ESE's works engine tuner

[andreas]

There used to be stronger springs available for the 350 ypvs, possibly they will fit, the xt 600 has 5 springs as yours does.

[Muciek]

But 44hp isn't stock power or close to it?

[F5 Dave]

Actually yeah. 45 should be stock 1KT.

Might have to shell out for some new genuine Yam plates.

The old RZ ones had these silly rubber rings but FZR plates were wider, as in smaller OD so more area where rings used to be.

[Muhr]

makes sense. the transient response of the pipes is very similar as you can see in the inclination of the logged temps, I would have expected the thinner one would react faster. likely the 1 mm variant contains more energy due to the higher thermal mass, which adds energy to the exhaust gas off throttle. transient behavior is always hard to judge up front.

It's important to use the same thicknesses of thermo couples for both tests, a thinner one will react faster and lead to wrong conclusions.

Side note - I do car manifolds/exhausts for a living at a Tier 1 supplier, and have some inside about material choice/properties/behavior. Personally I'd stay away from Inconel, it's only necessary for really high temp applications like supercar manifolds to maintain some sort of strength on full load. If the welding process and penetration are not absolutely perfect you get all kind of funny failures (cold cracks, hardened weld seams,...). Just use some 1.4301, very similar thermal properties and fraction of the price.

Hi we have now done more tests even with 4301 1mm (which unfortunately was prone to cracking) what we ended up with which I consider superior in terms of the smallest possible drop in exhaust temperature is inconel or rather as thin a sheet as possible in this case 0,5mm inconel. image below from the latest test with inconel, with adjusted length for the increased average temperature and conservative jetting. Hope to be able to do some test with titanium in the future

[jfn2]

Katinas:
I was telling a friend of mine about your thinking on rounding the timing edge that we talked about some time ago, so I took his engine apart to rering it and looked what I found.
This is a YZ125 piston made by wiseco. I didn't measure it yet but it looks like 3-4 mm. It goes the whole way around the piston edge. It does not stop at the c-port area. The head does not reflect the radius of the piston. I will have to try that later on. I don't think they would have taken the time for this rounding if it didn't produce some kind of advantage, but then this is not a cheap piston either.

[SwePatrick]

But 44hp isn't stock power or close to it?

Mine is far from stock ;)

[SwePatrick]

I´ll try this first before start throwing new parts at it(and maybe all wasted)

I have added 4 springs:

[TZ350]

.

I have added 4 springs:

https://forumbilder.com/images/2020/09/02/clutch1.jpg
https://forumbilder.com/images/2020/09/02/clutch2.jpg

That is very clever. I wish I had thought of it when I needed to beef up my own clutch.

[Brett S]

Katinas:
I was telling a friend of mine about your thinking on rounding the timing edge that we talked about some time ago, so I took his engine apart to rering it and looked what I found.
This is a YZ125 piston made by wiseco. I didn't measure it yet but it looks like 3-4 mm. It goes the whole way around the piston edge. It does not stop at the c-port area. The head does not reflect the radius of the piston. I will have to try that later on. I don't think they would have taken the time for this rounding if it didn't produce some kind of advantage, but then this is not a cheap piston either.


That first picture looks like the drilling for the anti rotation pin has hit the bottom ring land?

[Frits Overmars]

I´ll try this first before start throwing new parts at it(and maybe all wasted). I have added 4 springs:That is quite a clever solution Patrick. But didn't the required manual force become very high?
You might try this oil; it was developed by Addinol in collaboration with Langtuning (www.langtuning.de (http://www.langtuning.de)) precisely for your kind of problems, with remarkable results (and no, I do not get a percentage :D).
347099

[andreas]

How is the load from the new springs applied to the hub?

[SwePatrick]

That is quite a clever solution Patrick. But didn't the required manual force become very high?
You might try this oil; it was developed by Addinol in collaboration with Langtuning (www.langtuning.de (http://www.langtuning.de)) precisely for your kind of problems, with remarkable results (and no, I do not get a percentage :D).
347099

Thanks :)

It actually didn´t raise the force needed in hand that very much, i though if it happened i´ll make it hydraulic also ;)

Thanks for the link of the oil, it might be needed :niceone:

It did a fast test today, no full pull in dyno as it was late in the evening, it seems promising, now the tire broke loose instead.

[SwePatrick]

How is the load from the new springs applied to the hub?

The spring are 'seated' in 'cups', the cups locks in the pressureplate, then is tightened against the new stainless disk.

[SwePatrick]

.


That is very clever. I wish I had thought of it when I needed to beef up my own clutch.

Nice, thanks =)

I always work with this tale cirkulating in my head: 'If mohammed won´t go to the mountain, then the mountain has to come to mohammed'

[andreas]

The spring are 'seated' in 'cups', the cups locks in the pressureplate, then is tightened against the new stainless disk.

Ok, in my mind that does effectively nothing to raise the pressure on the plates?? Meaning it's just a compressed spring doing no work unless it is also anchored to the hub.

[SwePatrick]

You need to think again ;)

The stainless disc is the 'wall' the springs rests at, both oem and the added, this is locked to the hub with the four countersinked screws..
Then there are cups that are oem and added cups that holds the springs.

The same function as oem, just no screws inside them, almost like zundapp´s clutch, just the other way around.

https://www.google.com/search?q=clutch+spring+cups&client=firefox-b-d&sxsrf=ALeKk02RqpV2ylrGUfISwErRQvHVs6q5TA:159907763 9029&source=lnms&tbm=isch&sa=X&ved=2ahUKEwi52ZG1pMvrAhX2BRAIHULQDJEQ_AUoAXoECAsQA w&biw=1440&bih=754

[andreas]

I was thinking again, and you have a gap between the pressure plate and your new plate. I like it.

[katinas]

Katinas:
I was telling a friend of mine about your thinking on rounding the timing edge that we talked about some time ago, so I took his engine apart to rering it and looked what I found.
This is a YZ125 piston made by wiseco. I didn't measure it yet but it looks like 3-4 mm. It goes the whole way around the piston edge. It does not stop at the c-port area. The head does not reflect the radius of the piston. I will have to try that later on. I don't think they would have taken the time for this rounding if it didn't produce some kind of advantage, but then this is not a cheap piston either.

Hi jfn2

Such radius with unmatched head may cause detonation if the other settings (ignition, compression, squish height and width) are selected correctly.

It is not difficult task to change head shape, for rounded crown piston without sharp part at C. But some playing with ignition timing will be needed. Maybe slightly retard.

[SwePatrick]

Made a couple of pulls today, this is the best one.
White line is dyno roller, Yellow is engine rpm, they should follow eachother.

Clutch managed to transfer 37.21Nm while slipping.
Weather was really moisture today, almost 74%
I also pulled a couple of degrees ignition from it today, wanted to run safe while searching for problems with the clutch, this to also make the torque to come in smoother.

[jfn2]

Brett S:
Yes, if you look at the pics you'll see the ring pin was installed horizontally and the pin dia is slightly larger than the ring land.

Katinas:
If you look at these new pics you'll see I have no detno, in fact I think I'm a little rich, and the timing is stock. Although right off hand I don't know what that is. But I will be keeping an eye on it in the future. I would have to look but I think my squish is .85mm. And yes I know that my exhaust port bridge is not quite recessed enough. Since I can not do anything about the rounding on this piston it will have to do and I will work on the head rounding. I will leave you know what I come up with.

[ken seeber]

jfn2,
It looks to me like the anti rotation pin hole is on centre with the ring groove. This means that there is a leakage path around the back of the ring and outwards underneath the ring. Bad.:nono:

The drilling and pin should always be above the bottom of the ring groove. See pic. The small darkness under the pin is just a reflection of the pin.

347117

[wobbly]

Yes , the ring pin from Wiseco has a leakage path on the ring land bottom seal face - dumb.
Now I must admit I never understood the need to have engine rpm on the Y scale , makes perfect sense when you compare the dead straight roller speed delta to the engine rpm to see any slip.
But there is also the possibility to plot slip % as a calculated chanel , but shit , never needed normaly as you can hear a slipping clutch immediately.

The other thing that i found with radiused piston timing edges is that the rule of thumb is to drop the cylinder by 1/2 the radius ie 1mm rad = 0.5 drop.
Then the advantage of the radius alone is seen on the dyno - a good increase all the way up the front side power , but a drop in overev.
But going the extra mile of hard work and stopping the radius each side of the boost port , and power increases everywhere.
Of course the head has to be radiused as well , or the base deto level increases dramatically. - thus lowering the available leeway when tuning to the edge.

[SwePatrick]

Now I must admit I never understood the need to have engine rpm on the Y scale , makes perfect sense when you compare the dead straight roller speed delta to the engine rpm to see any slip.
But there is also the possibility to plot slip % as a calculated chanel , but shit , never needed normaly as you can hear a slipping clutch immediately.



It´s hard to hear exactly where it starts to slip, but easy to hear when it´s out of control.

[Frits Overmars]

I must admit I never understood the need to have engine rpm on the Y scale , makes perfect sense when you compare the dead straight roller speed delta to the engine rpm to see any slip. But there is also the possibility to plot slip % as a calculated chanel , but shit , never needed normaly as you can hear a slipping clutch immediately.
It´s hard to hear exactly where it starts to slip, but easy to hear when it´s out of control.Agreed. You can easily play it by ear if engine rpm suddenly starts rising at twice the rate. But clutches have more tricks up their sleeves, like creeping; say during 30° of each crankshaft revolution, i.e. about 10° per clutch revolution. That is not so obvious to the ear, but it would mean a 8% power loss. Which would heat the clutch, which.... etc. Power can sometimes be found by working on a clutch that didn't audibly slip.

[F5 Dave]

I have had that scenario. I'd increased the plate area but accidentally decreased the spring tension not noticing different models had different springs from my stash.

It acted as a power regulator. Wouldn't get past a certain power level.

[SwePatrick]

I found the slip calculation function in the software.
question is, how to use it?
Or more correctly use the percentnumbers to use, let´s say lost power calculations?

[wobbly]

I have only just loaded V40 and have never needed to use "slip % " . But its available as an automatic calculation under Test menu .
All that gives you is a % difference between the engine speed delta Vs roller speed delta that would always be 0 % with no slip , either from a tyre on a roller , or a clutch allowing the previously set gear ratio to change.

[SwePatrick]

I have only just loaded V40 and have never needed to use "slip % " . But its available as an automatic calculation under Test menu .
All that gives you is a % difference between the engine speed delta Vs roller speed delta that would always be 0 % with no slip , either from a tyre on a roller , or a clutch allowing the previously set gear ratio to change.

I´ve got this insanly high slip percentage, like 280%
I dunno what to do with the number, it only tells me it slips a lot.

Is it 280% higher engine rpm than it should be with no slip?

[F5 Dave]

Surely at beyond 100% slip you into negative slip. You could just be on to something if you can harness that. :clap:

[adegnes]

Surely at beyond 100% slip you into negative slip. You could just be on to something if you can harness that. :clap:

Infinite Improbability Drive

[Flettner]

Infinite Improbability Drive

So Adegnes, you return with a report.
The 'pegged' ring works, yes we have been watching. Anything else of intetest to report to wet our appetite.
A jolly good old 'well done' is in order.

[adegnes]

So Adegnes, you return with a report.
The 'pegged' ring works, yes we have been watching. Anything else of intetest to report to wet our appetite.
A jolly good old 'well done' is in order.

Thanks! At work atm, I'll be back with the report.

[F5 Dave]

I'll put the kettle on.



(For a really hot cup of tea).

[wobbly]

My guess would be that the slip % represents the calculated difference between the engine acceleration rate vs that of the roller.
if the inputted overall gear ratio between the two is exceeded by x 2.8 then you have 280% slip.
Exactly like doing a run in 1st gear , instead of 6th , without changing the set ratio previously calculated from the rpm histogram..

[Frits Overmars]

I´ve got this insanly high slip percentage, like 280%
Surely at beyond 100% slip you into negative slip.
My guess would be that the slip % represents the calculated difference between the engine acceleration rate vs that of the roller.
if the inputted overall gear ratio between the two is exceeded by x 2.8 then you have 280% slip.
Exactly like doing a run in 1st gear , instead of 6th , without changing the set ratio previously calculated from the rpm histogram..I'm with Wobbly. I'd leave the acceleration rate out of the equasion but I'd say that 100% slip means that the crankshaft turns twice as fast as it should, given the transmission ratio.
So, if the calculated riding velocity with a given crankshaft rpm is 380 kmh, and the real speed is only 100 kmh, you have 280% slip. It may not be negative, but in any case it is insanely high.

[SwePatrick]

I´m having some issues taming this engine, but it´s just keep on trying new things.
I noticed Yamaha YZ250F 2001-11 clutchdiscs might work, they´re just a couple of tenth´s bigger in outer diam, same width on the tabs, and same innerdiameter.
Rekluse seem to have thinner discs, and by that i can fit more discs.
YZ125 91-92 might also have the same dimensions.

Can anyone confirm these measurements on those?(in picture)

And then one more question, if running extremely rich, is it possible it starts to bang in the pipes on wide open throttle when making a dynopull?
I noticed the engine is somewhat difficult to jet as i cant make any serious pulls in dyno when the clutch slips.

347157

[Frits Overmars]

if running extremely rich, is it possible it starts to bang in the pipes on wide open throttle when making a dynopull?
I noticed the engine is somewhat difficult to jet as i cant make any serious pulls in dyno when the clutch slips.That would require unburnt mixture in the pipes and an ignition source. The first requirement can be met with a mixture that is so rich it won't ignite, and the second requirement with a mixture that is so rich that it will ignite, but burn so slowly that combustion is still going on when the exhaust ports open. By the way, an overly-lean mixture could show a similar behaviour.

[SwePatrick]

That would require unburnt mixture in the pipes and an ignition source. The first requirement can be met with a mixture that is so rich it won't ignite, and the second requirement with a mixture that is so rich that it will ignite, but burn so slowly that combustion is still going on when the exhaust ports open. By the way, an overly-lean mixture could show a similar behaviour.

More info that might help you distancediagnose:

When cold, just after i shut off the choke´s it is running really nice, no pops and bangs.
But after just a couple of freerevving blips on the throttle, say, five to six times it starts to pop when engine is decelerating(closed throttle)

I figure when freerevving it doesn´t burn the fuel fully and it build up in the pipe, and finally pops and bangs.
Then it all continues and getting worse the warmer the engine gets, to me it says rich mixture.

I´m having a hard time reading the plugs as the runs in dyno becomes so short when it slips.

[jfn2]

SwePatrick:
I just measured a 2004 YZ125 clutch plate and it has the same dimensions as one you posted.

[wobbly]

For sure sounds rich if it gets worse as it warms up.
The overly rich mixture is burning so slowly , as the piston is descending , that its still happening when the Exhaust port opens.
One way to see if its very rich oround idle ( closed throttle ) would be to start it with no choke at all.
If it runs fine with no choke , then thats the story right there.
If its lean down low then it wil take ages to settle down to an idle , that also can have a mixture so lean it burns slowly and pops when backing off.
But again , that can be tested by leaving the choke on , if the pops go away , even if idle is OK , then that is the other story being told.

[andreas]

Maybe it's the story of a wasted spark setup.

[SwePatrick]

SwePatrick:
I just measured a 2004 YZ125 clutch plate and it has the same dimensions as one you posted.

Nice,, thank you.
this will make things easy, i can fit two or three more plates with the rekluse ones, dunno thickness of them yet, but from what i can see on pictures.

[SwePatrick]

Maybe it's the story of a wasted spark setup.

Might be, but i´ll test everything else first as i know many many twostrokes run the same setup.

[SwePatrick]

For sure sounds rich if it gets worse as it warms up.
The overly rich mixture is burning so slowly , as the piston is descending , that its still happening when the Exhaust port opens.
One way to see if its very rich oround idle ( closed throttle ) would be to start it with no choke at all.
If it runs fine with no choke , then thats the story right there.
If its lean down low then it wil take ages to settle down to an idle , that also can have a mixture so lean it burns slowly and pops when backing off.
But again , that can be tested by leaving the choke on , if the pops go away , even if idle is OK , then that is the other story being told.


