct turns, is made bigger, and then necks back down to the venturi under the seat.

(smitty) Bigger CSA, PLUS a more flattened oval (or more-flattened D-shape, or more flattened rectangle-with-corner-radii) . . . right? This is half of what I'm getting at, as being (I thought) a better shape for the usual 2-stroke transfers as they make the sweeping turn.

(Wobbly) In a 2T we use the D concept on the short turn , but unlike a 4T where they are trying to get equal flow discharge radially thru the curtain area - and impart swirl, in a 2T we are trying to achieve different things.
Firstly is to keep the flow accelerating uniformly down the duct length, and secondly direct the flow uniformly so the discharge exits into the cylinder with NO swirl ie a coherent column.
Thus we cant use the expansion theory around the turn, . . . .

(smitty) "expansion theory"? . . . they want more CSA where the gas flow is taking a turn just so the flow rate will come out the same as in the straight sections of the port, right? wrong?

(Wobbly) . . . and IF the side walls were parallel at the exit then the best shape would be a rectangle to initiate and then preserve the columnar discharge shape.
But as is mostly the case, the front and rear walls converge radially, so the inner wall is best angled as an average of the two, and the square gets tipped over into a non parallel parallelogram ( whats that called ? ).

(smitty) FWIW, the non-parallel parallelogram is a non-symmetrical trapezoid. I thought I recalled it as a rhombus, but it seems they (rhombii? rhombera?) have to be symmetrical, where trapezoids do not. (I looked up quadrilaterals). Anyway . . . I sure wish I knew where/how to find that big-bore engine I referred to above, which evidently is or was a good performer, but differs a little from the more typical arrangement in your description, which I THINK I mostly get. Guys here have referred to the "hook" in the trailing edge of (what I think you are calling) the rear wall (Aprilia ports, I think), and I take it this is one way of getting the front and rear walls to "converge radially" (am I understanding you at all?).

(Wobbly) I have seen plenty of results from CNC anemometric flow visualising software, and have never seen any evidence that the flow in the corners of the ports is "lagging " behind due to excessive wall friction.

(smitty) This is where I wish I could run Yow LIng's sims in ultra slow motion, dang!

(Wobbly) So it would seem that the current techniques of linear area reduction increasing the velocity, and duct walls that initiate the radial flow directions early on . . .

(smitty) That last bit ("initiate early on") is part of what I question, and I don't see how it necessarily follows from the rest of what you've said. Taking four-stroke ports and runners, which as you said have had lots of development, they typically have a bunch of turns, entailing a bunch of shape-changes, from start to finish, even if we can ignore what they have to do to get around a valve head and impart swirl.

(Wobbly) . . . are the best compromise between raw flow numbers ( cfm ) Vs a high discharge coefficient with a coherent exit stream.
As always no free lunch.[/QUOTE]

(smitty) "discharge coefficient"? Just a dumb liberal arts major, y'know.:wacko:

As always, I appreciate your kindly efforts and patience as you cast your pearls . . . :sweatdrop

[F5 Dave]

http://thetoastieproject.com/2013/07/15/chocolate-fish/ OTE=Martin1981;1130805850]Just thank you for that thread! most interesting thread i ever read! Just one question: can anybody tell me where this chocky fish is available? i googled and can not find it. we only have chocky bananas available here in germany. :confused:


http://fs1.directupload.net/images/141217/temp/wwi74bwm.jpg (http://www.directupload.net/file/d/3839/wwi74bwm_jpg.htm)[/QUOTE]
ThE wonders of google. Results vary from country to country.

ahh crap i tried to post a link but tablet is a dog and i missed. At start of post

[AndreasL]

If you can't raise the bridge, lower the river...think outside the box. Taller piston ? longer rod ? Machine the case top face if you can't take more off the barrel.

Have done all that and yesterday I thought I hade it solved by using a different piston. But I was wrong.

Called my my welder and he will have a look. Think he will solve it just fine.

Thanks for the input and support though.

[peewee]

frits it seems like one time you said if your FOS was upscaled to 125cc it would have even more power than rsa. do you have any predictions how much it would have ? if it was scaled even further to 250cc ?

[peewee]

how you reckon this thing would fire. outside cylinders at the same time and middle cylinder 180* off ?

[wobbly]

Being " just " an RZ with another tacked on one end it will be all 120 apart I suspect - easy to do with a jig as the crank isnt keyed
on the main axles.
Firing two together would be primary vibration balance suicide without a balance shaft.
Trust me I know, the BSL fired one end and the middle together, with 120 V angle and a balance shaft.
Very smooth, but busted cranks due to torsional twist, even taking the drive off between 2 & 3

[F5 Dave]

Taking drive between 2&3?. Don't suppose you have pics of that?

[Frits Overmars]

frits it seems like one time you said if your FOS was upscaled to 125cc it would have even more power than rsa. do you have any predictions how much it would have ? if it was scaled even further to 250cc ?The whole project would be futile if it would not outperform the RSA. From the point of view of the various angle.areas it should be able to rev about 20% higher than the RSA without running out of breath (and let's hope we can build a con rod bearing that will play along).
Estimating the scavenging efficiency is not so clear-cut. Of course I hope that it will reach the RSA's benchmark level (and sometimes I have wet dreams of beating the RSA's level thanks to a blowdown flow with less energy losses) but even if it loses 10%, I will still have a 10% power advantage.
Similar considerations should be valid when scaling the system up to 250 cc or whatever size you like.

[Martin1981]

I hope this system will work some day. but luc foekemas experience with it is not very encouraging yet.

https://www.facebook.com/notes/luc-foekema/fst-twostroke-design/4080202582494

one thing i do not like so much.....2 pipes are needed. no KISS. Frits, luc seems not to be your very best friend or is it just a feeling?:bleh::msn-wink:

[Haufen]

Seems like there is no inner radius on the transfers of Luc's cylinder.

[breezy]

can you imagine how precise the transfer port flow/direction/speed would need to be to produce optimum cylinder filing and also the exhaust characteristics to achieve such an engine. bad enough with what we have now, maybe have to rewrite most of the 2t tuning as we know it today!:shit:

[F5 Dave]

But think of the revs.

So what we need is for Frits to quickly sell the completed design to KTM who then for some unfathomable reason decides to put it into production as a 100cc road bike with their supposed 'ready to race' philosophy.And sell thousands of them, particularly in the Southern hemisphere.

Then I need to wait a few years so I can afford one. All this needs to happen before I'm too old to race competitively. . . . Which was probably a few years ago anyway. I'm a slow learner, I think I got to my peak when I was 40. It doesn't seem like that long ago.

[peewee]

hey guys since just recently i started working with the small cylinders i figure its good to upgrade to smaller tools also. today i recieved a smaller 90 handpiece and it looks perfect for the job :Punk:. my full collection is getting bigger

[senso]

Interesting angle head, is that an eBay cheapie or is it for the cc specialty tool guys?

[peewee]

i dont bother with cheap crap from china :laugh:. i got it from ccspecialty because they had the best price i could find but you can get it from other places aswell. i dont believe cc makes any of the tools but rather just distributes them. its nakanishi head. not exactly sure who makes the shaft handle

[F5 Dave]

Jealous, was looking at them just yesterday, but will have to wait. I get quite some chatter with my 3mm dentist setup with larger bits adapted & its isn't quick or precise as it could be. But the money isn't there atm.

[peewee]

why not use a credit card then pay it back in 2 or 3 payments ? if i paid cash upfront for everything, i would have almost nothing :laugh:

[Flettner]

But think of the revs.

So what we need is for Frits to quickly sell the completed design to KTM who then for some unfathomable reason decides to put it into production as a 100cc road bike with their supposed 'ready to race' philosophy.And sell thousands of them, particularly in the Southern hemisphere.

Then I need to wait a few years so I can afford one. All this needs to happen before I'm too old to race competitively. . . . Which was probably a few years ago anyway. I'm a slow learner, I think I got to my peak when I was 40. It doesn't seem like that long ago.

What bore size would you need 51mm bore , 51mm stroke? Whats max oversize for 100cc water cooled?

[jasonu]

Just thank you for that thread! most interesting thread i ever read! Just one question: can anybody tell me where this chocky fish is available? i googled and can not find it. we only have chocky bananas available here in germany. :confused:


http://fs1.directupload.net/images/141217/temp/wwi74bwm.jpg (http://www.directupload.net/file/d/3839/wwi74bwm_jpg.htm)

Husaberg has a cupboard full of them. He is always lurking around this forum so tracking him down will be easy.

[husaberg]

Husaberg has a cupboard full of them. He is always lurking around this forum so tracking him down will be easy.

husaberg, it should be noted is spelt with a small h as I don't like to show off...
I haven forgotten I owe you a few still for running the Northern Hemisphere Sprocket forwarding operation.........:psst:
So are Chock fish still just a NZ thing?

Anyway anyone got some decent pic of the Konig flat 6 I guess it wasn't one disk valve like the Four? King Konig I think it was called
Seattle Smithy?

[speedpro]

What bore size would you need 51mm bore , 51mm stroke? Whats max oversize for 100cc water cooled?

If you were building one for Richban you'd start at 54x54

[F5 Dave]

Erm 104cc if I was to stay legal. Oh right

[Flettner]

Erm 104cc if I was to stay legal. Oh right

Then perhaps 50mm bore and 51mm stroke.
I've got this sleeve cylinder crank case underway again, should have the top and bottom patterns ready this weekend. and although it's to suit a YZ250 gearbox I was thinking about making an FOS cylinder ( after the sleeve idea turns to shit? ) to fit on this same case. 51mm stroke will fit no problem, case reed ( V force ) and transfers everywhere around the crank case.
How does the FOS cylinder run under the power band ( off the pipes )? Could we do some tricks to help this part of the rev range?
128 transfers, 195 exhaust? Somewhere to start?

[husaberg]

Then perhaps 50mm bore and 51mm stroke.
I've got this sleeve cylinder crank case underway again, should have the top and bottom patterns ready this weekend. and although it's to suit a YZ250 gearbox I was thinking about making an FOS cylinder ( after the sleeve idea turns to shit? ) to fit on this same case. 51mm stroke will fit no problem, case reed ( V force ) and transfers everywhere around the crank case.
How does the FOS cylinder run under the power band ( off the pipes )? Could we do some tricks to help this part of the rev range?
128 transfers, 195 exhaust? Somewhere to start?

I am no physicist but I think the FOS will need to run constantly in its power band so require a cvt?

Wouldn't we rather have a 500cc V4 Neil?..........

[F5 Dave]

I have a clutch lever and know how to use it.

Actually if I have any skill, its in degrading transmission fluid with brutal but beautiful clutch plate degradation from over quarter of a century of 50cc racing.

[husaberg]

I have a clutch lever and know how to use it.

Actually if I have any skill, its in degrading transmission fluid with brutal but beautiful clutch plate degradation from over quarter of a century of 50cc racing.

I think you missed my point I am not doubting you ability to take maters into your ownhands
I am suggesting that I don't think it will run at all below 10,000-11,000rpm

[F5 Dave]

Either does my 50. Your point?

[AndreasL]

This starts to get really interesting, dissecting the FOS concept.

I'm all ears and cant wait for Frits to join in. :corn:

[husaberg]

Either does my 50. Your point?

Not doesn't run well.......... What I am suggesting is will not run at all!.......

[TZ350]

Well over the last 6 months several 50's setup and track ready and the 50 Chambers was sorting for Av is running and Av's 125 is behaving itself and has given up drinking its gearbox oil so we now have time to re visit the EFI project.

306775

When we Popped the head off I was expecting to see a damaged piston after all the hours of detonation on the dyno but all there was, was a mark from where the piston has been kissing the head. If I skim a bit from the squish area in the head it all should be fine.

306773

The next step in the EFI project is to get good at controlling the endpoint of the injection cycle with some precision.

I want to see if we can make the injection cycle fit inside the time window of the transfer port opening. There are two logical injectors, a small one for starting and low speed running up to when the engine starts to get onto the pipe at about 8,000rpm and then a pair of larger secondary injectors take over when the engine is making real power.

306771 306772

Flettner suggested to me using a solenoid coil and ignition trigger coil combo. The basic idea is to wrap the two together so they are magnetically coupled.

With the fuel injector timed by the original ignition trigger coil and the solenoid coil driven by a fuel injector lead. The solenoid then excites the ignition ignition trigger coil to fire the ignition. This way with the help of an ignition timing light you can see where abouts in the crank cycle the EFI is firing the fuel injector.

The Ecotrons software has a map that allows you to chose the endpoint of the injection cycle.

If I start off with the EFI and Ignitec ignition maps set at TDC then I can use the timing light to follow the changes in the fuel injection end point map.

The idea is to avoid wasting fuel with the first part of the scavenging air that is lost out of the exhaust port.

306776

With the head off I will be able to exactly time the injection endpoint to the transfer closing time. That way I hope to adjust the fuel injection cycle to coincide with the airflow through the transfer port that is actually trapped in the cylinder.

The biggest problem is that at engine speeds above 8-9,000rpm you are rapidly getting short of time to fire sufficient fuel into the part of the transfer stream that is going to be trapped in the cylinder and at 14,000rpm time has becoming critical.

306774

The inlet is open for nearly twice as long as the transfers.

So if I can't find enough time at the transfer port for both high and low speed injectors I will move the high speed secondary power injector(s) to the inlet so they squirt directly down the inlet throat.

The smaller primary injector runs till about 8,000rpm and with it still in the rear boost port I should be able to keep the engine running clean at lower rpm and as it gets up onto the pipe I expect the resonant stuffing action of the pipe at higher RPM will reduce the amount of fresh air and fuel lost out of the exhaust port from the inlet throat injectors.

A carburettor mixes fuel with all the air that passes through it. So with the inlet injector what I don't want to end up with is patches of air that have no fuel in it.

[Frits Overmars]

I get quite some chatter with my 3mm dentist setup with larger bits adapted & its isn't quick or precise as it could be. But the money isn't there atm.Stay away from this dentist stuff, unless you can get it for free. Doing one 125 cc cylinder once took me five dentist sets. When the cylinder was ready, all five sets were binnable. The bevel gears and bearings are just not up to the job.
If you can afford it, look for a hand tool with a swiveling head. I can't find a picture so I will try to describe it: there is a 30° kink at the business end of the handgrip. The right-angled head can swivel around the kinked axis, so the angle between the handgrip and the cutter can vary from anything between 60° and 120°.


can you imagine how precise the transfer port flow/direction/speed would need to be to produce optimum cylinder filing and also the exhaust characteristics to achieve such an engine.It won't be any different from what we are used to, Breezy. On the flow bench the central scavenging column created by the six incoming transfer streams has proven to be very stable; even if I blocked one of the transfer ducts completely, that column remained intact, albeit off-centre. And the exhaust characteristics depend on the gas dynamics in the pipe. The gas will be the same, the pipe proportions will be the same, so the pipe behaviour and the engine characteristics will be the same.