Yes, the first symptom sound accurate, i´ll make some test this evening.
It´s mind distubing that the plugs says go the other way, but i guess i can't read the plugs as the pulls in dyno is so short, just a couple of seconds as the clutch slips.
I actually think it´s the powerjets that are messing with me.(i´ll block them off first)

I need to fix the clutch, and might have a solution with the yz250f discs.

[F5 Dave]

Might be, but i´ll test everything else first as i know many many twostrokes run the same setup.

Methanol with wasted spark will ignite. Petrol unlikely

[Frits Overmars]

It´s mind distubing that the plugs says go the other way...You are using methanol fuel, aren't you Patrick? My limited experience with methanol taught me that you must not try to get the plugs dry. The engine will perish before the plugs dry up.

[adegnes]

So.
After half a year of brain cooling axe-work I'm back at it.
If you've watched the videos you know that I've managed to start the engine on the primary intake, and that's about it.

Short description of the specimen in question:

347170

- 50cc
- Primary reed intake, secondary valveless intake
- Primary = carb on gas, secondary = continous nitromethanol injection
- 100% bore width exhaust port
- special piston(thanks makr) with retained ring
- CVT transmission, electronically controlled belt tension.

So far(admittedly not very far) the ring has not snagged, not with it's original full "T" profile, nor after grinding away everything but two short tabs opposite of the ring gap.

Ring with full "T".
347174


Two small tabs left.
347173

With the full "T" I struggled with getting it to seal properly, uneven pressure, tight in some areas, not even touching the bore in some. No quite sure what made it behave like this. Twisting force?
With tabs the ring seems to be sealing fine, and in the middle of the exhaust port is really the only place it needs to be retained.
A better solution, provided it stays in one piece...
Mark has a thinner (0.5mm) ring and corresponding piston planned/in the making, the current ring (1mm) is too soft, and probably to heavy for higher rpm.


347167
347168
347169

Massive case volume(390cc), hard to say exactly where the intake ends and the case begins - effective case volume might be smaller.

Hard starting, probably due to primary compression being far from reed friendly. Last test was with 50cc of crank stuffing, but prior to that a backfire cracked my reeds(sanded from 0.4 to 0.2mm),and the test was performed with a different reed cage. Ran much better.
Next test without the stuffer, hoping it was the reeds that helped.

Must admit I didn't give the primary much thought while designing the engine, should have...

As long as it's possible to start, warm up, and pull into the powerband I'm happy, after that the secondary intake takes over.

That PVC plumbing valve is a placeholder for a more refined thing, will be run fully open/closed.
347175


In retrospect I regret not designing in a slide valve much closer to the crank, would've served as a combined intake opener and case expander.
If I can't get it working with softer, more, or different size reeds I'll probably put in a valve like that, but it won't be as slick.


Not as slick.
347171
347172


50% of the youtube comments say I need a pipe for backpressure, here it is, not primarily for backpressure though...

347176

[wobbly]

I would say that the 50% saying you need a pipe for back pressure are a solid part of the 90% on FB that talk complete rubbish about Twostrokes.
What does an expansion chamber do to facilitate startup ." Backpressure " is completely irrelevant at that point , though I am very willing to be completely wrong.
But as Jan sucessfully dynoed an Aprillia with no pipe at all ( needed rejetting obviously ) I think I am pretty safe.

[Flettner]

Thankyou Adegnes, good to see real development work happening, not copying or just talk. I am excited about this trapped ring development. Look forward to you showing up all the doubters. Pitty we all have to do this kind of work on a shoestring isn't it.

[adegnes]

I would say that the 50% saying you need a pipe for back pressure are a solid part of the 90% on FB that talk complete rubbish about Twostrokes.
What does an expansion chamber do to facilitate startup ." Backpressure " is completely irrelevant at that point , though I am very willing to be completely wrong.
But as Jan sucessfully dynoed an Aprillia with no pipe at all ( needed rejetting obviously ) I think I am pretty safe.

They're a strange crowd....



Thankyou Adegnes, good to see real development work happening, not copying or just talk. I am excited about this trapped ring development. Look forward to you showing up all the doubters. Pitty we all have to do this kind of work on a shoestring isn't it.

Thanks!
All I need is unlimited money and time, is that too much to ask for!?

Can't get anything done until Sunday night now, social obligations have me pinned down.

[SwePatrick]

You are using methanol fuel, aren't you Patrick? My limited experience with methanol taught me that you must not try to get the plugs dry. The engine will perish before the plugs dry up.

Not in this engine yes, ordinary pumpfuel(in Sweden 98octane, research?)

I tested a thing yesterday to quickly lean the engine, i bought some e85, ofcourse it went really lean directly with 100% 85 and 4% oil.
So i splashed in some 98octane, roughly about 30% petrol, so 70% e85 mixed with 30% petrol.
This started to work actually, just had to pull out the chokes, then it was roughly correct, it idled and responded really good.
The pops ang bangs got less, now it was only above 12000rpm, on 100% petrol it started at ~10000rpm.
So it tells me it was rich on petrol.

It is really hard to get into the ballpark with jetting with hard tuned twostrokes, i got many years experiance, they are really really sensitive, and i use to read the plugs.
Now that tuning tool was diffuse as the pulls were so short.

The engines often sounds really crisp when freerevving, so in comparing to tune a 20hp 125cc it is hard, those 20hp tells me direct what they want.
But high tuning grade makes all diffuse :)

[SwePatrick]

Not in this engine yes, ordinary pumpfuel(in Sweden 98octane, research?)

I tested a thing yesterday to quickly lean the engine, i bought some e85, ofcourse it went really lean directly with 100% 85 and 4% oil.
So i splashed in some 98octane, roughly about 30% petrol, so 70% e85 mixed with 30% petrol.
This started to work actually, just had to pull out the chokes, then it was roughly correct, it idled and responded really good.
The pops ang bangs got less, now it was only above 12000rpm, on 100% petrol it started at ~10000rpm.
So it tells me it was rich on petrol.

It is really hard to get into the ballpark with jetting with hard tuned twostrokes, i got many years experiance, they are really really sensitive, and i use to read the plugs.
Now that tuning tool was diffuse as the pulls were so short.

The engines often sounds really crisp when freerevving, so in comparing to tune a 20hp 125cc it is hard, those 20hp tells me direct what they want.
But high tuning grade makes all diffuse :)

Kind of forget what o wrote about it was better,,,,
I feel like a rookie,, nothing works.
i need to start over.

[adegnes]

Regarding my 100% of bore single exhaust port.
It provides more STA than bridged ports, no doubt, but what about velocity?
Even though there's a slight curve to the top edge + a bevel, it opens the whole duct volume at once, not like a 3-port where the aux's should stay closed a few degrees.
The floor is just slightly below transfer roofs, and duct exit is 75% of effective port area(if I remember correctly).

[wobbly]

A T port at 100% bore as was used in A kit Honda 125/250 GP cylinders had a dead straight timing edge.
This obviously worked very well.
Your 100% port with no bridge , but a much higher floor than the old Honda's had , should have greater duct velocity and work even better.
More so using the reduced duct exit concept as well.

[andreas]

I read it like the effective port area is the whole ex-area, not just the blowdown-which is then reduced to 75%. But what happens when the whole area is more or less the same as the blowdow area?

[F5 Dave]

Dude, glad you've dropped back in.

So have you done cylinder leak tests? Port ideas seem great. But can the rings cope with their primary job after a reasonable period of running?

[adegnes]

A T port at 100% bore as was used in A kit Honda 125/250 GP cylinders had a dead straight timing edge.
This obviously worked very well.
Your 100% port with no bridge , but a much higher floor than the old Honda's had , should have greater duct velocity and work even better.
More so using the reduced duct exit concept as well.

Thanks wobbly, that's what I'm hoping for.


I read it like the effective port area is the whole ex-area, not just the blowdown-which is then reduced to 75%. But what happens when the whole area is more or less the same as the blowdow area?

Been thinking about this too, my duct exit might be too small. Seems fine in simulations though. When things are working I'll cast a few cylinders with more area and compare.


Dude, glad you've dropped back in.

So have you done cylinder leak tests? Port ideas seem great. But can the rings cope with their primary job after a reasonable period of running?

Thanks!
No leak test yet, been mostly focused on if the ring will survive at all. Need to buy/fabricate a tester.
This first batch of rings are too soft, ring gap is growing rapidly.
Might partly be the bore wearing down too, used the wrong type of Boron Nitride in my plating bath, hexagonal vs cubic. Mixed in some Silicon Carbide, next plate will be Nickel/hBN/SC(which I suspect is what's used by several "professionals")


New harder rings in the making. As long as those tabs don't break off these rings should behave and wear just like normal one's I think.
Wonder if composite plating the rings could be beneficial. Can do electroless nickel with whatever small particles I want. Electroless deposits a uniform layer vs electroplating which produces high spots around edges etc.

[dutchpower]

A T port at 100% bore as was used in A kit Honda 125/250 GP cylinders had a dead straight timing edge.
This obviously worked very well.
Your 100% port with no bridge , but a much higher floor than the old Honda's had , should have greater duct velocity and work even better.
More so using the reduced duct exit concept as well.

Wobb from 125cc to 50 cc is complet other bal game

A kit 125 and A kit 250 is totaly different ( pv )

The 75 % on a bidalot 50 exh. prt is totaly bullshit greater then stock will give 23 hp only on the exhaust prt.

[wobbly]

Real A kit RS125s had a PV just like the 250.
Here is a dyno comparison of a real A kit RS125PV ( Tada ) vs a well tuned customer RS125 vs a " not so real A kit " non PV cylinder - easy to see why this was kept in house at Honda.
I dont understand at all the last statement " The 75 % on a bidalot 50 exh. prt is totaly bullshit greater then stock will give 23 hp only on the exhaust prt ". What are you saying ?

[ken seeber]

Thanks wobbly, that's what I'm hoping for.
rings should behave and wear just like normal one's I think.

Alex,
Cuppla thoughts on the ring. As I understand it, you are running the inverted L shaped ring with the vertical section downwards and inside. See pic of how I see this.

347229

From the excess radially outward movement from your vid, it appears that the vertical section has been removed on the ring peg side, but retained on the exhaust side.

Now if this is the case, there are a couple of points that could be made.

1. There is a considerable extra clearance/void volume around the “captured” L ring compared to a simple flat “rail” ring. It is critical that the cylinder pressure can build up here to ensure proper ring sealing, thus this volume must be minimized. The removal of any of the ring material will increase this volume and might detract from obtaining full cylinder pressure behind the ring, potentially causing low compression thru ring seal leakage= bad..

347227

2. The clearance indicated must be such to ensure that the ring can seal against the bore in an extreme piston rocking situation. From the example here, this would need to be 0.3 mm for a 125, say (40/54)*0.3 = 0.22 for square 50.

347228

Keep up the good work on a very interesting & informative project for which you should be very proud considering your “vertically integrated” (ie you do everything) approach.

[adegnes]

Alex,
Cuppla thoughts on the ring. As I understand it, you are running the inverted L shaped ring with the vertical section downwards and inside. See pic of how I see this.

347229

From the excess radially outward movement from your vid, it appears that the vertical section has been removed on the ring peg side, but retained on the exhaust side.

Now if this is the case, there are a couple of points that could be made.

1. There is a considerable extra clearance/void volume around the “captured” L ring compared to a simple flat “rail” ring. It is critical that the cylinder pressure can build up here to ensure proper ring sealing, thus this volume must be minimized. The removal of any of the ring material will increase this volume and might detract from obtaining full cylinder pressure behind the ring, potentially causing low compression thru ring seal leakage= bad..

347227

2. The clearance indicated must be such to ensure that the ring can seal against the bore in an extreme piston rocking situation. From the example here, this would need to be 0.3 mm for a 125, say (40/54)*0.3 = 0.22 for square 50.

347228

Keep up the good work on a very interesting & informative project for which you should be very proud considering your “vertically integrated” (ie you do everything) approach.

Thank you Ken.
You described everything correctly, except the ring has a "T" shape vs. "L".
After grinding there's two ~5mm tabs top/bottom.

Good point about volume behind the ring, it was already excessive without parts of the vertical ring portion removed.

I think a good solution for V2 is a normal ring groove with short slots for said tabs to sit in. That would eliminate the need for a ring peg too.

[SwePatrick]

Now i can start tuning again. :niceone:
I have tried a lot this weekend:
Dual coils(still on video)
Richen the mixture
Leaner mixture
Checked reeds, modified a little.
checked compression
Changed plugs, four different models
Changed plugwires, three different models
Wen´t through the carbs, floatlevel etc etc.
E85 fuel
Petrol

And finally found it, almost ashamed of it..
As the engine is quite fresh and i haven´t got the feeling for what it want´s yet i have been very careful about adding more advance to the timing.
Finally when i had ran out of options, i said to myself f_ck it, so i added 10 more degrees to the advance over the whole curve.(do not compare with 2nd curve on screen)

Result in video. :eek:


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

[wobbly]

I can see on the screen that the base advance is 0* . So is the trailing edge of the flywheel lobe over the center of the trigger pole at TDC. If so , why.
Never seen that before.

[SwePatrick]

If having a longer lobe i have found that one doesn´t need baseadvance.

Say if you are having a 38degree long lobe, your max advance is 38degree´s
And if you are having a 20 degree long lobe your max advance is 20degree´s, but if you setup baseadvance 18degree´s you can set timing to 38 degree´s again.
But you need to advance the rising triggerpoint the same degrees, as the baseadvance actually is just pulling back the virtual falling signal.

I have strobbed it and it seems to work just fine, 30degrees in software is 30degrees on the 'flywheel'.


347235

[ken seeber]

Thank you Ken.
You described everything correctly, except the ring has a "T" shape vs. "L".
After grinding there's two ~5mm tabs top/bottom.


Alex,

You have got us going on rings. So, after the minimal use of powerful drugs, we came up with some thoughts:
1. Use a conventional Dykes ring, flush with the crown edge, but with virtually no tension. This would rely on the cylinder gas pressure to expand and seal the ring.

2. Flat rail ring, but with a pegged inner projection. See pic. With the 2 piece piston, a suitable vertical pin would control the radial movement. Could allow for adjustment by elongating the hole to allow for ring wear. Alternatively a vertical pin permanently installed, via the crown, thru the hole on the ring. Would be a total pain to work with though.

347236
3. Flat rail ring, but with an eccentric centre, the stiffer side against the exhaust. See pic. Hopefully the extra stiffness of that section of the ring will, in part, eliminate some of the bulging.

347238


4. With both of the above 2 thoughts, one must consider how a ring could be made. Over the last year or so, I have fallen in love with wire cutting. See pic of some examples of this I used for the UHV project, 0.2 thick. If using ground (spring) steel, it would need to be chrome plated at the edge, so this would be a hassle. The other option is to go for a more conventional ring material, say F14 cast iron. Would have to be made into ground discs and then wire cut in the case of 2., but simply turned in 3. It has the advantage it can run direct on the bore.

347237

5. Just don’t run a ring and just rely on the huge volume of nitro & oil to do the sealing, ala model plane/boat engines.

[lohring]

We had some bad experiences with ringless pistons in larger than 15 cc engines. Our 35 cc engine originally came with a ringless piston. We tore up all the available pistons and sleeves searching for an oil and break in combination that would work. The manufacturer eventually went back to a ringed piston.

Lohring Miller

[Makr]

Alex,

You have got us going on rings. So, after the minimal use of powerful drugs, we came up with some thoughts:
1. Use a conventional Dykes ring, flush with the crown edge, but with virtually no tension. This would rely on the cylinder gas pressure to expand and seal the ring.

2. Flat rail ring, but with a pegged inner projection. See pic. With the 2 piece piston, a suitable vertical pin would control the radial movement. Could allow for adjustment by elongating the hole to allow for ring wear. Alternatively a vertical pin permanently installed, via the crown, thru the hole on the ring. Would be a total pain to work with though.