I've got this sleeve cylinder crank case underway again, should have the top and bottom patterns ready this weekend. and although it's to suit a YZ250 gearbox I was thinking about making an FOS cylinder ( after the sleeve idea turns to shit? ) to fit on this same case. 51mm stroke will fit no problem, case reed ( V force ) and transfers everywhere around the crank case. 128 transfers, 195 exhaust? Somewhere to start?Here:
http://www.pit-lane.biz/t117p318-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked
http://www.pit-lane.biz/t117p333-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked
(it took me over an hour to find those links; I think I should cut back on my forum activities. Which one should I drop first? :p)


How does the FOS cylinder run under the power band (off the pipes)?Like any other pipe resonance-dependent two-stroke.


Could we do some tricks to help this part of the rev range?Sure, also like on any other pipe resonance-dependent two-stroke: programmable ignition, power jet, power valves, trombone pipe.
But since I am under the impression that you can build anything you can think of: how about shrouds in the transfer roofs? If you lower them, you will lower the transfer timing, so wrongly-timed exhaust pulses will have less chance of shoving fresh cylinder charge back into the transfer ducts. Moreover, lowering the transfer timing while leaving the exhaust ports alone will increase the blowdown angle.area. That will put an end to the dreaded part-throttle detonation that plagued all Aprilia racing engines.
Taking this thought a little further, you could even use the movable transfer ceiling instead of a throttle.


I am no physicist but I think the FOS will need to run constantly in its power band so require a cvtI am, and I wonder why you would think so. Like I mentioned above, the engine character will be no different from what we're all used to at the moment.
Having said this, I am all in favour of CVTs.

[seattle smitty]

Then I need to wait a few years so I can afford one. All this needs to happen before I'm too old to race competitively. . . . Which was probably a few years ago anyway. I'm a slow learner, I think I got to my peak when I was 40. It doesn't seem like that long ago.

High fives from here, Dave, I can identify all too well; if I wasn't laughing so hard, I might cry.

Peewee, I like the look of that Japanese handpiece. What looks good is the small size and design of the head that will allow the working end of the rotary file to sit a lot closer to the centerline of the handle, which should reduce chattering. Will it run off the Foredom flex-shaft like the other handpieces in the second photo, all of which I assume are from CC Specialty because that's where I got mine (in the early '70s)? What are the extra goodies in the kit?
One thing that's good to have is a reversible drive-motor, because sometimes where you get into areas that cause uncontrollable chatter you can use reverse-twist rotary files and run the motor in reverse, and solve the chatter problem. I was very happy when somebody told me about that, back in the day. Peewee, I hope the bevel gears have a bit less lash than those in the CC Specialty unit (you want to disassemble the head and lube those occasionally).


husaberg-with-a-small-h, pay attention, it's Smitty, s-m-I-T-T-y, American-style with two t's, not "Smithy." Anyway, I never heard that project called the "King Konig," but Dieter Konig (with umlaut) showed up with it at a big race in Texas some time in the early '70s. It was a one-off, which he made from one of his class D (about 700cc) flat-four motors and half of another, for something close to 1000cc or 1100cc (there was a rule change about that time) which was what we called F class I those days. FWIW, I was one of a few guys around the US who wanted to drop the old M/A/B/C/D/E/F designations (the M was for "Midget": 125cc), and change to the cubic centimeter designations which the Japanese motorcycle invasion had made common parlance; I like to think that an essay I wrote had some influence on the matter, and that another essay influenced the authorities' decision to drop the requirement to run engines they approved, thus opening the opportunity to adapt engines from bikes, sleds, etc., to outboard racing.

Anyway, I only saw a few photos of that F Konig flat-six, which IIRC ran well but went back to Berlin and wasn't run again. Pretty sure it had a single big rotary valve with three holes, three carbs. There were other home-brew projects of a similar nature, with two class C (500cc) powerheads stacked up, or set side-by-side on a gearbox. They sometimes made tons of power, had many teething problems, and generally were abandoned fairly soon, usually because they were very hard on lower units. Also heavy. I'll see if I can link you to some pix.

Dieter Konig was a talented man who supplied racing outboards that gave a lot of people including me a lot of good times. Some of the workmanship was not quite the best, and Konig fell well behind the state of the art in 2-stroke design by the mid-seventies, but his engines were affordable. As you guys know, he was involved with motorcycle racing for a couple of years, and with side-car racing for longer and with more success. Helmut Fath built his own GP engines that ran well as I understand, and it looks like they were modeled on Konig's flat-fours, which had first appeared (as outboards) in about 1965. Konig also built some little motors for ultralights, but unfortunately was killed flying one.

[jasonu]

So if I can't find enough time at the transfer port for both high and low speed injectors I will move the secondary power injectors to the inlet so they squirts directly down the inlet throat.

The smaller primary injector runs till about 8,000rpm and with it still in the rear boost port I should be able to keep the engine running clean at lower rpm and as it gets up onto the pipe I expect the resonant stuffing action of the pipe at higher RPM will reduce the amount of fresh air and fuel lost out of the exhaust port from the inlet throat injectors.

A carburettor mixes fuel with all the air that passes through it. So with the inlet injector what I don't want end up with patches of air that have no fuel in it.

Will all of these injectors and carbs added together still be under the class rule of not more than a 24mm carb for air cooled 125 2 stroke motors?

[Drew]

Will all of these injectors and carbs added together still be under the class rule of not more than a 24mm carb for air cooled 125 2 stroke motors?

Gets it's air through a 24mm hole. Legal as fuck.

[F5 Dave]

Thanks Frits, these Chinese mechanical driven heads (for supply to 3rd world dentist I presume) are close to free. I lube the bevel and keep my finger on the head and stop to cool it between blocks of ally. But its a fools errand. Maybe after my 20 year old leathers get replaced I'll get something from CC.

[F5 Dave]

TZ I wonder about oil supply and I'm going to try to spell homogeneity of the mix considering Wobs `already in the transfers` supply of gas. But I do think the testing is cool.

[TZ350]

I am all in favour of CVTs.

306778

Possible water cooled 40hp 100cc 4T turbo and supercharged intercooled water injected CVT project. Or run as is, 150cc H2O 4T CVT.

306779

Future 2T 100cc H2O CVT project using a RG400 cylinder and KT100 piston. The engine/chassis could be made into a simple sidecar or the engine/transmission adapted to a solo chassis. Team ESE have a collection of 50 and 100cc 2T scooter CVT's and when we have cleared the current projects (if ever) we would love to do something with them.

[TZ350]

Will all of these injectors and carbs added together still be under the class rule of not more than a 24mm carb for air cooled 125 2 stroke motors?

Hi Jasonu, I don't understand, so what exactly is the difference between a 24mm carb and its jets compared to a 24mm EFI throttle body and its injectors.

Anyway my Injectors collectively have a smaller total orifice size than the 24mm OKO carbs jets, sorry but I just don't understand what you mean.


TZ I wonder about oil supply and I'm going to try to spell homogeneity of the mix considering Wobs `already in the transfers` supply of gas. But I do think the testing is cool.

Yes I am not to sure about the oil supply or homogeneity of the mixture either. Its all a bit experimental but on the dyno even with transfer injection at big rpm there was some small blowback of fuel out of the throttle body, so hopefully oiling may not be a problem.

The motivation for EFI was to try and get some direct under the piston crown cooling and to overcome the fuel pooling in the plenum that I was getting with an external carburetor.

306780

If I can get the EFI thing working then we will be re visiting the plenum idea on the new 30+hp engine as the plenum with EFI will allow a very big, very short inlet tract. I will still use Flettners ball valve throttle but this time the 24mm orifice will be on the plenum inlet.

Previous experience with the plenum has suggested that the plenums resonance can be adjusted to selectively plump up a portion of the torque curve. A trombone Plenum and Exhaust pipe could have very interesting possibilities. We have the Ignitec engine management system to do the job and a small generator for enough power, so interesting possibilities.

[husaberg]

I am, and I wonder why you would think so. Like I mentioned above, the engine character will be no different from what we're all used to at the moment.
Having said this, I am all in favour of CVTs.
I know you are Frits, ;)tis exactly why I worded it as such, As for the why... it is based on a few posts (I think on Pitlane) where it seems to me anyway that you alluded it would, In hindsight maybe you were actually referring to the open all hours?

[Flettner]

Thanks Frits, I might just do that.

[F5 Dave]

Air cooled engines are fuel cooled as well. A well placed injector would be fair sport and good for LE Brg lube.

[Drew]

Air cooled engines are fuel cooled as well. A well placed injector would be fair sport and good for LE Brg lube.

Even more so given that it's under pressure with EFI. So an injector pointing straight at the bottom of the piston could be an idea to trial. Fuel would vapourise real nice on contact too.

[peewee]

Peewee, I like the look of that Japanese handpiece. What looks good is the small size and design of the head that will allow the working end of the rotary file to sit a lot closer to the centerline of the handle, which should reduce chattering. Will it run off the Foredom flex-shaft like the other handpieces in the second photo, all of which I assume are from CC Specialty because that's where I got mine (in the early '70s)? What are the extra goodies in the kit?
One thing that's good to have is a reversible drive-motor, because sometimes where you get into areas that cause uncontrollable chatter you can use reverse-twist rotary files and run the motor in reverse, and solve the chatter problem. I was very happy when somebody told me about that, back in the day. Peewee, I hope the bevel gears have a bit less lash than those in the CC Specialty unit (you want to disassemble the head and lube those occasionally).
.


all my handpieces (even the new one) use a foredom flexshaft sr series motor with foot pedal speed control. its very powerful and has forward/reverse. i use reverse nearly as much as forward and for that reason i wouldnt even consider owning a motor without reverse. also i have a few reverse spiral carbide bits which i use frequently.

i havent bought much from cc, just the new 90 handpiece and 3 or 4 of the bits. everything else was bought at other places. the two straight handpieces are foredom, the larger 90 is from germany and fully servicable as it can be taken apart and bearings oiled and bevel gears greased. the new 90 is supposed to be a sealed unit with no further lubrication needed but obviously it can be taken apart if you wanted. when its worn out i suppose you send it back to nakanishi for a replacement of the bevel gears and bearings. since this stuff is just a hobby for me its unlikely ill wear out any of these tools anytime soon. some of them ive had for several years and they still work like new. if you go with high qaulity stuff it will last many years

while im thinking of it, whats everyones preference for texture on the walls ? ive heard alot of various opinion on this subject, mostly from noobs that dont know much, so i figured i would ask the experts here. ive always just used the carbides and pretty much left that texture on the walls but maybe theres something better ?

[TZ350]

Air cooled engines are fuel cooled as well. A well placed injector would be fair sport and good for LE Brg lube.


Even more so given that it's under pressure with EFI. So an injector pointing straight at the bottom of the piston could be an idea to trial. Fuel would vapourise real nice on contact too.

That is pretty much what I have been trying to achieve with the upwards directed injection stream from the central injector.

306783 306782

The central injector is aimed at the underside of the piston crown through a slot in the piston. If I have to replace the main outside transfer injectors because of time considerations with a larger single one in the inlet port I will still try and retain this smaller center injector in the rear transfer port.

[Flettner]

It won't be any different from what we are used to, Breezy. On the flow bench the central scavenging column created by the six incoming transfer streams has proven to be very stable; even if I blocked one of the transfer ducts completely, that column remained intact, albeit off-centre. And the exhaust characteristics depend on the gas dynamics in the pipe. The gas will be the same, the pipe proportions will be the same, so the pipe behaviour and the engine characteristics will be the same.

Here:
http://www.pit-lane.biz/t117p318-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked
http://www.pit-lane.biz/t117p333-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked
(it took me over an hour to find those links; I think I should cut back on my forum activities. Which one should I drop first? :p)

Like any other pipe resonance-dependent two-stroke.

Sure, also like on any other pipe resonance-dependent two-stroke: programmable ignition, power jet, power valves, trombone pipe.
But since I am under the impression that you can build anything you can think of: how about shrouds in the transfer roofs? If you lower them, you will lower the transfer timing, so wrongly-timed exhaust pulses will have less chance of shoving fresh cylinder charge back into the transfer ducts. Moreover, lowering the transfer timing while leaving the exhaust ports alone will increase the blowdown angle.area. That will put an end to the dreaded part-throttle detonation that plagued all Aprilia racing engines.
Taking this thought a little further, you could even use the movable transfer ceiling instead of a throttle.

.

You would need fuel injection BUT constant flow type NOT pulsed. I think an electronicly controled constant flow in the inlet might be the way, if using the transfer ports to throttle.
Or maybe six pulsed transfer port injectors? With a power jet type thingy in the inlet at full throttle?

[TZ350]

A Piezo injector may be the answer to the problem of only having a very limited time window available for the injection cycle at 14,000rpm on a 2T because ""a piezo actuator acts up to 5 times faster than a standard injector solenoid "" http://www.dieselhub.com/tech/piezo-injectors.html and are currently used on diesels so they can have several injection events in quick sucesion. Increasingly common on diesels but I have not been able to find any petrol ones I could buy yet.

http://www.germanautocenter.com/blog/audi/engine-direct-injection-in-german-cars/ "With the advent of piezo injectors, engine developers can now inject fuel into a cylinder’s combustion chamber in just 0.2 milliseconds." at 0.2ms they are a whole lot faster than the 2ms minimum on time injectors I have now.

[husaberg]

husaberg-with-a-small-h, pay attention, it's Smitty, s-m-I-T-T-y, American-style with two t's, not "Smithy." Anyway, I never heard that project called the "King Konig," but Dieter Konig (with umlaut) showed up with it at a big race in Texas some time in the early '70s. It was a one-off, which he made from one of his class D (about 700cc) flat-four motors and half of another, for something close to 1000cc or 1100cc (there was a rule change about that time) which was what we called F class I those days. FWIW, I was one of a few guys around the US who wanted to drop the old M/A/B/C/D/E/F designations (the M was for "Midget": 125cc), and change to the cubic centimeter designations which the Japanese motorcycle invasion had made common parlance; I like to think that an essay I wrote had some influence on the matter, and that another essay influenced the authorities' decision to drop the requirement to run engines they approved, thus opening the opportunity to adapt engines from bikes, sleds, etc., to outboard racing.

Anyway, I only saw a few photos of that F Konig flat-six, which IIRC ran well but went back to Berlin and wasn't run again. Pretty sure it had a single big rotary valve with three holes, three carbs. There were other home-brew projects of a similar nature, with two class C (500cc) powerheads stacked up, or set side-by-side on a gearbox. They sometimes made tons of power, had many teething problems, and generally were abandoned fairly soon, usually because they were very hard on lower units. Also heavy. I'll see if I can link you to some pix.

Dieter Konig was a talented man who supplied racing outboards that gave a lot of people including me a lot of good times. Some of the workmanship was not quite the best, and Konig fell well behind the state of the art in 2-stroke design by the mid-seventies, but his engines were affordable. As you guys know, he was involved with motorcycle racing for a couple of years, and with side-car racing for longer and with more success. Helmut Fath built his own GP engines that ran well as I understand, and it looks like they were modeled on Konig's flat-fours, which had first appeared (as outboards) in about 1965. Konig also built some little motors for ultralights, but unfortunately was killed flying one.


Smitty without an h this is all I could find.
http://quincylooperracing.us/subpage112.html
3067896
3067904

Fath
306813

[Flettner]

Look at those nice drum valve throttles.