347236
3. Flat rail ring, but with an eccentric centre, the stiffer side against the exhaust. See pic. Hopefully the extra stiffness of that section of the ring will, in part, eliminate some of the bulging.

347238


4. With both of the above 2 thoughts, one must consider how a ring could be made. Over the last year or so, I have fallen in love with wire cutting. See pic of some examples of this I used for the UHV project, 0.2 thick. If using ground (spring) steel, it would need to be chrome plated at the edge, so this would be a hassle. The other option is to go for a more conventional ring material, say F14 cast iron. Would have to be made into ground discs and then wire cut in the case of 2., but simply turned in 3. It has the advantage it can run direct on the bore.

347237

5. Just don’t run a ring and just rely on the huge volume of nitro & oil to do the sealing, ala model plane/boat engines.


Good thoughts Ken. I wish I had an EDM.

I used a ductile iron for Alex's rings and the ones in my engine (although I hard chromed the ones in mine).

I was going to use 8620 (not sure what alloy is comparable in your world) carburizing grade steel and mask everything but the face of the ring, and then Nitride it. Getting anyone to do a moly or similar has turned into a dead end on my budget for now.

When I made the first rings for Alex I did a 1mm ring and after I hardening it was way too stiff. The T section adds too much material. I drew the hardness back until it was reasonable. I think going to a .5 mm ring and cutting some of the T away will allow me to keep it stiff and have reasonable wear for this prototype stage.


What do you think?

Makr

[adegnes]

Alex,

2. Flat rail ring, but with a pegged inner projection. See pic. With the 2 piece piston, a suitable vertical pin would control the radial movement. Could allow for adjustment by elongating the hole to allow for ring wear. Alternatively a vertical pin permanently installed, via the crown, thru the hole on the ring. Would be a total pain to work with though.

347236


Nice suggestions Ken, one of them are strangely familiar.


Here's a variation on my "pinned" ring idea.

339223

The ring is located with the hole in the middle of the 100% exhaust port.
The cylinder could be turned 90° to normal orientation and the pin could be pressed(or threaded) into the piston from the underside through a hole in the wrispin boss.
A conventional piston could be used, and as the exhaust side of the wristpin would never encounter any transfer ports, only that side would need to be blocked, maybe even just plugging the pin with something would suffice.

Watcha think? Mumbo jumbo?

I could happily spend the rest of my days failing trying "stupid" stuff.

My neighbor works at a place they do wire cutting(and grinding), if we move away from the partial "T" ring I'll ask how they feel about doing it for me.

Sorry for being so short, really appreciate the input, lots of stuff on the plate atm.

[wobbly]

SwePatrick , yes your system is fine - using a very small rotor as you have.
I spent days , just like you did , years ago trying to discover why my new TZ based race engine was misfiring past 6000 rpm.
It had a new 100mm rotor on it as is used in many Chinese pit bikes.
This had a long ( 45mm ) lobe and I used two triggers.

In deperation I put a scope on the trigger signal , and discovered that the output from the reluctor coil in the trigger would jump up as soon as the lobe front edge passed the pole.
But about 1/2 way along the lobe , the signal was gone.
And as the ECU is designed to be seeing the falling signal off the trailing edge ( where there was no signal ) it got lost.
So I cut the lobe length in 1/2 , down to about 20mm and suddenly all was fine.

Later I discovered Ignitech had a " long lobe " option , but I have never tested this.

One other point regarding your small trigger rotor setup. This is exactly what HRC used on the RS125 factory bikes with a total loss battery system.
They discovered that with the stock crank , and the very small inertia flywheel plate , they lost a huge amount of overev power.
Thus part of the total loss kitset was a new crank , with alot of extra heavy metal around the wheels to get back the inertia lost from removing the flywheel.
VHM made high inertia cranks for the same reason - in effect loosing any advantage in acceleration gained from taking off the flywheel.
This effect was first seen at Queens Uni where Dr Fleck discovered that the same engine made more power on a eddy current dyno with more inertia.
His opinion was that the extra inertia reduced the in cycle speed difference of the crank as it was sped up on the power stroke - effectively slowing down the crank at BDC , thus giving more time to the
transfer STA number in reality.

[ken seeber]

Good thoughts Ken. I wish I had an EDM.

I used a ductile iron for Alex's rings and the ones in my engine (although I hard chromed the ones in mine).

I was going to use 8620 (not sure what alloy is comparable in your world) carburizing grade steel and mask everything but the face of the ring, and then Nitride it. Getting anyone to do a moly or similar has turned into a dead end on my budget for now.

When I made the first rings for Alex I did a 1mm ring and after I hardening it was way too stiff. The T section adds too much material. I drew the hardness back until it was reasonable. I think going to a .5 mm ring and cutting some of the T away will allow me to keep it stiff and have reasonable wear for this prototype stage.


What do you think?

Makr

Mark, Can see you have considered many options. Obviously one main consideration with anything you may want to try is to make it as easy as possible. To me, getting wire cutting is relatively easy, just sandwich the flat stock between two aluminium plates (in my case we had to cos the material was very thin 0.2 mm). Easy for me as I have a buddy that looks after a machine at a local uni, but still relatively cheap and . Just a simple .dxf file. If you can hard chrome the edge and finish it, then this looks the go, for flat rail type rings anyway.

If Alex is experiencing premature wear of the ring, possibly due to the composition of the plating or honing finish, then a chrome edged ring may be helpful.

[SwePatrick]

SwePatrick , yes your system is fine - using a very small rotor as you have.
I spent days , just like you did , years ago trying to discover why my new TZ based race engine was misfiring past 6000 rpm.
It had a new 100mm rotor on it as is used in many Chinese pit bikes.
This had a long ( 45mm ) lobe and I used two triggers.

In deperation I put a scope on the trigger signal , and discovered that the output from the reluctor coil in the trigger would jump up as soon as the lobe front edge passed the pole.
But about 1/2 way along the lobe , the signal was gone.
And as the ECU is designed to be seeing the falling signal off the trailing edge ( where there was no signal ) it got lost.
So I cut the lobe length in 1/2 , down to about 20mm and suddenly all was fine.

Later I discovered Ignitech had a " long lobe " option , but I have never tested this.

One other point regarding your small trigger rotor setup. This is exactly what HRC used on the RS125 factory bikes with a total loss battery system.
They discovered that with the stock crank , and the very small inertia flywheel plate , they lost a huge amount of overev power.
Thus part of the total loss kitset was a new crank , with alot of extra heavy metal around the wheels to get back the inertia lost from removing the flywheel.
VHM made high inertia cranks for the same reason - in effect loosing any advantage in acceleration gained from taking off the flywheel.
This effect was first seen at Queens Uni where Dr Fleck discovered that the same engine made more power on a eddy current dyno with more inertia.
His opinion was that the extra inertia reduced the in cycle speed difference of the crank as it was sped up on the power stroke - effectively slowing down the crank at BDC , thus giving more time to the
transfer STA number in reality.

I suspected i had to long triggers at first so i actually cut them down also ;)
But there was no difference, so i started to look elsewhere
And as it seems it all works now, it was my caution that was the problem :D

And yes i know about the flywheeleffect and overrev, but keep in mind this is a dragbike, overrev isn't important as on a trackbike, i don´t need the couple of hundreds extra rpm in a bend to keep traction or balance, instead i shift gear and aiming as straight as i can :crazy:

I´m trying to keep engine in the happy place, between max torque and peak power, overrevving it will make it hit the next gear away from the max torque.

[SwePatrick]

The trapped ring issue.

First things first, the ring need to rest on a complete flat surface, also should the ring be completely flat on the underside.
Any produding metal will disturb the seal as the pressure from above will creep.

Second thing, you might have to guide the pressure to help the ring seal correctly.
As i noticed in a clip from Alex, only 50psi,, that´s a huge problem there.
You need way higher pressure to get a complete burn.
About 130-170psi, favorable at the upper value and some high octane fuel.

And third thing as been mentioned before, the ring need to be able to hold on to the cylinder and still let the piston rock.

https://www.thn.nl/en/product-line/piston-rings/piston-ring-types

I would say c1 c3 c7 and cl, all with a touch of c9 is what is mostly used.
the more rocking piston the more touch of c9 they should have.

[ceci]

This could become be a high and mighty engine Neil. Are you contemplating a chin-rest on the upper crankcase?:msn-wink:
346393


I guess you already knew him

https://www.moto-collection.org/blog/imperia-350-a-pistons-opposes-1935/
https://www.moto-collection.org/83aHGyq6/wp-content/uploads/Imperia-350-PO-1935-025.jpg

[TZ350]

.
Genius ....

<iframe width="560" height="315" src="https://www.youtube.com/embed/shg6muwjTaU" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

50cc swept volume, 390cc crankcase volume, target 30+ hp. Racing two strokes, they are not air pumps. For mass air flow through the system. It is all about resonance.

[Muhr]

Wonder if it would be possible to implement this technology in a 2 stroke, someone with a lot of time might try!

They claim 15% more compression without detonation, for example


https://www.enginetechnologyinternational.com/news/new-engine/maserati-brings-pre-chamber-ignition-to-the-mainstream.html

347260

[monkeyfumi]

Wonder if it would be possible to implement this technology in a 2 stroke, someone with a lot of time might try!

They claim 15% more compression without detonation, for example


https://www.enginetechnologyinternational.com/news/new-engine/maserati-brings-pre-chamber-ignition-to-the-mainstream.html

347260

It was a question I asked a few pages back. Apparently someone somewhere is working on it, with good results, though details are scarce.

[Flettner]

I guess something like this would be usefull for an OP uniflow combustion chamber.

[Muhr]

It was a question I asked a few pages back. Apparently someone somewhere is working on it, with good results, though details are scarce.

Maserati's patent is more of a poor man's version, without an extra injector unlike what you drive in f1

https://drivetribe.com/p/f1-burning-lean-pre-chamber-combustion-VMyP7dZLRZmQwvUma3ogBQ?iid=MgcjWNIpTq6irMfdxMqxLg

[SwePatrick]

Finally made some progress.
I got the clutch to hold the power, finally.
So now it became measurable power ;)

I also in the middle of testing things rejetted it for E85 fuel, just for insurance against detonating(more octane)
I just took random drill i had that were a bit bigger than the jets in the carb, so i actually dunno the sizes.
Pilotjet likewise *lol*

But i felt that it can take som more fuel as it did 'boooo' a little before hot.
The pulls were made on third gear so they are quite short(3-4seconds), the pipes didn´t build all the heat needed for the engine to pull harder on top, pipes are tuned for 12500rpm on petrol, and as i run e85 i got colder exhausts.
Little bit more fuel and making pulls on 4th och 5th gear, maybe 6th will probably take me north of 80hp at the crank (now 76,3 at the crank) as it will raise the peak rpm.

And the wavy curves tell me it is still some left on the table, as they often smoothes out when you get in the ballpark of what they want.

But still,, good progress! ;)


347296

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/Vs_oagH5vH4" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Two stroke dyno run of a different kind........

[marsheng]

Now I seem to have decent EGT and CHT data coming from my new MyChron5, I'm looking for some guidelines as to how to determine the spark advance based on the EGT and CHT values.

My thinking. If the ignition is slightly retarded and mixture correct, the EGT and CHT would be on the low side.
If the ignition was correct and the mixture was a bit rich, that to would give lower EGT and CHTs.

Can you differentiate between advance and mixture from the readings?

[wobbly]

You are not paid to think , if the spark is retarded the EGT will be high , the CHT low.
That is a relative statement , as at this time you dont know where the tune actaully is.

The raw numbers ie max recall are pretty much irrelevant , its the rate of climb , of both cht and egt as you pull thru the rpm power range that is important.
CHT and EGT climbing in unison means all is good and safe , if you are using fine wire Platinum plugs then as you get close to optimum spark advance the distinct colour change on the earth electrode
will be at about 1/3 up from the weld.
Then as you lean down , the egt rate of climb will slow as you near peak power , and if you go one leaner with no increase in egt , and the cht is still climbing ,then its beginning to deto.

That is where you do a test to see if a little retard will bring the egt max up again.
The idea is to find the minimum advance that will generate max power with a certain fuel flow. Using fuel to cool an over advanced engine will make alot less power than a slightly retarded spark and a lean jet.
But that scenario means the bsfc is high ( Kgs fuel/Hp/Hr ) , and more power is to be found with optimum spark as well as the leanest jet , up to the limit where the egt starts to slow down its rate of climb nearing peak power.

Then of course you havnt even looked at compression.
All 3 of the main ingredients , advance , com , jet are equally important. But one is super simple to ballpark immediately - and that is , if the com and jet are close then the peak power advance will be 15* btdc.
If it makes best power on the leanest allowable jet at 18* advance , then the com is too low , and visa versa.

[F5 Dave]

That's a lot of balls in the air, and presumably I assume Av vs unleaded skews the pitch rich to advance

[marsheng]

You are not paid to think

Am I getting paid? News to me.

Thanks for the reply, exactly what I wanted. I'll see if I can put it into practice this weekend.

[andreas]

https://www.youtube.com/watch?v=tBbnHxrXdTs
Great stuff
Also, those sheet metal cutters from this or the last century are not half bad.

[TZ350]

.
If not "Genius" then incredibly clever and very interesting two stroke project. Impressive work.

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/2pX-QkpPIAA" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

[SwePatrick]

Alex, you should take contact with Mahle and make their blend of nicasil ingredients official, That´s a hard task for you ;)

Going the easy way with a steel liner is like the opposite of your new t-shirts ;)

[F5 Dave]

Needs a cylinder leak test rig. We've covered them about 300 pages ago. Lock the crank with piston above top of ex. That should tell what the seal is really like.

[Frits Overmars]

Needs a cylinder leak test rig. We've covered them about 300 pages ago. Lock the crank with piston above top of ex. That should tell what the seal is really like.Something like this Dave?
347336
You could lock the crank in any position if you so desire, but it might be instructive to 'scan' the cylinder by holding the piston in a number of positions with a long ring spanner on the crankshaft nut. That way you can establish the point of maximum wear.
I also used this method to check whether the piston ring was stuck in its groove, and if so, on what side of the piston, without even opening the engine.
If the ring is stuck, lifting the piston away from the bore because of the inclined con rod angle will also lift the ring off the bore, aggravating the leakage.

[jfn2]

Hi all
My questions are concerning the 'T' shaped, vertical bridged, exhaust port used in some engines, one being the Yamaha YZ125. I believe it was Woobly said with this type of ex port to reduce the area at 1.5 x the bore in the exhaust duct, to only 95% of port area at the bore. My first question is does this still hold? My second is how far down the duct should you blend the 'T' shape into the main stream?
Most of the cylinders I've seen, they've ended it less than half way down the duct. I understand the exhaust wall is fairly thin in some cylinders so another question is can you curve this blending process to try to extend it down the duct? Thank you for any replies. Jeff

[wobbly]

The T port engines respond exactly the same as 3 port , both have large blowdown capability , and need all the help available to keep the velocity up as the piston is lowering from EPO.
In most cases the smallest area should be at the duct exit , the face where the manifold fits on.
A couple of engines I have done have a female spigot as part of the cylinder , in this case I have made a new spigot that presses into that female step , and then forms a new male slip fit for the header to attach to.
The exit area should be 75% of the EFFECTIVE area of the port at the bore - that is the chordal area X the cosine of the duct roof down angle.
In a full noise T port duct the exit should be oval - with the width at the same size as the header diameter.
This means you end up with an ellipse of 42 wide by 31 high if its like an A kit Honda performance capability.
Then the spigot has a transition from this oval shape out to the round header.
The spigot should have its floor colinear with the duct exit angle , and all of the transition angle is done in the roof - this means lifting the header exit centerline some 3mm above
the center of the cylinder duct exit shape.
No steps anywhere - some have reported that steps help mid range power off corners , but if the spigot is lifted then that setup has the same mid power as the steps , but way more top end.

[andreas]

I, thinking there should be a duct exit/min area factor of the blow down area, as opposed to the effective ex area. Is there such a formula?
And why is it the chord area and not the curved?