[TZ350]

306799

American tether car racing http://www.amrca.com/

Jennings 2T tuners Handbook. http://www.amrca.com/tech/tuners.pdf

Lots of interesting little 2T & 4T handmade motors http://www.onthewire.co.uk/epitbx3.htm

[Frits Overmars]

If I can get the EFI thing working then we will be re visiting the plenum idea on the new 30+hp engine as the plenum with EFI will allow a very big, very short inlet tract.As long as that tract is not as short as it could be, I will call it long.
http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=306810&stc=1&thumb=1&d=1419079180and don't tell you won't be able to get to that top disk cover bolt :msn-wink:.


this time the 24mm orifice will be on the plenum inlet.Where else? Imagine that you are in a test cabin and the total air entrance to the cabin is a 24 mm orifice. You can be sure that the air flow through that orifice will be 24/7, not just 220° out of every 360 crankshaft-degrees. That's 60% better...


Previous experience with the plenum has suggested that the plenums resonance can be adjustedIt can be, but this will inevitably mean that there will be circumstances where the resonance works against the engine rather than with it.
With EFI you don't need to worry about fuel dropping out of the mixture due to too low a flow velocity, so make that plenum a big as you can; think Samsonite.

[Frits Overmars]

A carburettor mixes fuel with all the air that passes through it. So with the inlet injector what I don't want to end up with is patches of air that have no fuel in it.If a carburettor has one advantage over fuel injection, this is it.
When the quantity of fuel is controlled via the open/shut time of an injector, it is practically impossible to create a homogeneous mixture at the injector. And I'm not even talking about vaporized fuel here; I'm just talking about every part of air getting the same number of fuel droplets.
Fortunately for us much of the necessary homogenisation takes place in a two-stroke's crankcase, with the con rod stirring things up and transferring its heat to the yet-unvaporized fuel droplets. But with direct fuel injection you loose this advantage, and the con rod bearing looses most of its cooling.


You would need fuel injection BUT constant flow type NOT pulsed. I think an electronicly controled constant flow in the inlet might be the way, if using the transfer ports to throttle. Or maybe six pulsed transfer port injectors? With a power jet type thingy in the inlet at full throttle?Keep it simple, Neil. Spraying a constant flow of fuel in the inlet will do fine. I've been doing some work on 6,5 cc engines (google F3D and MB40) and since those little bastards rev to 36.000 there was no chance in hell that I would find injectors small enough and fast enough, so I designed a constant-flow injection; really simple, with an electric motor driving a gear pump and a spring-loaded conical-seat injector that would open according to the pump yield.
The pump is no problem: they are readily available for people building there own miniature jet engines. Controlling the pump rpm was less easy because the motor that comes with the pump, simply won't run slowly enough. Those litte jet engines are real guzzlers, even compared to a two-stroke, and the motor's stall rpm would still drown our piston engine while we were trying to start it.
Stepper motors were out because their bearings could not handle the gyroscopic forces in an F3D-airplane cornering at over 40g, and because stepper motors can miss steps without giving any feedback other than the engine running too lean. So I had to pulse-width-modulate the original pump motor in order to keep it running at a low, but to all intents and purposes regular rpm. I tried to measure its rpm by having a Hall sensor look at the teeth of the pump gears, but the teeth were so fine that the sensor couldn't distinguish them. The solution was to drill a small number (say 4) holes in the gear flank and have a Hall sensor look at those.
This is where the project came to a halt because of other, more pressing activities. But it may give you something to go by.

[peewee]

hey wobbly i been changing up the numbers alittle on engmod for a bit more power and rpm on this yami engine. first order of business is sorting out the intake area which needs to be bigger. the 2 main windows are fairly tall now but could be made taller still if need be. however i was thinking it would be better to try and gain as much of the extra area from enlarging the boyesens, then if the total intake area is still a bit small i can raise the main windows further as needed. what do you think ?

reason for my thinking is because it will put more of the intake area down lower near bdc, rather than sky jacking the main windows. plus the larger boyesens would help fill up the transfers faster. maybe im wrong here but this seems to make the most sense to me

[TZ350]

I will still use Flettners ball valve throttle but this time the 24mm orifice will be on the plenum inlet.Where else? Imagine that you are in a test cabin and the total air entrance to the cabin is a 24 mm orifice. You can be sure that the air flow through that orifice will be 24/7, not just 220° out of every 360 crankshaft-degrees. That's 60% better...

306814

LOL ... English is a funny thing ... I meant that the 24mm restriction that can currently be seen in the inlet tract of the Flettner ball valve will be re located to the plenum inlet. In the plenum configuration the 24mm restriction has always been in the plenum inlet. 24/7 flow through the regulation 24mm restriction was the whole point of the plenum concept.

EngMod2T suggests 3L is a good size for the plenum, 2L is minimum. Currently its 1L and when I tried it, it gave a significant boost to the lower part of the torque curve but the higher rpm part of the curve was suppressed. That gave me the idea that a variable plenum volume could be very useful too and with the Suzuki GP cases that would be reasonably easy to do.

[wobbly]

Yes, its way better to enlarge the Boyesens as they dont have any flow disruption from the piston.
There is plenty of room to cut away the floor and angle the flow down into the transfer duct feed area in the case.
Example of Cheetah cylinder, the Boyesens are 25 high by 14 wide.

[Flettner]

If a carburettor has one advantage over fuel injection, this is it.
When the quantity of fuel is controlled via the open/shut time of an injector, it is practically impossible to create a homogeneous mixture at the injector. And I'm not even talking about vaporized fuel here; I'm just talking about every part of air getting the same number of fuel droplets.
Fortunately for us much of the necessary homogenisation takes place in a two-stroke's crankcase, with the con rod stirring things up and transferring its heat to the yet-unvaporized fuel droplets. But with direct fuel injection you loose this advantage, and the con rod bearing looses most of its cooling.

Keep it simple, Neil. Spraying a constant flow of fuel in the inlet will do fine. I've been doing some work on 6,5 cc engines (google F3D and MB40) and since those little bastards rev to 36.000 there was no chance in hell that I would find injectors small enough and fast enough, so I designed a constant-flow injection; really simple, with an electric motor driving a gear pump and a spring-loaded conical-seat injector that would open according to the pump yield.
The pump is no problem: they are readily available for people building there own miniature jet engines. Controlling the pump rpm was less easy because the motor that comes with the pump, simply won't run slowly enough. Those litte jet engines are real guzzlers, even compared to a two-stroke, and the motor's stall rpm would still drown our piston engine while we were trying to start it.
Stepper motors were out because their bearings could not handle the gyroscopic forces in an F3D-airplane cornering at over 40g, and because stepper motors can miss steps without giving any feedback other than the engine running too lean. So I had to pulse-width-modulate the original pump motor in order to keep it running at a low, but to all intents and purposes regular rpm. I tried to measure its rpm by having a Hall sensor look at the teeth of the pump gears, but the teeth were so fine that the sensor couldn't distinguish them. The solution was to drill a small number (say 4) holes in the gear flank and have a Hall sensor look at those.
This is where the project came to a halt because of other, more pressing activities. But it may give you something to go by.

Yes I'm familiar with pulse width modulation, most car / motorbike electric throttles work like this. It's how my 360 RV throttle needs to work. I think the LINK ecu will drive this as an injector.

[Martin1981]

Wobbly, i have a question regarding the reed setup you posted once.

you said, that one should use the softest carbon reeds that one can find. i have reeds of 0,25 mm thickness. is that ok or too thin?
and can i use the 0,25 mm thick carbon material for the revplates and the backupplates also? thanks.