[wobbly]

You are right - as Frits has pointed out a couple of times , the duct exit area should be tied to the Blowdown STA .
This would be technically correct , but the 75% area guide idea was derived from a huge number of race engine projects finalised in EngMod.
The exit area is tied in fact to the gas speed Mach number , as it turned out virtually all the engines I have done made best power with the duct exit Mach at 0.8 , and this was virtually always seen
with a 75% area ratio or very close to it.

The chordal area is that actually presented to the gas flow , the curved ( arc ) width has no influence whatsoever on the gas flow Mach number or the Cd thru a duct.
You can have say a 40mm Exhaust chordal width port on a 54mm bore or a 70mm bore. The effective duct area will be identical in both cases , but the 70mm bore will have less arc length across that chordal 40mm.
Thus arc widths are of no use at all in port calculations , to establish angle area or STA.

[andreas]

You are right - as Frits has pointed out a couple of times , the duct exit area should be tied to the Blowdown STA .
This would be technically correct , but the 75% area guide idea was derived from a huge number of race engine projects finalised in EngMod.
The exit area is tied in fact to the gas speed Mach number , as it turned out virtually all the engines I have done made best power with the duct exit Mach at 0.8 , and this was virtually always seen
with a 75% area ratio or very close to it.

The chordal area is that actually presented to the gas flow , the curved ( arc ) width has no influence whatsoever on the gas flow Mach number or the Cd thru a duct.
You can have say a 40mm Exhaust chordal width port on a 54mm bore or a 70mm bore. The effective duct area will be identical in both cases , but the 70mm bore will have less arc length across that chordal 40mm.
Thus arc widths are of no use at all in port calculations , to establish angle area or STA.

Thanks Wobbly, The port window as is curved is not fed only from one angle, it would see gas flow from the partial circle between the cord and cylinder wall above also?

[F5 Dave]

Pressure will be equal inside the cylinder, and high pressure at that. It can only squeeze out one port.

[Vannik]

Thanks Wobbly, The port window as is curved is not fed only from one angle, it would see gas flow from the partial circle between the cord and cylinder wall above also?

Yes, the calculation for the flow area in a T-port takes into account the side wall angles.

[andreas]

Vannik, makes good sense.

[Jhonn]

hi all,

I am following this site already for a couple of years but never posted someting. First of all I am dutch and love to work on 2 strokes, I do lots of hands on testing on the dyno, I work mostly on KTM 85-125 engines as I raced one myself. I receltly started using EngMod and just moddeld the SX85 engine, however I get reliable output but I am not 100% sure if all my inputs are OK as the engine does not realy react to adjustents that I tested in real life. So are there people out here that might can help out with some Engmod quistions or want to check my DAT2 file as the software looks realy good but I need to get more expierence with it.

here you can see one of my latest project, I made 125cc KTM cilinder with an RSA-Wobbly duct I also changed the internal radius of the transfer ports and many more.

[lodgernz]

Thus arc widths are of no use at all in port calculations , to establish angle area or STA.

Although the arc width is useful inasmuch as the chordal width can be easily calculated from it, when using a graph paper cylinder to get the port dimensions.

[F5 Dave]

Pressure will be equal inside the cylinder, and high pressure at that. It can only squeeze out one port.
Geez, that didn't make much sense at the end. Dont post after 9pm on a weekend. :innocent:

[wobbly]

Jhonn , the KTM engines have some well designed features , but several years ago i was offerred free engines and parts from the importer to use in our 125 National karting class.
This was due to my TM ( MX ) engines winning everything.
Being given new stuff seemed like a great idea , untill I discovered that a huge amount od work was needed on the transfer radial angles , no so bad , but what killed the whole thing was the
extremely wierd PV setup.
The main blade operates as normal , lifting with rpm , and was easy to repower with a servo electronic drive.
But the Aux ports operate back to front , that is as the main blade is lifting , the Aux drum type PVs open from the top downward.
This is about as idiotic a system as could possibly be imagined , and made PV tuning all but impossible to get working efficiently , as all the initial blowdown pressure is dropped thru the top opening " slit " at
some stupid high timing number - but the main port is still all but closed off.
I thought the cylinder had been assembled wrong at the factory - but no.
So i gave all the engines and parts back - not sure if they still do this dumb setup , if they do they should be shot for being lazy or maybe just being ignorant.
Im not even sure if Engmod can model this correctly , dont want to know really as I would not even try to tune one.

[jfn2]

Wobbly:
Thanks alot for the T-port info. I know you informed us a while back about trying to reach .8 mach with the T-port but couldn't find it. Thanks to all. Jeff

[wobbly]

When doing the Mach in the Ex duct you set the Ex sensor position to the length of the duct, then do a sim run.
Then do another sim run with the sensor set to the length from the end of the rear cone to middle of the stinger nozzle ( say 10mm ).
Then you can look at both the Mach levels at the duct mozzle point and the stinger nozzle by selecting each Mach reading from the two sims.
When close to being optimum , both will approach 0.8 Mach.
ExMach 1 is the duct end and ExMach 2 is the stinger nozzle.

Jhonn - post the pack file here , or send me a PM for my email address.

[Jhonn]

Jhonn , the KTM engines have some well designed features , but several years ago i was offerred free engines and parts from the importer to use in our 125 National karting class.
This was due to my TM ( MX ) engines winning everything.
Being given new stuff seemed like a great idea , untill I discovered that a huge amount od work was needed on the transfer radial angles , no so bad , but what killed the whole thing was the
extremely wierd PV setup.
The main blade operates as normal , lifting with rpm , and was easy to repower with a servo electronic drive.
But the Aux ports operate back to front , that is as the main blade is lifting , the Aux drum type PVs open from the top downward.
This is about as idiotic a system as could possibly be imagined , and made PV tuning all but impossible to get working efficiently , as all the initial blowdown pressure is dropped thru the top opening " slit " at
some stupid high timing number - but the main port is still all but closed off.
I thought the cylinder had been assembled wrong at the factory - but no.
So i gave all the engines and parts back - not sure if they still do this dumb setup , if they do they should be shot for being lazy or maybe just being ignorant.
Im not even sure if Engmod can model this correctly , dont want to know really as I would not even try to tune one.

Thanks Wobbly,
DM is sended to you.

[Condyn]

I believe I understand the principles behind a proper exhaust duct. I am looking for an acceptable method to add a stuffer to the floor of mine. I should add that I am armed with only an oxygen acetylene rig for welding. It works excellent for welding filthy cast aluminum, however I struggle with anything as thick as an exhaust duct. Anyway, I have previously read about somebody attaching a stuffer with screws through the bottom of the duct. One concern I have is an exhaust leak under the stuffer. Curious as to if anyone has a fool proof plan for such a contraption. Much thanks.

[andreas]

I imagine there will be a problem with heat accumulation in the stuffer. But maybe there is a solution to that.

[wobbly]

Adding a stuffer is not a good idea , as it will over heat no matter how its done.
A simple way to do this is to use aluminium stick welding repair rods.
The small diameter rod makes it easy to get into the duct and add material.
The trick is to angle the cylinder downward so that the molten flux runs down over the weld pool.
If you practice you can achieve a pretty good build up without too many porous holes , but even these can be "spot welded " to fill them after basic grinding of the shape.

[Condyn]

Such a brilliant method that I overlooked. Thank you Wobbly.

[TZ350]

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[SwePatrick]

https://www.youtube.com/watch?v=I8h_mRtwhgQ

Just a warmup to see if everythings ready for dynosession upcoming weekend.

I have dynoed 70.1hp to the wheel so far.
Made some updates since then as:
Heat isolated pipes
V-force 4 reeds from banshee
Made sure the throttles opened the throat fully.
New clutch, carbon fiber lined discs from yz250f
E85 fuel with 10% methanol.

[Niels Abildgaard]

I have dynoed 70.1hp to the wheel so far.



The last Aprilia125 powerlimit was 52 horsepower (from memory) and had cost phantasillions to attain.
Let us enlarge all dimensions from that cylinder with cuberoot of two (= 1,26) and make a 250.
In that cylinder blowdown area will be these 1,26 squared (= 1.59) time so big and powerlimit for same state of art will therefore also be 52 times 1.59 horsepower equal to 83 horsepower.
70.1 hp in rural Sweden whith no official support is impressive.
Hold i gang.

[SwePatrick]

The last Aprilia125 powerlimit was 52 horsepower (from memory) and had cost phantasillions to attain.
Let us enlarge all dimensions from that cylinder with cuberoot of two (= 1,26) and make a 250.
In that cylinder blowdown area will be these 1,26 squared (= 1.59) time so big and powerlimit for same state of art will therefore also be 52 times 1.59 horsepower equal to 83 horsepower.
70.1 hp in rural Sweden whith no official support is impressive.
Hold i gang.

When i dynoed 70.1 i used e85 fuel, it can in perfect tune give about 6-7% more power then petrol.
And i aim for about ~80 to the wheel, so if it all goes as planned i´ll be in the nieghbourhood of 83hp on the sprocket as they measured.

I have used a lot of tech from aprilia when i ported the cylinders actually.
So all their money they spent is still making it self worth something, as all we amateurs can copy a lot of Jan Theil´s(and others like Overmars) work and thinking, and actually get a better understanding how things should be, huge props to those guys!

And thanks for the nice words :D

[JanBros]

The last Aprilia125 powerlimit was 52 horsepower (from memory) and had cost phantasillions to attain.
Let us enlarge all dimensions from that cylinder with cuberoot of two (= 1,26) and make a 250.
In that cylinder blowdown area will be these 1,26 squared (= 1.59) time so big and powerlimit for same state of art will therefore also be 52 times 1.59 horsepower equal to 83 horsepower.


only IF you can rev the 250 as high as the 125 :msn-wink:

[F5 Dave]

Don't you just hold the throttle open longer?

Or change down to 3rd from high speed. That'll do it.

[SwePatrick]

only IF you can rev the 250 as high as the 125 :msn-wink:

Remember i earier built on a single cylinder engine.
this project i´m talking about now is a twin, so no problems with revving ;)

[Frits Overmars]

The last Aprilia125 powerlimit was 52 horsepower (from memory) and had cost phantasillions to attain.
Let us enlarge all dimensions from that cylinder with cuberoot of two (= 1,26) and make a 250.
In that cylinder blowdown area will be these 1,26 squared (= 1.59) time so big and powerlimit for same state of art will therefore also be 52 times 1.59 horsepower equal to 83 horsepower.
only IF you can rev the 250 as high as the 125 Niels was correct, Jan.

The bore and the stroke of the 250cc engine are 1,26 x the 125cc-values, so the port areas are 1,26² = 1,59 x the 125cc-values.
And with the port timings of both engines being identical, the angle.areas of the 250cc engine are also 1,59 x those of the 125cc engine.
With the cylinder capacity of the 250cc engine being 2 x the cylinder capacity of the 125cc engine, its specific angle.areas are 1,59 / 2 = 0,794 x those of the 125cc engine.

If the 250cc engine is to have the same Brake Mean Effective Pressure as the 125cc engine, it must have the same specific time.areas.
The specific angle.areas are smaller, so the time factor must be bigger, i.e. the 250cc engine will give this BMEP at 0,794 x the rpm of the 125cc engine.
So the 250cc engine has the same BMEP at 0,794 times the 13000 rpm of the 125cc engine, and it has double the cylinder capacity. You do the math: it's 83 hp @ 10.320 rpm..

I could have kept this story a lot shorter: keeping the same BMEP requires keeping the same mean piston speed, and with a stroke that is 1,26 times as long, the revs need to be 1 / 1,26 times what they were

[TZ350]

Or change down to 3rd from high speed. That'll do it.

Worked for Speedpro.......

[SwePatrick]

https://www.youtube.com/watch?v=62awu4qJsyQ

347441

I struggled for a while as my ego told me there are more power hiding somewhere.
I finally found it , my rearwheel bearings seized.
this makes the disc drag and ofcourse the resistance in the bearing.
Curve below show when it seized.


https://www.youtube.com/watch?v=hGVMuRDAc7c

[wobbly]

After seeing the actual dyno run time , its way way too short.
You need to being doing the actual power inertia runs in a much taller gear , or take 5 teeth off the back.
If you could do a printout showing egt against rpm, you will see that the delta between run start and run end would show the pipes are not getting hot enough.
On my engine dyno settup I have to do at least 3 all gear WOT pulls , then go down to 4th and do the actual power logging run , to get fully repeatable results with real hot pipes.
Also as I have said a thousand times , use a race plug in a race engine , get some R7376 in there so you can read the ground electrode - but again the run time is too short to get any meaningfull result from that as well.
But , despite all that ranting , great result for the beginning of a project.

[SwePatrick]

I know of all that, but i have developed this problem: i don´t have the guts to spin my roller at above 2500rpm, i have balanced it last winter and it feels really good, but i need to overcome the fear, get some trust, babysteps and i´ll get there, never any wrong to have some caution ;)
The pulls are about 4s long as for now, i want them to be about the double.
I need to fix my brake on the roller, i used to use it to make a steady state pull to raise the pipetemp before a powerpull.
I tried with the brake(when it was working) hold the rpm at say ~10000rpm for about 5-10 seconds.
Then rapidly coast down to about 7000rpm and start a pull.

In my other 212cc kawasaki that gained a LOT of power.

[F5 Dave]

I always did some all gear runs (boohoo) when I had the dyno.. more often than not on a new bike taught something . Quite often to do with fuel supply.

[wobbly]

SwePat - do the simple calculation for Hoop Stress on the flywheel.
This will tell you if your balls are telling you the right thing.

[dutchpower]

What is the material off your roller drum SwePatrick

[SwePatrick]

SwePat - do the simple calculation for Hoop Stress on the flywheel.
This will tell you if your balls are telling you the right thing.

As my roller is quite long(870mm) it is quite hard to balance out the dynamic unbalance, but i´m really close actually.
The diam is 292mm with 60mm shaft through.

[TZ350]

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[SwePatrick]

What is the material off your roller drum SwePatrick

It is steel, 870mm long with 60mm shaft through, and three sideplates(one in the middle to hold the shaft from bending, and to get inertia) 40mm thick.
I also filled it with concrete(it´s been debated before in this thread) this to also make the roller 'dead' and don´t create any harmonics in the shaft.
The walls in the roller are 25mm.

The dyno is built so if something happens the roller is 'caged' and probably won´t be any problem.
But, my mind is my problem, it´s like chasing cure for vertigo.

[andreas]

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I hope he remembered to chamfer the port this time.

[Muhr]

And i aim for about ~80 to the wheel, so if it all goes as planned i´ll be in the nieghbourhood of 83hp on the sprocket as they measured.
Is not 53.21nm at 10567RPM 80.07 HP:done:

[jfn2]

Could someone tell me what this ports are used for? I see no reason for them, or how they work. Thank you. Jeff

[Frits Overmars]

Could someone tell me what this ports are used for? I see no reason for them, or how they work. Thank you. JeffThese aren't Boyesen ports because they do not form a direct connection between inlet and transfer ducts.These are just extra inlet ports, adding a bit more port width to the central inlet port. This layout can be used in reed valve inlet systems as in your cylinder, as well as in piston-controlled inlets.

[SwePatrick]

Is not 53.21nm at 10567RPM 80.07 HP:done:

Hehe,, if it was so easy, the software reports torque at crank and hp at wheel, with hp at crank in paranteses.

[Muhr]

Hehe,, if it was so easy, the software reports torque at crank and hp at wheel, with hp at crank in paranteses.

Bummer!
What does the blue line represent? Is that the second pull?

[SwePatrick]

As it reports in this strange way it is actually the torque.

[TZ350]

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[jfn2]

Thank you Frits for your reply. I understand about the 'NON' Boyesen ports. The cylinder I'm showing you is one that I'm thinking about purchasing for a spare and to do some mod work to.
I do not know about the extra inlet ports as to, if they were cast in place or cut after casting. I have not seen other cylinders with these extra ports, so I believe they were added after casting.
Looks like a pretty good job. Also I noticed that the exhaust port was altered (circled in the pics) and was wondering why only this small amount instead of the whole port? This cylinder is from a Kawasaki Kx 65cc engine. I have heard that this engine is blowdown deficient and looking at the pics I think that's correct. I also understand I can widen the wings on the exhaust ports to gain more blowdown. The manual states the exhaust opens at 87.6 degs b/atdc and the A and B transfers at 116.5 degs b/atdc and C boost port at 119.9 degs b/atdc. I can not confirm this or check the deck height because I don't have my engine apart yet, the boy's still riding it. I guess what I'm looking for are some thoughts and opinions about the extra inlet ports and the altered exhaust ports. I have dealt with extra inlet ports before but only on piston port engines where they worked very well. And I can not ask about the height difference in the exhaust port. Bore is 44.5mm Stroke is 41.6mm Con rod is 85mm center to center.

[Frits Overmars]

I do not know about the extra inlet ports as to, if they were cast in place or cut after casting.... I noticed that the exhaust port was altered (circled in the pics) and was wondering why only this small amount instead of the whole port? This cylinder is from a Kawasaki Kx 65cc engine. I have heard that this engine is blowdown deficient and looking at the pics I think that's correct. I also understand I can widen the wings on the exhaust ports to gain more blowdown. The manual states the exhaust opens at 87.6 degs b/atdc and the A and B transfers at 116.5 degs b/atdc and C boost port at 119.9 degs b/atdc. .Those inlet ports look like cast to me. The modifications on the exhaust port are too narrow to contribute much to the blowdown angle.area. Modifications of this kind usually have the purpose of weakening the initial exhaust pulse for the sake of noise reduction, and sometimes for the sake of taming the rate of torque and power rise at the beginning of the power band, to make a bike more kiddy-friendly, which may well have been the reason in the case of this 65cc bike..

[Vannik]

Naming of porting events.

Since starting to look at opposed piston engines where the phasing of the crankshafts are possible I have run into a nomenclature problem. On a conventional two-stroke the blowdown duration is the same as the plugging duration. On a phased OP engine you have four options:


Smaller blowdown than plugging duration,
Same blowdown and plugging duration,
Zero plugging duration, and
Negative plugging duration where the exhaust port closes before the transfer ports.



So what do we call this "negative plugging duration"?
347478

[yatasaki]

I would call it "no short circuit duration"

[Frits Overmars]

Naming of porting events.

Negative plugging duration where the exhaust port closes before the transfer ports.

So what do we call this "negative plugging duration"?
347478Supercharging is already taken (and has a different meaning). Aftercharging, or afterloading, maybe? ('nachladen' exists in German, and 'naladen' in Dutch).

EDIT: not good enough. The word we are looking for must make it clear that the transfers are still open (and hopefully active) and the exhausts are not.
Aftertransfer, maybe?

[ken seeber]

PECTD
Post Exhaust Close Transfer Duration

[Vannik]

The way the OP2T works is making for interesting findings. Mostly obvious but because I never had the opportunity to vary plugging duration independent from blowdown duration I never thought about it:

1. As we shorten the plugging duration the effect of the plugging pulse becomes less and less. So while on a conventional 2T the blowdown STA is critical, on an OP engine the plugging STA is also critical, depending on whether a tuned pipe or a blower is used.

2. When the plugging duration becomes negative (The duration that still needs a name) the better pipe becomes a megaphone, we only want to extract gas and not plug anything back as the transfers keep flowing and filling the cylinder after exhaust port closure.

[flyincat]

How about BONUS TRANSFER or CLEAN TRANSFER?

[lohring]

I'm probably the start of this issue since I've been playing with the opposed piston version of EngMod. I was surprised to find that the power increased as I lowered the exhaust lead from 12 degrees to 4 degrees. I'm going to revisit this with some of the mild modifications I have been making along the way. It's a piston port engine with a tuned pipe designed for peak power at around 18 to 19,000 rpm. I'm in the process of measuring the volumes more exactly in my model. I can then look at the predicted pressures, flows, and Mach numbers with the different leads. We'll see if it looks like real life. So far I'm getting 29 hp at 19,000 rpm from a 60 cc engine.

Lohring Miller

[OopsClunkThud]

is "TDC" in the diagram related to just one crank or is it the smallest volume based on the phasing of the cranks? seems like as displayed it's off the transfer crank in one and the exhaust crank in the other.

[WilDun]

is "TDC" in the diagram related to just one crank or is it the smallest volume based on the phasing of the cranks? seems like as displayed it's off the transfer crank in one and the exhaust crank in the other.

Guess it could be considered "TDC Dwell"!

As for plugging duration, why not simply call it LP or SP (Long Plug or Short Plug) - perhaps expressed as a percentage?

[OopsClunkThud]

how about using plugging duration but get more specific about if it's "exhaust plugging duration" vs "transfer plugging duration" positive value is exhaust, negative is transfer.

[Muciek]

Guys, I'm tired of making cones for pipes by hand (hammering them on pipes and other stuff..) , maybe someone got some drawings for the slip roll ?

[Flettner]

My boat OP engine ran 6 degrees exhaust lead.
Most outings with no tuned pipe just a Rotax aircraft engine muffler and a four into one collector. At one point I built four tuned pipes, all this successfully did was wreak the gear drive, my home cobbled gears couldn't live with the extra torque. The exhaust pistons also suffered, as I had expected might happen.
I was worried I wouldn't have enough time for the reverse plug when the chambers were fitted so hence only six degrees exhaust lead, for an engine with tuned pipes I don't think you should go much more.
Reguarding the exhaust piston thermal issue. My engine had four carburetors, two feed exhaust crankcases, two feed transfer cases. As a transfer carburetor and an exhaust carburetor combined to fill one cylinder I made the exhauat carburetor 66% fuel and the transfer carburetor 33% useing the extra fuel to help cool the exhaust piston.
My new OP has the exhaust case 100% fuel and the transfer case air only. Some cylinder filling advantages can be had like this, an air buffer, done properly.

[wobbly]

JFN2 - as I have said several times before , you are tuning completely in the dark if you dont do the measuring and calculate the inlet piston ports actual power capability.
Now JanBros spreadsheet calculator is available you dont even have to buy EngMod just to see what the STA numbers look like.
I was really surprised a while ago when doing the numbers on a new CPI Banshee cylinder design.
It had such good inlet time area the huge Boyesen ports were not actually needed at all , untill the cylinder was theoretically capable of making over 120 Crank Hp.
As I was shooting for just over 100 CHp , I thought I would test the codes accuracy at that level of tune .
I filled the Boyesen ports with epoxy and did a dyno session to get the ignition and jetting on the money , then simply knocked out the epoxy filler.
Initially it made 102 Hp , with the Boyesens open it lost 4Hp.
Case closed.

[F5 Dave]

. . . .
Case closed.
Ohh Dad joke.

Was the inlet same as my 496 would be? I'm at 99 now in Road spec 10k peak, 35mm carbs.

[Frits Overmars]

Naming of porting events.

Since starting to look at opposed piston engines where the phasing of the crankshafts are possible I have run into a nomenclature problem.....Negative plugging duration where the exhaust port closes before the transfer ports.... So what do we call this "negative plugging duration"?Neels, how about

TRAFEX - transfer after exhaust
TRAFEC - transfer after exhaust closure

Or, when no transfer is involved:

CHAFEX - charging after exhaust
CHAFEC - charging after exhaust closure

Take your pick :D

[Vannik]

is "TDC" in the diagram related to just one crank or is it the smallest volume based on the phasing of the cranks? seems like as displayed it's off the transfer crank in one and the exhaust crank in the other.


I use the exhaust piston crankshaft as the master. And a positive phase angle is by how much the exhaust piston crankshaft leads the transfer / inlet crankshaft.

Somewhere in between the TDC values for the two crankshafts is the smallest volume and the effective TDC. If both crankshafts have the same stroke this effective TDC is halfway between the two. The result of all this is you have to find a new optimum timing value, for now I just add half the phase angle to the timing value specified for zero phase angle.

[Vannik]

Neels, how about

TRAFEX - transfer after exhaust
TRAFEC - transfer after exhaust closure

Or, when no transfer is involved:

CHAFEX - charging after exhaust
CHAFEC - charging after exhaust closure

Take your pick :D

Frits, you are giving me an idea, negative plugging duration will only work with some sort of blower, turbo or super, so what about "Charging duration"?

[Frits Overmars]

Frits, you are giving me an idea, negative plugging duration will only work with some sort of blower, turbo or super, so what about "Charging duration"?It's always a pleasure to hear that I've contributed to an idea, but in this case I hesitate to take any credit.
Doesn't 'charging duration' cover the whole cylinder filling phase, rather than just the phase after exhaust closure?
If you'd call it 'supercharging duration', then yes, I think that would cover it. But we need short words if we want to make them stick.
SUDU? (That reminds me of Sudoku, the kind of puzzle that I use to take my mind off more serious matters :rolleyes:).

[Vannik]

Boost Charging Duration?

[andreas]

Trailing transfer?

[JanBros]

Why don't we call it Voldemort ?

after "the phase who must/can not be named" ?

[WilDun]

Why don't we call it Voldemort ?

after "the phase who must/can not be named" ?

He was that enigmatic wizard of a tuner, who could do just about anything with two strokes (ie of his magic wand) ...... wasn't he? -

Thread is getting sillier by the minute!

[Muhr]

Hi everyone I have my "forgotten" little 50cc project that has been around for a few years. have now decided to make a shifted engine and when I still do, I thought I would use a balance shaft. And if I still make a balance shaft, I can just as well make it a rear mounted rotary valv. Has started scraping together some stuff, including a gearbox gears for balance shaft and a clutch.
Now to the question, are there any guys that have been rebuilt to dry-clutch that i can get some inspiration from on smart solutions?

Edit: Perhaps the easiest thing is to steal gears and cage mounts from a kz (unfortunately, the gears are a little longer)

[wobbly]

Why do you think you need a balance shaft.
On an engine dyno , or sitting on a kart chassis warming up - the difference in perceptible vibration between say a late model RS125 with one , and a CR125 based one , or a KZ 125 is nil , that I can feel.
The small single cylinder 125 engines balanced to around 58% do not need a balance shaft , a 50cc should be even better with way less peak amplitude forces to deal with.

[Muhr]

Thanks Wob

Yes, of course, it would do just fine without a balance shaft. this project is my little sudoku and lacks a bit of a purpose. The engine will most likely be started once in an engine dyno and then placed on the shelf.
The journey is the goal

[SwePatrick]

When i added a balanceshaft on my 212cc kawasaki i used balanceshaft and gears from 'tecate250' ,dunno exact name.
But it made it fairly simple as the gears and the splines were correct,

It made a world of difference, but on a small 50cc the vibrations will never have the same amplitude as i had(as wobbly wrote).
I revved my 66.4bore 61mm stroke to 13200rpm ;)

But it is fun to learn as one travels forward with a project =)

[ken seeber]

Whilst balancing can make things smoother for the rider/driver, in the case of a bike or kart respectively, is there an effective power increase or decrease?

If, in the case of using a balance shaft, we add weight til we cancel out the vertical reciprocating mass. However this produces much higher 90 deg forces which we cancel out with a balance shaft. The balance shaft bearings essentially experience the same increased force as the crankshaft bearings, both leading to more friction, however small.

So, a question can be, does the extra bearing and drive friction offset the possibly parasitic power loss of shaking the frame and rider/drivers balls ?

[wobbly]

WOW , 61mm stroke/13200 rpm = 27M/s .That is EXTREME.
The tradeoff between parasitic oil drag ,bearing friction ,and added inertia Vs smoothness of operation would depend I believe on how clever the balancing was done initially.
If the wheels of the crank had been lightened , then Tungsten mass added toward the outer edge ( as was done at Aprilia ) then the added inertia of the balancing shaft could easily reduce the acceleration rate
by a % greater than the power released by having most of the final resultant forces cancel.

[jamathi]

Whilst balancing can make things smoother for the rider/driver, in the case of a bike or kart respectively, is there an effective power increase or decrease?

If, in the case of using a balance shaft, we add weight til we cancel out the vertical reciprocating mass. However this produces much higher 90 deg forces which we cancel out with a balance shaft. The balance shaft bearings essentially experience the same increased force as the crankshaft bearings, both leading to more friction, however small.

So, a question can be, does the extra bearing and drive friction offset the possibly parasitic power loss of shaking the frame and rider/drivers balls ?

I made the first 125 GP engine with a balancer shaft.
Some people said I was crazy..... it would cause additional friction.....
When I removed the balancer the engine lost 1,8HP
Later ALL 125 GP engines had balancers!!!!

[Grumph]

WOW , 61mm stroke/13200 rpm = 27M/s .That is EXTREME.
The tradeoff between parasitic oil drag ,bearing friction ,and added inertia Vs smoothness of operation would depend I believe on how clever the balancing was done initially.
If the wheels of the crank had been lightened , then Tungsten mass added toward the outer edge ( as was done at Aprilia ) then the added inertia of the balancing shaft could easily reduce the acceleration rate
by a % greater than the power released by having most of the final resultant forces cancel.

The classic assumption has been that inclusion of a balance shaft should enable a lighter chassis structure - which should enhance acceleration.

But - if there is a class minimum weight which is easily achievable, a case can be made for deleting a balance shaft...

In an ideal world with no minimum weight limits, IMO the case is strong for a balance shaft - but it's an interesting question anyway.

[husaberg]

The classic assumption has been that inclusion of a balance shaft should enable a lighter chassis structure - which should enhance acceleration.

But - if there is a class minimum weight which is easily achievable, a case can be made for deleting a balance shaft...

In an ideal world with no minimum weight limits, IMO the case is strong for a balance shaft - but it's an interesting question anyway.

Odd aside from not having a heavier chassis to soak up the vibes ALA NS/RS500 Honda .
i always assumed that the cases could be made lighter with a balance shaft design as they could be thinner as it's exposed to less vibes.


The NSR500 was given a balancer in the big bang period it was left in on the Screamer, Only as it was faster around the circuit with it in.
Likely because in a single crank set up it made it easier to turn as it cancelled out gyro.
But Doohan never cared why, only if it was faster.

I think i recall something also from Wob about CNC cases losing power quicker than Cast or something? Sealing????

[diesel pig]

I made the first 125 GP engine with a balancer shaft.
Some people said I was crazy..... it would cause additional friction.....
When I removed the balancer the engine lost 1,8HP
Later ALL 125 GP engines had balancers!!!!

Do you think the vibrations were affecting the carburator?

[ken seeber]

I made the first 125 GP engine with a balancer shaft.
Some people said I was crazy..... it would cause additional friction.....
When I removed the balancer the engine lost 1,8HP
Later ALL 125 GP engines had balancers!!!!

Jan, cheers for that. Hard to argue against an extra 1.8 hp in 53.2. A useful gain for sure.

[SwePatrick]

WOW , 61mm stroke/13200 rpm = 27M/s .That is EXTREME.
The tradeoff between parasitic oil drag ,bearing friction ,and added inertia Vs smoothness of operation would depend I believe on how clever the balancing was done initially.
If the wheels of the crank had been lightened , then Tungsten mass added toward the outer edge ( as was done at Aprilia ) then the added inertia of the balancing shaft could easily reduce the acceleration rate
by a % greater than the power released by having most of the final resultant forces cancel.

yes,, tell me about it,, =)
And it produced power also, almost 70rwhp
But wristpin and piston lifespan was very short, dunno why :gob::facepalm:
I later reduced the top rpm to 11000 and it produced 64rwhp with ordinary pumpfuel

This engine will be further developed and tested this winter, i´m about to build disc inlet and with a different cylinder(TM racing)
I promise you, it is a experiance to hear that much volume in a single cylinder rev that much, like a ktm65cc but with volumeknob turned to 25(if max were 10) and still had a silencer =)

[dtenney]

WOW , 61mm stroke/13200 rpm = 27M/s .That is EXTREME.
The tradeoff between parasitic oil drag ,bearing friction ,and added inertia Vs smoothness of operation would depend I believe on how clever the balancing was done initially.
If the wheels of the crank had been lightened , then Tungsten mass added toward the outer edge ( as was done at Aprilia ) then the added inertia of the balancing shaft could easily reduce the acceleration rate
by a % greater than the power released by having most of the final resultant forces cancel.