[mr bucketracer]

Wobbly, i have a question regarding the reed setup you posted once.

you said, that one should use the softest carbon reeds that one can find. i have reeds of 0,25 mm thickness. is that ok or too thin?
and can i use the 0,25 mm thick carbon material for the revplates and the backupplates also? thanks.306864the hulk is a 2 stroke

[TZ350]

<iframe width="420" height="315" src="//www.youtube.com/embed/fPeyhiD7KYw" frameborder="0" allowfullscreen=""></iframe>

How the Rocket Three is built. I like their approach to the small details, like handling and lunch breaks.

[TZ350]

.

The last roll of the Dice.

Sat down and took some time over checking out the EFI injection end angle.

306882306887

First step was to set the Ignitec up so it had zero advance and then magnetically connect a spare trigger for the Ignitec to a solenoid coil energised by the pulse from the EFI as it fires an injector.

The EFI is triggered of the original rotor ignition timing trigger and the EFI in turn triggers the Ignitec and timing light so we should be seeing the true timing of the EFI injection cycle. By swapping the solenoid wires I can see the injection start and end point.

With the wires the right way around I can easily see when the EFI is ending an injection cycle.

306885306881306883

Next step was to position the piston at different places, mark the flywheel with a marker pen and then use a timing light to see whats happening and then adjust the Injection end map until the timing mark lines up.

306884

Kept notes on Transfers Closing, Inlet Opening, Inlet Closing and BDC. So now I am confident that I can accurately position the injection end time.

Ran the bike up on the dyno, started Ok and ran fairly well pulling 11k+, runs well up to 9k'ish but still has the deto problem over 10k. So will put a little bit of time into seeing if we can tune that out. If that does not work then I guess injecting into the transfers will never work and I will move the main injector to the inlet tract and see how that goes.

Its the last roll of the Dice and if I don't get any joy there then this EFI thing is destined for a Turbo 4T CVT project.

[wobbly]

Reed petals natural vibration frequency ( rpm ) can be determined easy enough in EngMod, but when adding backup stiffeners
especially with rev plates it all gets way too complex way too quickly.
Using reeds that are too thin shows up in the sim as the tip lift going spastic on successive iterations, one run the reed will open all the way and hit
the stops.
The next run it will open early but nowhere near all the way.
Due to this the inlet wave goes mental as well, and power drops.
On the dyno the thin reed will make good mid power then loose it all up top.
But using a rev plate and a backup stiffener you can use a reed that is in effect too soft but control the errant lift profile.
I have always used 0.4 or 0.5mm rev plates, and have found that for some reason,thick fibreglass backups seem to make more power as well.
The 0.5mm spacing lets the a thin reed open quickly, but the backup then takes over and damps the uncontrolled oscillations and excess tip lift.
The only way to test any of this is to dyno combinations of thickness, and varying backup length.
I have used very this 0.25 carbon main petals, but they require long and thick backups, and ultimately slightly thicker ones have worked better.
But that was with the specific engine I was testing on,they all respond differently.
Great thing about the revplate and backup idea is that you can also change the stiffness on top and bottom for intakes that are bent down due to the carb bowl angle.
But also you can vary the backup length across the reed block, to bias the flow back toward the inner petals in an engine that has the manifold bent to the side - like most MX setups.

[seattle smitty]

while im thinking of it, whats everyones preference for texture on the walls ? ive heard alot of various opinion on this subject, mostly from noobs that dont know much, so i figured i would ask the experts here. ive always just used the carbides and pretty much left that texture on the walls but maybe theres something better ?

I'd like to hear some educated answers on this, too. My "swag" (scientific wild-ass guess) on this is that the long-side turn and the sides of the transfers (and also the whole inside surface of the crankcase) ought to have a textured surface similar to what gets left by glass-bead blasting. However, since glass-bead is very dangerous to the engine since it sticks in every crevice and embeds itself in cast aluminum, another media, say salt, would be safer. The inside turn or short-turn of the transfers should have the textured surface, but golfballed with small dimples. How you accomplish this in cylinders without sleeves (and many that have sleeves) is, um, an interesting challenge. And of course this is only a guess. AND, you first have the shapes and sizing of the transfer passages, and the aiming and timing of the port-entries into the cylinder just right to begin with, making any worries about the surface treatment secondary or thirdendary. But again, this is all rank (very rank) speculation, presented in hopes that the smart guys will provide the straight dope here.

[Martin1981]

thank you for the detailed answer, wob. as usual very interesting.

so i will make carbon reeds with 0,3mm thickness. the spacer with 0,5mm and backups with 0,4mm (you said that 0,5mm backups are too thick.) but probably one can not totally nail it down to one perfect setup for all engines.

by the way, sweapatrick tried the setup you posted and said that in comparison to that the vforce 2 can stay home. do you think that this custom made reed setup can even be better than the vforce 2?


you mentioned the bend intake on mx engines. indeed, i am working on a 1986 CR 125. either i make a dead straight intake or i will have the bend between reedcage and intakeport to fight the flow issues. but i think even with the bend not between the reeds and the carb, there maybe problems. so the best way should be a straight intake without any bends.

[Drew]

[SIZE=3]
Its the last roll of the Dice and if I don't get any joy there then this EFI thing is destined for a Turbo 4T CVT project.
That would be a terrible shame, but I think no one would begrudge the decision.

From what little I've retained reading these pages, det can be managed by backing timing off and feeding in a shit tonne of fuel.

Is there a field in the map that's not doing much at the moment, you could set to open an injector over certain rpm and just leave the bastard squirting straight through the transfer port at the piston top to cool it when it's down?

Or have I not grasped the basics again?

[wobbly]

The CR125 will make around 2Hp with a dead straight intake, over the best bent one.
An old RS125 short manifold one if you are reving to 13.000 or the longer late model RS125 one if you need more mid power.
The VF2 works very well in a CR125/RS125 and I have not been able to get a stock cage of any sort to make as much power.

[peewee]

you mentioned the bend intake on mx engines. indeed, i am working on a 1986 CR 125. either i make a dead straight intake or i will have the bend between reedcage and intakeport to fight the flow issues. but i think even with the bend not between the reeds and the carb, there maybe problems. so the best way should be a straight intake without any bends.


or you could do what ktm did, although it may be alot of work

both cylinders have the same total angle of 20*. the honda on the left has the full 20* in the manifold which makes a kink so to speak. ktm on the right has 10* angle in the cylinder inlet and the other 10* in the manifold. who ever said them guys at ktm were a bunch of rubes :bleh:

[husaberg]

thank you for the detailed answer, wob. as usual very interesting.

so i will make carbon reeds with 0,3mm thickness. the spacer with 0,5mm and backups with 0,4mm (you said that 0,5mm backups are too thick.) but probably one can not totally nail it down to one perfect setup for all engines.

by the way, sweapatrick tried the setup you posted and said that in comparison to that the vforce 2 can stay home. do you think that this custom made reed setup can even be better than the vforce 2?


you mentioned the bend intake on mx engines. indeed, i am working on a 1986 CR 125. either i make a dead straight intake or i will have the bend between reedcage and intakeport to fight the flow issues. but i think even with the bend not between the reeds and the carb, there maybe problems. so the best way should be a straight intake without any bends.


or you could do what ktm did, although it may be alot of work

both cylinders have the same total angle of 20*. the honda on the left has the full 20* in the manifold which makes a kink so to speak. ktm on the right has 10* angle in the cylinder inlet and the other 10* in the manifold. who ever said them guys at ktm were a bunch of rubes :bleh:
This is the intake Wob refered to.
http://www.swedetechracing.com/parts_accessories/rs125-intake_pre-95.html
306904306905

They also do these
306906306907
http://www.swedetechracing.com/parts_accessories/cr125-intake-reed-cage.html

[wobbly]

No husaberg the old RS125 one is very short and dead straight.
The KTM does reduce the asymmetric flow within in the reedblock, but then that reduced asymmetry is made alot worse by having
the flow exiting the reed tips made to run off to one side of the cylinder/case,no matter what is happening within the reed.
This will mean that no matter how clever the reed tensions are made to equalise the flow exiting the tips,the flow into the transfer duct entries
above the crank will always be asymmetric.
Not so clever at all IMHO.
As I said in a CR125 or a RS125 having the dead straight manifold is worth a couple of HP, as the flow is dead straight horizontally as well as vertically.
In the KTM that is actually impossible.