This is an interesting result. Do you have a theory as to why the HP increased with balance shaft? A free 1.8HP is surely nice to have.....

[SwePatrick]

Fear is beeing pushed away, i needed more numbers on a sheet, so what the heck, just klick up one gear. :headbang:
So, these pulls are on 5th gear, did some small adjusts before, i took away some advance and actually added some more oil to the fuel, now 6%
I also set the plug gaps to 1mm from 0.5 i had when i was looking for misfires.

And as expected, the number went up, but i didn´t expect this much ;)
The jerky pull was from cold engine, it stuttered when i was twisting the throttle.

82.4rwhp and 90,8 crank hp together with 60,8Nm


347494

[Muhr]

I'm convinced that Yamaha's factory team
had been ecstatic over 82.4hp at 10492 in the 90s:D

[SwePatrick]

I'm convinced that Yamaha's factory team
had been ecstatic over 82.4hp at 10492 in the 90s:D

Ever tried alcohol fuel?

I dynoed 74.9hp yesterday on 4th gear and before adjusted ignition
And E85 can add about 7-10% power if properly setup, 82.4X0.9= 74.16hp
Methanol can add even more, ive seen up to 22% on an aircooled engine.
So 10% power my blend could probably add onto 74hp, i see no dramatic way off numbers there ;)

[wobbly]

Well I would not have believed many people regarding the effect of a balance shaft being that great, but Mr Thiel I bow to any day of the week.
My comments were based around " needing " a balance shaft , and yes it is a fact that a well balanced 125 , up to 14500 rpm , you cant tell ( feel ) the difference.
But I think I have mentioned before - Dr Fleck at QUB discovered very early in his distinguished time there that the same engine made more power on a dyno with more inertia.
He instrumented the thing and discovered what was then a completely new phenomenon.

More inertia , be it the dyno flywheel or tunsten in the crank wheels , reduces the in cycle speed variation of the crank assembly.
Thus at BDC the crank has not accelerated as much from gas pressure on the piston , and in effect gave the transfers more time ie the all important STA number.
This is a Catch 22 scenario . Up to a certain point the increased inertia adds more power , but then it soon becomes offset by the increased power needed to accelerate the greater mass.
Its a critical system where a small change can tip the effect in favour of each end result quite dramatically.

This was proven again later in 125 GP racing where Honda offerred an A kit option of removing the flywheel and replacing it with just a timing trigger disc , just running total loss battery.
People tried to do this to a standard RS125 , but sadly without the much higher inertia factory kit crank , big fail - no peak or overev Hp at all.
HRC and VHM then offerred a high inertia crank for total loss , but in reality the total loss system had no advantages as the power lost due to the spinning magnetic field needed for the ignition was minimal.

So - In Jans case with his 125 experement , the addition of the balance shaft put the overall inertia closer to optimum . How much power was gained from lower resultant vibration we will never know.

Re greater power loss from CNC cases Vs sand cast . This is easily answered . If you take a lovely looking CNC case and steel shot bead blast it, making the surface look just like a sand cast one - the power is identical.
Speckly surfaces radiate more heat due to more area.

[jamathi]

Do you think the vibrations were affecting the carburator?

Yes, I think so!
But it may also have been less mass, as Wobbly says.
The later Honda's also got a balancer shaft.....
And of course a balance shaft should NEVER run through oil!!!

[TZ350]

.
Well, they make the right sound and they run on Nitrous ........
.
<iframe width="560" height="315" src="https://www.youtube.com/embed/v7hDX6VAFZk" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

[lodgernz]

Speaking of balance shafts...

https://www.facebook.com/maurizio.rinaldi.921/videos/3370373723076539

[andreas]

A while back I was planning to, in the semi-distant future convert the PV centrifugal actuator into a balance shaft- on a 250 single. Good idea or will I soon after this point in time be filling the transmission with broken bearings?

[SwePatrick]

Andreas, my first version was a balanceshaft driven by the flywheel, and my shafts for the weight was 10mm, bearings seized in very very short time.
I had them in oilbath, and the bosses for mounting the oem ignition stator broke, i used them to hold a plate that had one bearing on the inside of the balancer.

With this i´m saying that there are quite some forces oscillating and the small weight you can get room for in that place won´t make much difference.

Later on i made version two, and it´s still working fine.
I used the shaft and drive gear for the 'tekate' 3 wheeler kawasaki 250.
I welded a complete new housing in front under the cylinder.
The balancesaft is hidden from the circulating oil as kawasaki once designed it.

Rgds

[SwePatrick]

https://www.youtube.com/watch?v=_5TbGU3KPyk

look at this series, quite interesting =)

[andreas]

Andreas, my first version was a balanceshaft driven by the flywheel, and my shafts for the weight was 10mm, bearings seized in very very short time.
I had them in oilbath, and the bosses for mounting the oem ignition stator broke, i used them to hold a plate that had one bearing on the inside of the balancer.

With this i´m saying that there are quite some forces oscillating and the small weight you can get room for in that place won´t make much difference.

Later on i made version two, and it´s still working fine.
I used the shaft and drive gear for the 'tekate' 3 wheeler kawasaki 250.
I welded a complete new housing in front under the cylinder.
The balancesaft is hidden from the circulating oil as kawasaki once designed it.

Rgds
Ok, thanks, maybe I better work out a better solution.

[Muhr]

Ever tried alcohol fuel?

No not in an engine but otherwise I am quite experienced .... (Only on weekends of course)
Have never been involved in anything where alcohol is approved.
started making an exel a few years ago to be able to understand better but was no easy story.

[SwePatrick]

No not in an engine but otherwise I am quite experienced .... (Only on weekends of course)
Have never been involved in anything where alcohol is approved.
started making an exel a few years ago to be able to understand better but was no easy story.

I do it almost the other way, Just using it in engines, and twostrokes love it, it´s almost impossible to seize a twostroke on alcohol.
As the exhausttemp is hard to get above ~450 degrees one need to redesign the pipes.
My pipes is designed to run with nitrous in the future, so now without it i struggle to get the temp, and thereby get peaknumbers at lower rpm than usual for my timings(198/132).
They are designed to make peak at 12000rpm at 600c, now i make peak between ~10500-10900rpm a small variation from time to time.
And add to the fact that often,,, very often alcohol adds a lot of power at lower rpm, very common in any engine, ottomotors and wankels also and actually diesels also.
Probably due to cooler inletcharge and resistance to detonation, and lastly oxygen content in fuel.

Best hp gain i´ve seen so far in a twostroke on alcohol is 22%(methanol)

And, wow!
I didn´t understand that excel in any way at all :)

[Flettner]

You are preaching to the converted here. Although my preference is E85. My 350 air cooled Kawasaki will not detonate, no mater what. Partly also due to being able to ramp up ECU master fuel as the engine gets hotter, fuel injected.

[SwePatrick]

You are preaching to the converted here. Although my preference is E85. My 350 air cooled Kawasaki will not detonate, no mater what. Partly also due to being able to ramp up ECU master fuel as the engine gets hotter, fuel injected.

It´s good addiction, alcohol. ;)
It´s hard to go back when you tried it.

Yes, once engine is hot you can add fuel, a lot!
In a car engine i had a couple of years ago, an Opel c20xe engine with turbo(700hp+) i noticed at 78 degree´s in fuel enrichment vs engine temp, i needed to add fuel again to acheive the same lambda.
I also noticed the idle motor altered it´s dutycycle above 78degrees.
It´s like moonshining ;)


E85 is like 'Methanol light' i use to say.
So with Methanol you can add even more then on E85.

But there is a problem with methanol, it is hard to tune with nitrous, E85 is much easier.
That´s why i run this engine on E85, and why i poured in 10% methanol was actually not for power reasons, it was because i didn't have any jets, i tried to lean out the e85 little with methanol as it is a whole other stoich ratio than e85, and they blend well.

An another 'funny' thing, engine cold, the choke if not jetted up from petrol jetting(choke jetting) will make engine run lean when used.
So easier is to squirt in some petrol or use brakecleaner to start it.

[Flettner]

Note the petrol squirt to start, E85 fuel, TPI
Yes I also noticed this need to ramp up fueling at approx 70 degrees. Lucky there is a fueling graph in the LINK ecu specific for this.

https://youtu.be/CnIemdISKrM

[Muhr]

And, wow!
I didn´t understand that excel in any way at all :)

I understand that! was more of a thought knocked down in an execl. tried to make it a little more understandable. I might be completely off.
However, not how intake temp is affected by different fuel mixes. maybe someone who can figure it out.

[diesel pig]

Is it possible to use a EGT gauge and a long road to tune the mid-range (slide, needle) on carburated 2 stroke? If one does not have ready access to a braked dyno and gas analyser.
For example, doing a third gear run for ½ km with the throttle held at ¼ throttle then another at ½ throttle and then at ¾ throttle while monitoring the EGT temps?
Or would I be better off doing the same runs as above but with plug chops?

[Muhr]

Took some old Otto cycle numbers and put in, does not feel completely crazy

[SwePatrick]

Took some old Otto cycle numbers and put in, does not feel completely crazy

Ratio 6, that is air/fuel ratio?
You can run richer for more coolingeffect as methanol has a wider 'tunerwindow' so to speak.
You are able to run way rich without loosing much at all.
In aircooled engines this is a very good option as they need all the cooling they can get.

And E85 is known to beeing able to give you 7-8% percent more power than ordninary pumpfuel, so that´s about correct.

[wobbly]

EGT Tuning. Short answer to that question is NO.
First main point is that you never run an engine in 3rd gear at 1/4 or 1/2 or 3/4 for any distance - ever.
So what does the info you gain actually mean , nothing , as who knows what the egt " should " be at that rpm/load/throttle position - no one .

You can tune , real close , the idle circuit and the slide/needle/tube up to about 1/2 throttle very easily.
With the engine only just warm , you can immediately tell if there is any lean point in that range when opening the throttle very quickly.
If it doesnt rev faster than your hand opens the slide - its lean.
Start first with screwing in the air screw right in to 1/4 turn - if this fixes the initial bog , then the pilot is too small.
You should be able to have no bog , on transition off idle , with 1 1/2 turns and the correct pilot.
Then start at 1/4 throttle and do the same thing - if it wont pull up off this point faster than your hand then the slide is too lean , and or the tube too small.
The decision to change either the slide or the tube/needle parrallel is finally decided by what happens later in the tuning process.

All this initial "cold " tune , for the bottom end , can then continue with a hot engine , but with it loaded up by the rear brake - again any hesitation or bog at any point means its lean.
Assuming you have already got the main in the ballpark , then the final tube/needle combo is decided by what happens under full load in top gear , when you back off to 3/4 throttle.
If the egt stays the same or rises at all , then either the needle tip is too big , or the tube is too small.
This part of the tune is the most dangerous to the piston , and your health , so be carefull , as you are now at a point where it can be so lean that deto starts - and that can make the egt drop.
In a kart , this test can be done on the stand , but a bike rear brake generally wont have enough load capability.

Of course if the 3/4 test involves making the tube bigger - then this will affect the 1/4 tune , and the slide may need to be changed back to a leaner setting ( or a fatter needle parallel ) - if the thing smokes like hell off the bottom.
As someone said the other day about egt tuning - there are a heap of balls in the air with so many options that interact , but getting the 0 to 1/4 correct , then WOT back to 3/4 correct will be a good baseline.

[diesel pig]

Thanks for the reply Wobbly. My engine is running well on the main jet but as you descride in the third paragraph of your reply when I roll off the throttle to 3/4 to 1/2 it hesitates badly and will not respoled to the throttle until it is on the main jet at full throttle. I will print out your reply and have it with me when I am next tuning my engine. Cheers

[flyincat]

This one is in honor of Frits, continually beating resonance into our heads! Thanks Frits, Wob, Jan, others.. It's one of the best visualizations I've seen showing the power of vacuum and compressed air, and of course some resonance.

Start around 4:50 for resonance visualizations...
https://www.youtube.com/watch?v=nIL3HN4PQlI

[Frits Overmars]

This one is in honor of Frits, continually beating resonance into our heads! Thanks Frits, Wob, Jan, others.. It's one of the best visualizations I've seen showing the power of vacuum and compressed air, and of course some resonance.
Start around 4:50 for resonance visualizations...
https://www.youtube.com/watch?v=nIL3HN4PQlII love it! :2thumbsup

[wobbly]

So here is the result of correct resonance in a 2T.
The intake length is correct ( for the selected rpm ) when the wave bouncing up and down from the reed tip , to the bellmouth end goes above atmospheric at the same time as the
case goes below. This puts + pressure ratio on one side of the petals , and - on the other side , thus opening them as fast as possible.

The Exhaust length is in resonance with the Ex Port timing , when you get Superposition - that is the return wave has the port sitting well above atmospheric ( zero pressure ratio ) when the piston cracks open.
Thus the new high pressure ratio wave is added to the remnant wave , giving a much higher ampltude to the subsequent wave travelling down the diffuser.

Sonic Supercharging.

[andreas]

So here is the result of correct resonance in a 2T.
The intake length is correct ( for the selected rpm ) when the wave bouncing up and down from the reed tip , to the bellmouth end goes above atmospheric at the same time as the
case goes below. This puts + pressure ratio on one side of the petals , and - on the other side , thus opening them as fast as possible.

The Exhaust length is in resonance with the Ex Port timing , when you get Superposition - that is the return wave has the port sitting well above atmospheric ( zero pressure ratio ) when the piston cracks open.
Thus the new high pressure ratio wave is added to the remnant wave , giving a much higher ampltude to the subsequent wave travelling down the diffuser.

Sonic Supercharging.

I gather this shows a third harmonics intake setup, it comes natural or it's the preferred one?

[jfn2]

OK Wobbly
In your opinion where would you set these resonance events?
Intake resonance at peak torque rpm and exhaust resonance at peak HP rpm ?
Or intake resonance and exhaust resonance at peak HP rpm?
Or intake resonance and exhaust resonance at peak torque rpm?
Or somewhere in-between?
Or, as an after thought, would you set the intake resonance for the dip in the power curve that is seen on most 2-strokes?

[Flettner]

Ok, we have talked about this before, RK tech heads.
With the crinkle cut combustion chamber. Kels the RK designer says the design is patented. I ask him repeatedly to explain how it works, no problem with giving away secrets as, like he says, its patented. Can not get an answer. Intetesting that customers are more than happy to shell out dosh not knowing (or careing to know) how it actually helps combustion. It is an old idea so I do wonder about the patent. Those that use it swear by it, is it just because they spent a lot of dosh on it or is it because of its pretty anodised surface?
Why are people so keen to spend money on somthing thats workings appear unexplainable? And if you have a peice of technology that works but you dont know why, where to from there? Its as good as useless.
https://youtu.be/MIWaJe2tYWo

[wobbly]

Andreas , yes that graphic shows a 3rd harmonic resonannce , and the 3rd is prefferred due to a couple of important characteristics .
I have found that the third , with several " bounces " per cycle has the best combination of amplitude Vs band width of effectivness.
This harmonic also has the most reasonable physical length for the rpms we use the most.
In a 125 race engine with peak torque around 12,000 say - the length ( using 2/3 of the reed petal + correct bellmouth end correction ) is around 125mm. Fits in easily with usual carb lengths.

This works well over about a 2000 rpm band - and if tuned to peak torque it does in fact help the 2T common power dip.
But - intake tuning ( super effective in efficiency with a 4T ) has only probably 20% of the tuning "power " to be had compared to the pipe.
This is why an intake boost bottle is nowhere as good as an Exhaust boost bottle in helping mid range power , under the pipe.

The first harmonic would not fit in a bike or kart , though would give a bigger boost in power , but over only a 500rpm range.
Knowing this makes me sad ( annoyed ) that huge numbers of "tuners " think that because the intake on a 250cc MX engine was built to fit into the same space ( reed block to shock spring )
that having the same intake exactly as a 125 ( carb and manifold ) is somehow " OK " , even though the engine peaks over 2000 rpm lower.

Pipe superposition tuning is highly effective , and can be used to dramatically change the character of a race engine.
For high speed road racing type use , then having the effect start just under peak power , then keep working well into the overev , gives the best result.
But for wider range MX use , or in cases where the gearbox ratios have bigger drops ,then having the effect start below peak torque and continue up to peak power is the most usefull.
This can be made even more efficient by using the fact that Ex timing duration around 190 * gives the greatest superposition amplitude / bandwidth.
That is only possible where it is not absolutely necessary to have huge Blowdown STA to support really big bmep numbers.

[teriks]

Ok, we have talked about this before, RK tech heads.
With the crinkle cut combustion chamber. Kels the RK designer says the design is patented. I ask him repeatedly to explain how it works, no problem with giving away secrets as, like he says, its patented. Can not get an answer. Intetesting that customers are more than happy to shell out dosh not knowing (or careing to know) how it actually helps combustion. It is an old idea so I do wonder about the patent. Those that use it swear by it, is it just because they spent a lot of dosh on it or is it because of its pretty anodised surface?
Why are people so keen to spend money on somthing thats workings appear unexplainable? And if you have a peice of technology that works but you dont know why, where to from there? Its as good as useless.
https://youtu.be/MIWaJe2tYWo
That looks very much like its been turned in a lousy setup causing a huge amout of chatter..
It had different squish and increased compression though, so would for sure run different than the original.
I can not see how the effectively terrible surface quality could help in any way though.

[Muciek]

There was a video of milling similar or same thing, it looked like it was programmed to do it as fast as possible ... https://www.youtube.com/watch?v=7Me6EjloqLI&feature=emb_logo

[andreas]

Very interesting Wobbly

[Flettner]

There was a video of milling similar or same thing, it looked like it was programmed to do it as fast as possible ... https://www.youtube.com/watch?v=7Me6EjloqLI&feature=emb_logo

Making that surface is easy enough with a CNC mill, but why would you?
My only thought is, I need to get into this market because you could produce anything, paint it red, talk some bullshit and sell heaps of them.
I just can not understand how people will buy somthing like this but not know or care how it works or is that just me, do I have the problem? ��.

[wobbly]

You are right Flettner. I had a huge argument with RK several years ago , as he simply refused to provide any evidence whatsoever in a back to back dyno test that the " crinkle cut "
head with identical squish and CC made any difference in power.
And here in the video , once again , we have a stock head that is being replaced by a RK mod version with 1/2 the squish depth and obviously higher compression .
The guy even measured the chamber shape ( not the actual cc as would have been way more scientific ) and I would guess its probably at a minimum up one com point .

If I did a head with 1/2 the squish depth ie 1.8 down to 0.9 , and went from say 13:1 to 14 : 1 com ratio OFF COURSE it will have way better throttle response , feel good for a butt dyno , and would show a good gain
in a real dyno shootout.
This is COMPLETELY FUCKING OBVIOUS , but seems to escape all the Merican Catalogue Buying Warriors.

The crinkle cuts would reduce somewhat , the added flame front turbulence created by the higher MSV , and add heat soak/reflection area to the squish band thus inducing deto .
Those are comments made from a lifetime of experience in trying to increase the first factor , and trying just as hard to reduce the second.
Am I a narcissistic wanker , of course , just ask RK or NoLuc for completely unbiased opinions on that.

[F5 Dave]

Thing is, you can't dyno test anodising.

You can however remove it, much to my pleasure I found last weekend removing the blue off the Chinese YZ kickstarter for my Red GasGas.. some Selley's oven cleaner gel for a few min, scrub, repeat.
Joy.

[jfn2]

Wobbly
Thank you very much for your response about the intake and exhaust resonance and where best we might use them on different types of engines. I believe I recall Blair said the 3rd harmonic resonance worked the best. Since snowmobiles have a fair amount of room and with a centrifugal clutch you might use the first harmonic resonance?
In the old days the RK head would fall into the category of snake oil and the men that sold them were called snake oil salesmen and believe me some of them were very good at talking you out of your money. Had one tell me that putting grooves in the crank wheels would gain 1 or more HP by atomizing the fuel better. We could find no gain on the dyno.

[F5 Dave]

Ahh, but were the grooves Counter rotating or Contra rotating? (?!!?)

Dyno = where Optimism meets Murphy's Law.

[koenich]

the MX industry is full of big claims with no proofs.

Ever seen a dyno chart directly from FMF or some other company selling 'tuning' parts? Yet they sell like crazy and the only feedback you find is "revs to the moon" or "pulls like no other" - if your wallet is 500$ lighter of course that exhaust changes the world for you...

[husaberg]

the MX industry is full of big claims with no proofs.

Ever seen a dyno chart directly from FMF or some other company selling 'tuning' parts? Yet they sell like crazy and the only feedback you find is "revs to the moon" or "pulls like no other" - if your wallet is 500$ lighter of course that exhaust changes the world for you...

Pipes are one of the few i would say are dyno'ed
here is a tour of Pro Circuit

https://www.youtube.com/watch?v=pEFMXPd1iDM
https://www.youtube.com/watch?v=aCXPZ3vkKNY

FMF
https://www.youtube.com/watch?v=lYmyAzRB-ts https://www.youtube.com/watch?v=jJ8Iwrz-WmU

https://www.youtube.com/watch?v=D1X-t-tO_pk
https://www.youtube.com/watch?v=lC8wxcNq5Pg

[koenich]

sure, sometimes they are by magazines. but if you want to sell say a pipe, why not post the dyno chart on your webshop? none of the big companies does this, just some words they'll spread the power band blabla and revs to the moon. Tyga has one on their page and one of the most beautiful (but also expensive) pipes for a YZ250: http://tyga-performance.com/product_info.php?cPath=72_1047_1278_1279&products_id=3867

Flettner, get into that business. But absolutely necessary to anodize parts :tugger:

[husaberg]

sure, sometimes they are by magazines. but if you want to sell say a pipe, why not post the dyno chart on your webshop? none of the big companies does this, just some words they'll spread the power band blabla and revs to the moon. Tyga has one on their page and one of the most beautiful (but also expensive) pipes for a YZ250: http://tyga-performance.com/product_info.php?cPath=72_1047_1278_1279&products_id=3867

Flettner, get into that business. But absolutely necessary to anodize parts :tugger:

Here is their Dyno room at 8 minutes

https://www.youtube.com/watch?v=jJ8Iwrz-WmU

Cool Yoshimura factory tour complete with photos of Croz

https://www.youtube.com/watch?v=zlmyVuWi2JA

Akvrapovic tour

https://www.youtube.com/watch?v=giGF5ZV8USc&t=28s

[koenich]

sure Husa, I have no doubt they all have dynos (or at least hope) and some capable operator. my point was that they don't advertise with results but rather some words. as Wob said, Murican shoppers is all you need...just browse through VitalMX forum :facepalm:

[Frits Overmars]

Ok, we have talked about this before, RK tech heads with the crinkle cut combustion chamber....
Why are people so keen to spend money on something thats workings appear unexplainable?Halve the squish clearance, reduce the combustion volume and add something the customer can actually see, and you're in business.
Next year you can omit the crinkles, use a different anodizing color, and business will be better than ever :whistle:
347554

[husaberg]

sure Husa, I have no doubt they all have dynos (or at least hope) and some capable operator. my point was that they don't advertise with results but rather some words. as Wob said, Murican shoppers is all you need...just browse through VitalMX forum :facepalm:

I am sure there is lots of that. There are hundreds of other dubious go faster goodies to there to take weekend warriors money. that want shiny magpie parts
But for pipe manufacturers, it would be waste of time to advertise hp as the next company would just say they make 1 hp more to try and get sales not only that the pipes have to work with all the other mods.
FMF and Pro circuit are professional organizations that sell on race results.
MX races are not often won in the dyno room. They are won based on what is faster around the track for an entire race.
There was an ad that ran for years for a US pipe maker that showed his butt dyno that worked off lap times. Bassini

[Muhr]

Now to the question, are there any guys that have been rebuilt to dry-clutch that i can get some inspiration from on smart solutions?

Edit: Perhaps the easiest thing is to steal gears and cage mounts from a kz (unfortunately, the gears are a little longer)

Today a friend was over and left an old bottom end with a dry clutch that he had lying around, gave up the idea of rebuilding a wet clutch when he had one. Also got a little cute rod for the project.


Ratio 6, that is air/fuel ratio?

And E85 is known to beeing able to give you 7-8% percent more power than ordninary pumpfuel, so that´s about correct.

Yes. The stated numbers are from manufacturers the optimal amount for maximum combustion, it is possible to adjust all values based on your preferences.
Engine numbers are only schematic and should be adjusted. the idea was to find a way to define the minimum octane, which is quite reservatively done.

[lohring]

Model engines used a combustion chamber with much more limited cuts. The idea was to improve scavenging. Both the origonal designer and the manufacturer who "borrowed" the idea claimed around 1000 more rpm.

Lohring Miller

347558347559

[Condyn]

I have an air cooled twin engine that shares the same bore and stroke as a more modern liquid cooled engine. The liquid makes very good power. I am essentially taking most characteristics from the liquid and applying them to my anemic air cooled turd. I have ground off the Cooling fins around the exhaust duct and welded up the area for auxiliary exhaust ducts before welding fins back on. Also welded up the floor and the bottom corner radii with aluminum sticks ( thanks for the tip wobbly ) will be doing the 75% nozzle on this and reshaping the duct to oval. The air cooled is a cylinder reed with very little intake area and no good way to add larger reed blocks due to the design limitations and rear studs. I know... I know I could cut the pistons and so on but I would rather have a nice inner transfer radius and a case reed air cooled. I have cut the reed blocks off of the liquid engine and am planning on welding them to the air cooled engine. Even though the bore and stroke is the same, the liquid has a taller case and shorter cylinder than the air cooled counterpart, due to the intake design amongst other reasons I am sure. There is not enough room between the crank bearings on the air cooled engine with the shorter upper case half ( the case splits horizontally ) for the liquid reed blocks to have straight unblocked flow into the crank case. The rectangle area of the aluminum after the pedals on the reed blocks is 2480mm2. If I keep the height the same and reduce the width to the width of the case between the bearings it would be 1953mm2 at the case. My idea was to make the reduction in width with a block of aluminum welded between the reed blocks that I cut from the liquid engine and the air cooled case. I know this would also add to the case volume and or intake length? ( If that makes sense to anyone I will be surprised ) This finally leads me to my question. Is it acceptable to have a smaller intake area after the reed petals at the crankcase, or would it be a better idea to transition the rectangle into a square of the same area? I ask this because I know the inner area of the reed block already is not the same as what is going through the reeds.

[wobbly]

You need to be looking at the effective window area of the reed block - having alot of extra area after the reed windows does not aid pressure recovery.

[andreas]

I have an air cooled twin engine that shares the same bore and stroke as a more modern liquid cooled engine. The liquid makes very good power. I am essentially taking most characteristics from the liquid and applying them to my anemic air cooled turd. I have ground off the Cooling fins around the exhaust duct and welded up the area for auxiliary exhaust ducts before welding fins back on. Also welded up the floor and the bottom corner radii with aluminum sticks ( thanks for the tip wobbly ) will be doing the 75% nozzle on this and reshaping the duct to oval. The air cooled is a cylinder reed with very little intake area and no good way to add larger reed blocks due to the design limitations and rear studs. I know... I know I could cut the pistons and so on but I would rather have a nice inner transfer radius and a case reed air cooled. I have cut the reed blocks off of the liquid engine and am planning on welding them to the air cooled engine. Even though the bore and stroke is the same, the liquid has a taller case and shorter cylinder than the air cooled counterpart, due to the intake design amongst other reasons I am sure. There is not enough room between the crank bearings on the air cooled engine with the shorter upper case half ( the case splits horizontally ) for the liquid reed blocks to have straight unblocked flow into the crank case. The rectangle area of the aluminum after the pedals on the reed blocks is 2480mm2. If I keep the height the same and reduce the width to the width of the case between the bearings it would be 1953mm2 at the case. My idea was to make the reduction in width with a block of aluminum welded between the reed blocks that I cut from the liquid engine and the air cooled case. I know this would also add to the case volume and or intake length? ( If that makes sense to anyone I will be surprised ) This finally leads me to my question. Is it acceptable to have a smaller intake area after the reed petals at the crankcase, or would it be a better idea to transition the rectangle into a square of the same area? I ask this because I know the inner area of the reed block already is not the same as what is going through the reeds.

Your "smaller" area of 1953mm2 is equal to a 50mm duct. In what engine is this maybe not enough?

[Condyn]

Your "smaller" area of 1953mm2 is equal to a 50mm duct. In what engine is this maybe not enough?
Im not quite sure what you mean by that. The 2480mm2 would be closer to a 50x50 window than the 1953mm2. One reason that I asked is because it would be quite a steep transition in a short distance.

[andreas]

Im not quite sure what you mean by that. The 2480mm2 would be closer to a 50x50 window than the 1953mm2. One reason that I asked is because it would be quite a steep transition in a short distance.

50mm round duct I mean, but its still quite big. Does the reed open more than 1953mm2? And the carb is also bigger, then this number is too small.

[Condyn]

I definitely do not want to accept this reed block as the end all be all solution just because of the success that the liquid I am referring to has had. Maybe a smaller unit would work better. I do have Engmod2t but I want to physically build this engine and dyno it before I complete my model and simulate it. I think it will help me develop it more effectively that way. I will try to grasp the pressure recovery idea.

[wobbly]

So if you have EnMod , then its easy to calculate the effective reed window area.
This is the important factor to be looking at to see if the reed itself will be deficient in area to a) match the carb size b) match the area needed for the power predicted.
If the reed is deficient , then the obvious step is a VeeForce W reed.
Part of the reason these work well is that invariably their much bigger window area is fitted into the original reed cavity area - and with a much less abrupt area increase exiting the reed tips this
helps the pressure recovery.
Making the reed cavity exit area into the case , smaller and smaller has been a trend over the last several years.

[Muhr]

I have been sitting this weekend and going back and forth regarding how to handle the lubrication of the angle gear for the rotary valve.
As I see it, there are 3 options.
1. Handle lubrication for this part separately from main oiling.
2. Make it a part of the crankcase
3. Couple it with main lubrication through a passage for oil and one for vent.
These variants all have different pros and cons, with amount of shaft seals, etc.

Anyone done any similar solution?

[SwePatrick]

Is it possible to use two different materials?
Like steel in one gear and sintered in the other.
I was thinking, it's like no load/forces on that axel.

https://www.ascosintering.com/bevel-gears
https://shop.hpceurope.com/an/produit.asp?prid=4386

[wobbly]

SwePatrick - that is a dangerous asumption as the Aprilia would break the RV drive shaft when certain numbskull riders would try to use the engine braking ( breaking ) like a 4T and
change down gears , instantly hitting 14500 rpm. The inertial loads from spinning up even a carbon disc are considerable.

My take on the drive setup would be a seperate small enclosed space with a seal on each end of the cross shaft.
That way the you would have a minimal oil bath needed for the bevel and the LH bearing behind the balance disc only ( the balance disc does not need oil splash at all )

Myself and Jeff Henise are looking at the same scenario for a 500 parallel twin with two RV across the front , needing individual discs as it runs 90* firing.

[Flettner]

are you not better off just running two crankshaft disc valves, one either side.
Or in the case of a twin, make it a V, one crankshaft disc valve per crankcase and a butterfly that opens the the case, opposite side, 24 / 7 when up at full power. A V allows room for this.
And of course four injectors per cylinder. (mk2)
I guess no reason not to do this as a single cylinder also, there by only needing one disc valve on one side, as per tradition.

[ken seeber]

I have been sitting this weekend and going back and forth regarding how to handle the lubrication of the angle gear for the rotary valve.
As I see it, there are 3 options.
1. Handle lubrication for this part separately from main oiling.
2. Make it a part of the crankcase
3. Couple it with main lubrication through a passage for oil and one for vent.
These variants all have different pros and cons, with amount of shaft seals, etc.