[husaberg]

No husaberg the old RS125 one is very short and dead straight.
The KTM does reduce the asymmetric flow within in the reedblock, but then that reduced asymmetry is made alot worse by having
the flow exiting the reed tips made to run off to one side of the cylinder/case,no matter what is happening within the reed.
This will mean that no matter how clever the reed tensions are made to equalise the flow exiting the tips,the flow into the transfer duct entries
above the crank will always be asymmetric.
Not so clever at all IMHO.
As I said in a CR125 or a RS125 having the dead straight manifold is worth a couple of HP, as the flow is dead straight horizontally as well as vertically.
In the KTM that is actually impossible.

Really this is the part number they refer to in the pic?
P/N 16220-NF4-900)

So you mean the one on the Left with a post 95 (NX4) part code?
16210-NX4-000
looking at the bottom
27mm plate to carb both sides
http://www.risingsuncycles.com/images/Honda_parts/carb_isolators.htm
http://www.risingsuncycles.com/images/carb-parts/botmveiw.jpg

[wobbly]

Yep, thats the trick shit part for the last of the MX based RS125s - NLA,except a few lying around that were used in open class CR125 engines before they stopped them in USA.
Thats worth a couple of Hp and then stick on a short PWM or better SPJ and thats another 1 1/2 at the top ( over PWK ) in the MX or early RS125.

[peewee]

No husaberg the old RS125 one is very short and dead straight.
The KTM does reduce the asymmetric flow within in the reedblock, but then that reduced asymmetry is made alot worse by having
the flow exiting the reed tips made to run off to one side of the cylinder/case,no matter what is happening within the reed.
This will mean that no matter how clever the reed tensions are made to equalise the flow exiting the tips,the flow into the transfer duct entries
above the crank will always be asymmetric.
Not so clever at all IMHO.
As I said in a CR125 or a RS125 having the dead straight manifold is worth a couple of HP, as the flow is dead straight horizontally as well as vertically.
In the KTM that is actually impossible.

straight inlet and kinked manifold or rotated inlet and slightly less kinked manifold. either way you look at it i guess youll have more mixture piling up on one side of the inlet as it tries to turn the corner.

well i got started cutting the aux. everyone talks about the axial angle on A,B and C but never any mention of the axial for the roof and floor of the aux. got any suggestions ? tried to look at the rsa but couldnt really tell much from the odd angle photos ive seen

[husaberg]

straight inlet and kinked manifold or rotated inlet and slightly less kinked manifold. either way you look at it i guess youll have more mixture piling up on one side of the inlet as it tries to turn the corner.

well i got started cutting the aux. everyone talks about the axial angle on A,B and C but never any mention of the axial for the roof and floor of the aux. got any suggestions ? tried to look at the rsa but couldnt really tell much from the odd angle photos ive seen

Have a look in the Rsw Drawings........

[peewee]

yes i should of thought of that. it appears the floors angle down immediatly from the bore edge. the roof however looks to be flat for a few mm into the duct and then angle downward. do you agree ?

[husaberg]

yes i should of thought of that. it appears the floors angle down immediatly from the bore edge. the roof however looks to be flat for a few mm into the duct and then angle downward. do you agree ?

that tallies with the DEA cylinder I have seen
plus this cad rendering of the RSW one
http://www.kiwibiker.co.nz/forums/album.php?albumid=4839&attachmentid=301360
Mr Payart has posted quite a few pics on his pitlane thread inc 3d pics


Here.
Let's hear it for Mental Trousers: he created a way for me to upload BIG files.
I will be offline for a couple of days, but this might keep you busy:

http://www.kiwibiker.co.nz/manual/Aprilia-1.zip
http://www.kiwibiker.co.nz/manual/Aprilia-2.zip
http://www.kiwibiker.co.nz/manual/Aprilia-3.zip
http://www.kiwibiker.co.nz/manual/Aprilia-4.zip
http://www.kiwibiker.co.nz/manual/Aprilia-5.zip

One request:
Don't spread the contents all over the world wide web.
Then I might upload some collected data of other racing brands as well.

Enjoy.

[peewee]

i think what ill do is just make the port as big as need be. then weld a bubble over the outside so theres still water circulation

[F5 Dave]

And then test it for leaks. Water inlet in the back - nice. Is that a later CPI like a Wampus or something?

[husaberg]

Other pics




Attachments Posted by husaberg
Attachment Statistics
You are currently using 1.24 GB to store 7,139 uploaded attachments.:innocent:

[TZ350]

306944 Pumper

With a pumper carb this engine reliably made 28hp at 12,250 rpm, with EFI, 24hp at 11,500rpm is the best so far and the EFI is short about 1,000 rpm.

306943 EFI

Fuel pump packed up so gave up for the night. Ok this is where I am at, pretty much the same position as 6 months ago. Still detos like crazy especially on over run so I will try Drews idea and run a 3D ignition map that backs out a lot of ignition particularly on part throttle. And play a little with the injection end point. I will give it a few nights then try the direct injection down the inlet idea.

[speedpro]

I thought the problem was "auto" ignition caused by the mixture in the transfer ducts being heated by a burst of hot exhaust gas overcoming the weak pressure in the case/duct momentarily before it finally makes it's way into the cylinder where it is polluted by burnt hot gases before being compressed at which point it autoignites. Supposedly more of a problem with methanol as methanol is more prone to autoignition when mixed with combustion products.
If that is the case, if, pissing with timing is not going to make any difference as it is not a regular ignition event causing the problem. Playing with the mixture may help but will cause problems with pipe temp affecting throttle response.

maybe.

[Martin1981]

or you could do what ktm did, although it may be alot of work

both cylinders have the same total angle of 20*. the honda on the left has the full 20* in the manifold which makes a kink so to speak. ktm on the right has 10* angle in the cylinder inlet and the other 10* in the manifold. who ever said them guys at ktm were a bunch of rubes :bleh:


that`s what i was think of peewee. but like wob said. even having this work done you still have a bend. so i will go for dead straight probably. the only thing i need then is a trick shit rubber boot to connect the carb to the airbox.

[husaberg]

Yep, thats the trick shit part for the last of the MX based RS125s - NLA,except a few lying around that were used in open class CR125 engines before they stopped them in USA.
Thats worth a couple of Hp and then stick on a short PWM or better SPJ and thats another 1 1/2 at the top ( over PWK ) in the MX or early RS125.

When you run out of those have a look at these big enough base plate to be modified to fit any number of bikes only 35mm carb though :)

[TZ350]

I thought the problem was "auto" ignition caused by the mixture in the transfer ducts being heated by a burst of hot exhaust gas overcoming the weak pressure in the case/duct momentarily before it finally makes it's way into the cylinder where it is polluted by burnt hot gases before being compressed at which point it autoignites.

Detonation was not a problem with the carb and 3D ignition map until well past 12K rpm.

But .. Yes Auto ignition and I think you are right about the EFI creating a weak mixture in the transfers so I intend putting in some effort to get the timing of the injection squirt to coincide properly with the transfer port open time.

When I shut the EFI beast off at 9-11.5K rpm the deto sounds like a swarm of very angry bees.

[41juergen]

Hi everybody, my name is Juergen, I'm from Frankfurt (Rhein-Main Area) in Germany.
I found this fantastic thread some month ago and it took me some time to get through it. Of course it's the most valuable source in the net, thanks’ to TZ, Wob, Frits and all the others sharing your knowledge. As per good advice I got the EngMod software paid by my wife (with the basic idea better to simu some pistons to dead rather than buying new ones... :msn-wink:).

So I use a RZ PV engine with a 66x58mm setup, STA's to reach approx. 50 HP per cylinder, a 0,8mm squish with 48% SAR, 38mm Mikunis, a zeeltronic and a "tuned" pipe setup. Now playing with the numbers some questions raised up:
- for the scavenging model I use Yam1 for the modified ports setup. Is that ok?
- is a combustion efficiency value of 0,9 too high for that setup? I get detos at approx. 8000 rpm by using 100 octane fuel and can get rid only by going down with AFR to 11.2...
- is a TL for the pipe of 950mm too long for max. power at 10500 rpm and 130 tr and 200 ex timing? The power / torque curve shape looks not too bad with having max power at 11.000 rpm but than going down fast (even with playing with the ignition and AFR)...

Thanks’ for any help...
Juergen

[Muciek]

Detonation was not a problem with the carb and 3D ignition map until well past 12K rpm.

But .. Yes Auto ignition and I think you are right about the EFI creating a weak mixture in the transfers so I intend putting in some effort to get the timing of the injection squirt to coincide properly with the transfer port open time.

When I shut the EFI beast off at 9-11.5K rpm the deto sounds like a swarm of very angry bees.

Here are BRC EFI 125 engine videos

https://www.youtube.com/watch?v=8AWlJN4QMws



https://www.youtube.com/watch?v=Kfx61bUOznc

And photos of power curve and inlet
306947306948

Using ball valve slide injectors can be in front of it or they should be behind it?

[TZ350]

Two injectors in the inlet, guess where we are going shortly, thanks for the pictures.

[TZ350]

Hi everybody, my name is Juergen, I'm from Frankfurt (Rhein-Main Area) in Germany.

Hi Juergen, welcome.

[Frits Overmars]

everyone talks about the axial angle on A,B and C but never any mention of the axial for the roof and floor of the aux. got any suggestions ? tried to look at the rsa but couldnt really tell much from the odd angle photos ive seenThe roof axial angle should be about 20° down; the floor could use a bit more downward angle, but that would land you in the A-transfers, so you'll have to becareful there.
The radial position angle of the RSA's aux. exhaust ducts is quite radical; past mid-cylinder. But the radial direction angle is less severe.
The drawing below shows that the flanks of the aux ducts start with 20° less than the radial position angle, irrespective of the radial position angle that you may choose. And don't overdo it or you might get massive short-circuiting from the A-ports to the exhausts, even when using RSA-type closed-end piston pins.

[Frits Overmars]

As per good advice I got the EngMod software paid by my wife (with the basic idea better to simu some pistons to dead rather than buying new ones).Hallo Jürgen, herzlich willkommen. That certainly was a good advice. Now I could use some advice from you: where can I find a wife like yours? Has she got any sisters?
is a TL for the pipe of 950mm too long for max. power at 10500 rpm and 130 tr and 200 ex timing? The power / torque curve shape looks not too bad with having max power at 11.000 rpm but than going down fast (even with playing with the ignition and AFR).The tuned length is in the neighbourhood; maybe a bit on the long side. Long pipes will force you to run a late ignition timing and/or a lean mixture if you insist on reaching a certain rpm level. But I suspect that the main reason for the power collapse after 11.000 rpm maybe the blowdown time.area. Short-stroke engines tend to suffer more than average in this respect.

[wobbly]

950 pipe will work fine, but if you are getting deto then the Comb eff is too high ( around .85 to .88 in big bore RZ ) the stinger is too small
or too much ign timing.
12:1 AFR is normal, and you can only change this if you are using a solenoid powerjet over the top.
130 transfers is very high - I would be looking to increase the width and reduce the height, plus make Aux Ex port top edge as big as possible
+ 72% width at the top of the main.
As Frits says the big power drop is likely blowdown related, do you have a big rise in pressure in the transfers as they open.
Here is RZ400 dyno curve for road racing with 955 pipe

[speedpro]

.. Yes Auto ignition and I think you are right about the EFI creating a weak mixture in the transfers.

Auto ignition - yes, weak mixture - no.

The problem as I understand it is that because the throttle is closed there is hardly any crankcase compression. As the transfers crack open, even though there was not a lot happening on the previous power stroke and not much exhaust to be spent, because of the minimal crankcase pressure there is an amount of exhaust blown down the transfers. This mixes with the fresh charge. Eventually this mix of old & new makes it's way into the cylinder where it doesn't do a particularly good job of scavenging the cylinder, is trapped as the ports close and then compressed. This mixture of combustion products from the previous cycle and fresh mixture is prone to auto-ignition, which as I said is worse for methanol. I don't know exactly why but guess it's due to the chemical composition of the gases and a bit of heat.

Changing the ignition timing has no effect as it isn't the ignition spark that ignites the mixture. Changing the fuel ratio "might" have an effect but as the unburnt gases from the previous cycle remain in the cylinder so will the problem remain.

I think Frits suggested somehow lowering the transfers and therefore blowdown which could have a positive effect.

Didn't Honda deliberately use this characteristic in a 250cc Paris-Dakar type bike?

[Drew]

What Speedpro is saying makes sense, but lowering the piston crown temperature (by running rich and backing off timing) reduces det (pre ignition in old speak?) I thought.

Oh yeah, please read all my posts as questions rather than facts. I am perpetually ignorant and have a mongrel habit of blending several pieces of unrelated info together.

[wobbly]

Do some study - Deto and PreIgnition are completely unrelated phenomenons.

[speedpro]

Detonation as I understand it - The regular ignition event starts the process of combustion. This process is not instantaneous but involves a flame front burning it's way through the mixture. As this happens heat is created which raises cylinder pressure. This heat is radiated to the remaining unburnt mixture which is also heated by the rising cylinder pressure. Detonation is the event that happens when the rising heat and pressure from the advancing flame front gets to the point where the so-far unburnt mixture attains a state where it ignites spontaneously rather than as part of the flame propagation of normal combustion.
Reducing temperatures will of course reduce this tendency as will concentrating the mixture to be burnt in a smaller space and also increasing the flame propagation rate, typically for our motors by keeping the squish tight which concentrates the mixture and also creates turbulence by squishing(get it? - squishing) the mixture in the squish band area into the chamber at something like 30m/s. The small amount of mixture remaining in the squish area is cooled by the very close proximity of the piston and head and therefore is less prone to detonation, or even combustion which does not help emissions.

Preignition is exactly what the word implies. Prior to the regular ignition event there is something that starts ignition prematurely. Typically I'd imagine something like a hot valve or bit of carbon or possibly an overheated spark plug.

[husaberg]

Do some study - Deto .

Didn't Mr Thiel eliminate a lot of the Deto issues with the Aprilia by making the head casting waterways thinner there're by exposing them to better coolant flow.
Maybe TZ350 head doesn't have enough water flow:rolleyes:
Seriously though, Rob what are you using to monitor you fuel mixture.
Someone brought up a few pages back that aircoolled two strokes are petrol cooled.

[peewee]

And then test it for leaks. Water inlet in the back - nice. Is that a later CPI like a Wampus or something?

no its one of them cp honda cylinders. cant recall the name. just used it for illistration puposes to show the bubble around the aux tunell