Anyone done any similar solution?

Muhr,
Without a full understanding of the design, I would think that the shaft bearings and gears could all be lubricated using the transmission oil. This would necessitate some careful design of angled channels and drillings to ensure the oil gets around. If you had the one (& only) seal behind the bearing adjacent to the disc valve, this bearing would have to be lubricated. Not sure on the overall angling of the unit, but possibly a drilling from the B port crankcase passage might be sufficient to create some flow. Maybe there is enough oil (from the mixture) migrating to the centre of the disc to get into the bearing.

Some nice features in the design.

[wobbly]

Been thru all the options for a twin Flett , a V cannot ever get anything like symetrical intake and Exhaust geometry.
The KTM250 GP parallel twin engine running at 90* , with a balance shaft was I believe the best compromise for performance and KISS.
Just add RVs driven by the balance shaft , and provision for Mk2 then it has the best of all the current ideas.
Using the gib system on the RVs we can achieve virtually any open duration we want ( of course not 24/7 ) but from my experience of running at 95* closing the gain in top end
and overev power is huge.
Of course then the mid power is non existant , but with servo control of the opening and closing angles this wont be an issue.

[wax]

Reading back through the posts I came upon a part where you were talking about y-manifolds and how it can supercharge the other cylinder as the exhaust gases come out the port. This was only at 200 degrees of exhaust or above. Do you think this is much better than the 190 degree superposition on the same exhaust system

[SwePatrick]

SwePatrick - that is a dangerous asumption as the Aprilia would break the RV drive shaft when certain numbskull riders would try to use the engine braking ( breaking ) like a 4T and
change down gears , instantly hitting 14500 rpm. The inertial loads from spinning up even a carbon disc are considerable.

My take on the drive setup would be a seperate small enclosed space with a seal on each end of the cross shaft.
That way the you would have a minimal oil bath needed for the bevel and the LH bearing behind the balance disc only ( the balance disc does not need oil splash at all )

Myself and Jeff Henise are looking at the same scenario for a 500 parallel twin with two RV across the front , needing individual discs as it runs 90* firing.

Ofcourse you need to take in calculations using a bit beefier then normal.
I thought everyone was smart enough to compensate for that ;)

If it is possible to get it to work on big v8 engines(brass gear on distributor), i would think it´s possible to get it to work on a small shaft with a carbondisc in the other end.
You seen a distributor and it´s huge rotor?
Quite big inertia in those(even thou it´s plastic), and i have never seen any gear suddenly break due to tireshaking(high intense shaking in whole driveline, huge clatter in gears), they get worn by mileage as everything is anyway.

Seems to be the interwebs these days, to blow up a small problem to a huge one.

[Muhr]

My take on the drive setup would be a seperate small enclosed space with a seal on each end of the cross shaft.
That way the you would have a minimal oil bath needed for the bevel and the LH bearing behind the balance disc only ( the balance disc does not need oil splash at all )

Myself and Jeff Henise are looking at the same scenario for a 500 parallel twin with two RV across the front , needing individual discs as it runs 90* firing.

Thanks wob
I can only agree that it is the most straightforward approach.
Hope to hear more about the 500 project! Sounds very interesting.


Muhr,
Without a full understanding of the design, I would think that the shaft bearings and gears could all be lubricated using the transmission oil. This would necessitate some careful design of angled channels and drillings to ensure the oil gets around. If you had the one (& only) seal behind the bearing adjacent to the disc valve, this bearing would have to be lubricated. Not sure on the overall angling of the unit, but possibly a drilling from the B port crankcase passage might be sufficient to create some flow. Maybe there is enough oil (from the mixture) migrating to the centre of the disc to get into the bearing.

Some nice features in the design.

Thanks Ken
Yes it would have been neat to be able to get this part can maintenance itself from the already existing lubrication. Made a sketch of using balance shaft gear as a pump, maybe a little too optimistic ..


Ofcourse you need to take in calculations using a bit beefier then normal.
I thought everyone was smart enough to compensate for that ;)

If it is possible to get it to work on big v8 engines(brass gear on distributor),

Seems to be the interwebs these days, to blow up a small problem to a huge one.

Questions one should ask yourself are how fast it spins and how fast it changes speed

https://en.wikipedia.org/wiki/Jerk_(physics)

[Frits Overmars]

are you not better off just running two crankshaft disc valves, one either side.That is what Jan Thiel would prefer now, based on his experience with the rear-disc-valve RSA.


Reading back through the posts I came upon a part where you were talking about y-manifolds and how it can supercharge the other cylinder as the exhaust gases come out the port. This was only at 200 degrees of exhaust or above. Do you think this is much better than the 190 degree superposition on the same exhaust systemExhaust wave superposition occurs when an exhaust port opens, not when it closes, so superposition does not directly enhance the reflected pulse from an expansion chamber; it enhances the primary pulse that is entering the expansion chamber. And yes, this enhanced primary pulse will lead to a stronger reflected pulse. In a good engine this reflected pulse may have an amplitude of about 2,5 bar.

Now let's look at Y-manifolds and how we can use the exhaust pulse that exits the exhaust port of one cylinder to directly supercharge the neighbour cylinder.
I call this phenomenon cross-charging, and it requires that the primary pulse out of a cylinder that opens its exhaust port, arrives at the other cylinder before this closes its exhaust port. This obviously requires an exhaust timing of over 180°, and because the pulse has to travel via the Y-manifold, we have to allow for some travel time as well. Finally, we want to give the pulse sufficient time to inflict its maximum amplitude on the second cylinder. All in all, the required exhaust timing for effective cross-charging will be in the region of 220°.

An exhaust port this high will reduce the working stroke of the piston to just 70°. Is that bad? For this working stroke: yes. But just look at what we get in return.
The opening pressure of an exhaust port with a normal 202° timing (normal for an Aprilia RSA, that is) will be just below 12 bar. But the opening pressure of an exhaust port with a 220° timing will be close to 20 bar! Now that is some supercharging, compared to the 2,5 bar of a reflected pipe pulse.

The icing on the cake would be a rotary drum in the Y-manifold, momentarily closing the manifold exit when an exhaust port opens, so that the total pulse energy exiting that exhaust port has nowhere to go but to the other exhaust port.

Detail questions: how short should the manifold be? Not too short, because it should be able to hold all the mixture that will subsequently be shoved into the neighbour cylinder.
What about intercooling? There wil be hardly any place for an intercooler, and supercharging a cylinder with high-pressure hot mixture is begging for detonation, so maybe we should scavenge with pure air instead of mixture. And that would require direct injection. Diesel and HCCI come to mind...

[breezy]

quote.
"An exhaust port this high will reduce the working stroke of the piston to just 70°. Is that bad? For this working stroke: yes. But just look at what we get in return.
The opening pressure of an exhaust port with a normal 202° timing (normal for an Aprilia RSA, that is) will be just below 12 bar. But the opening pressure of an exhaust port with a 220° timing will be close to 20 bar! Now that is some supercharging, compared to the 2,5 bar of a reflected pipe pulse."



wow thats an interesting fact... 20 bar!.... heat causing detonation being the downside....when maybe used as a plugging source.

[wax]

That is what Jan Thiel would prefer now, based on his experience with the rear-disc-valve RSA.

Exhaust wave superposition occurs when an exhaust port opens, not when it closes, so superposition does not directly enhance the reflected pulse from an expansion chamber; it enhances the primary pulse that is entering the expansion chamber. And yes, this enhanced primary pulse will lead to a stronger reflected pulse. In a good engine this reflected pulse may have an amplitude of about 2,5 bar.

Now let's look at Y-manifolds and how we can use the exhaust pulse that exits the exhaust port of one cylinder to directly supercharge the neighbour cylinder.
I call this phenomenon cross-charging, and it requires that the primary pulse out of a cylinder that opens its exhaust port, arrives at the other cylinder before this closes its exhaust port. This obviously requires an exhaust timing of over 180°, and because the pulse has to travel via the Y-manifold, we have to allow for some travel time as well. Finally, we want to give the pulse sufficient time to inflict its maximum amplitude on the second cylinder. All in all, the required exhaust timing for effective cross-charging will be in the region of 220°.

An exhaust port this high will reduce the working stroke of the piston to just 70°. Is that bad? For this working stroke: yes. But just look at what we get in return.
The opening pressure of an exhaust port with a normal 202° timing (normal for an Aprilia RSA, that is) will be just below 12 bar. But the opening pressure of an exhaust port with a 220° timing will be close to 20 bar! Now that is some supercharging, compared to the 2,5 bar of a reflected pipe pulse.

The icing on the cake would be a rotary drum in the Y-manifold, momentarily closing the manifold exit when an exhaust port opens, so that the total pulse energy exiting that exhaust port has nowhere to go but to the other exhaust port.

Detail questions: how short should the manifold be? Not too short, because it should be able to hold all the mixture that will subsequently be shoved into the neighbour cylinder.
What about intercooling? There wil be hardly any place for an intercooler, and supercharging a cylinder with high-pressure hot mixture is begging for detonation, so maybe we should scavenge with pure air instead of mixture. And that would require direct injection. Diesel and HCCI come to mind...
Wow thats an awesome answer thank you.
I have never even considered going that high with an exhaust port. I have a few cylinders I can try this with. I will do this and see what happens. Im guessing I will have a heap of blow down time

[wobbly]

What would be considered " normal " in a twin cylinder with a single pipe ( as simply by using a single you are by defenition creating low bmep )
the Ex timing will be down at 190 duration.
Crank this up to 202 and the cross charging effect adds more power than it looses due to a reduction in power "stroke ".
Rather than go even higher ( been there done that , moved on ) the next trick is to cut the piston skirts such that there is about 3mm of exposed port at TDC.
This creates havoc with the jetting , but using pumper carbs , they can be tuned way wierd and fix that issue.
In my experements with World Champ open jetski title engines , the "bottom open " port is capable of more power than the other option of going REAL high on the Ex duration.

[wax]

What would be considered " normal " in a twin cylinder with a single pipe ( as simply by using a single you are by defenition creating low bmep )
the Ex timing will be down at 190 duration.
Crank this up to 202 and the cross charging effect adds more power than it looses due to a reduction in power "stroke ".
Rather than go even higher ( been there done that , moved on ) the next trick is to cut the piston skirts such that there is about 3mm of exposed port at TDC.
This creates havoc with the jetting , but using pumper carbs , they can be tuned way wierd and fix that issue.
In my experements with World Champ open jetski title engines , the "bottom open " port is capable of more power than the other option of going REAL high on the Ex duration.
Thanks Wobbly I also read where you wrote that. Im interested to try that and to see how it effects the ski. It seems all wrong but I am not about to second guess you on this one Wobbly. i would love to do a twin pipe engine on the ski I am building but it just seems to be so hard to get these stay together in these hulls.

[wax]

What would be considered " normal " in a twin cylinder with a single pipe ( as simply by using a single you are by defenition creating low bmep )
the Ex timing will be down at 190 duration.
Crank this up to 202 and the cross charging effect adds more power than it looses due to a reduction in power "stroke ".
Rather than go even higher ( been there done that , moved on ) the next trick is to cut the piston skirts such that there is about 3mm of exposed port at TDC.
This creates havoc with the jetting , but using pumper carbs , they can be tuned way wierd and fix that issue.
In my experements with World Champ open jetski title engines , the "bottom open " port is capable of more power than the other option of going REAL high on the Ex duration.

Does the flow come from the crank case or go back into it . It would seem that the pressure in the exhaust is higher than the pressure in the crank case and thus flows into the crankcase, please help me with this one

[wobbly]

The pressure traces show that in a single cylinder at TDC the reeds are already starting to close , as the case pressure has already started to rise above atmospheric.
Thus I make the asumption that the big negative pressure ratio around BDC of the other 180* out of phase cylinder , also arrives at the open bottom port , sucks like the old chrome off a towball joke
and delays the case pressure rise .

Therefore this big negative pressure ratio sucking on the partially open port holds the reeds open longer - giving rise to an increase in Delivery Ratio.
Of all the inherent variables such as Scavenging and Trapping Efficiency , the simple act of filling the case with more A/F mixture with a " cheat " like this has a big effect on the Delivery Ratio - the hardest
I believe to influence dramatically by what we consider normal tuning.

[TZ350]

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[wax]

The pressure traces show that in a single cylinder at TDC the reeds are already starting to close , as the case pressure has already started to rise above atmospheric.
Thus I make the asumption that the big negative pressure ratio around BDC of the other 180* out of phase cylinder , also arrives at the open bottom port , sucks like the old chrome off a towball joke
and delays the case pressure rise .

Therefore this big negative pressure ratio sucking on the partially open port holds the reeds open longer - giving rise to an increase in Delivery Ratio.
Of all the inherent variables such as Scavenging and Trapping Efficiency , the simple act of filling the case with more A/F mixture with a " cheat " like this has a big effect on the Delivery Ratio - the hardest
I believe to influence dramatically by what we consider normal tuning.
Thanks
yeah it kinda makes sense. im interested to know if you found it by accident or you actually decided to try it. Its a cool thing anyway. I cant imagine its good for economy but then I dont care lol . Greta hates me

[Haufen]

Making the reed cavity exit area into the case , smaller and smaller has been a trend over the last several years.

Do you happen to have a rule of thumb regarding this? For example xy% of the effective reed petal opening area or something like this?
I am thinking about adding the possibility to fit stuffers of variable sizes to my next project or the one after that.

Is it really beneficial to make the exit into the case this small (Vortex DJT)?
347576

[philou]

Would be an exhaust of the latest aprilia rsa.
It seems improbable to me

347577

[Frits Overmars]

Would be an exhaust of the latest aprilia rsa.
It seems improbable to me
347577You're right Philou. Below you'll find the Aprilia RSA pipe, codename Tubo102, once more.
The pipe in your above drawing is probably an early Rotax pipe, maybe model VSK150 or thereabouts, from before 1990, or a derivative thereof.
The partly visible logo on the right of your drawing belongs to Gazzaniga, an Italian producer of underwear who ran a 125cc GP racing team around 1990 with my friend Dolph van der Woude as designer/constructor. Dolph can probably tell us more about your drawing if he happens to drop in.
347579347578

[wobbly]

Some of the pipes done at Rotax in the early days of the 256 and 128 had some quite different designs, alot of which I had never seen before.
Yes I think that is VSK 150 - I always wondered what VSK represented , or who actually did the new designs at Rotax back then.
This pipe if I remember correctly we used as a basis at JL, when trying to get the same power out of fully blown manufacture , except the first thing I changed was to a single rear cone.
We were sick of making the 180* U turn for the front pipe on the Tandem twin for Superkarts .
Making that part front U part blown worked, but we could never get equal power by doing the rest .Hand made cones were always better.

[wax]

The pressure traces show that in a single cylinder at TDC the reeds are already starting to close , as the case pressure has already started to rise above atmospheric.
Thus I make the asumption that the big negative pressure ratio around BDC of the other 180* out of phase cylinder , also arrives at the open bottom port , sucks like the old chrome off a towball joke
and delays the case pressure rise .

Therefore this big negative pressure ratio sucking on the partially open port holds the reeds open longer - giving rise to an increase in Delivery Ratio.
Of all the inherent variables such as Scavenging and Trapping Efficiency , the simple act of filling the case with more A/F mixture with a " cheat " like this has a big effect on the Delivery Ratio - the hardest
I believe to influence dramatically by what we consider normal tuning.

Im guessing this would be even better on a case reed due to have the carb right there aimed at it

[wax]

Ok well if i can ask you guys to look over this
I have a 550 cc engine I am racing in the vintage class at the world finials
Im trying to get to the best power i can of course and here is it put through enginemod
The issue I have is trying to get the exhaust port to make the power
I have loaded two sta up here one is at the exhaust port at 75% and one at 70%. I just dont know that the the engine will live at 75% its really not going to go much over about 7700-8000 rpm
I would really appreciate your thoughts

[Frits Overmars]

The issue I have is trying to get the exhaust port to make the power
I have loaded two sta up here one is at the exhaust port at 75% and one at 70%. I just dont know that the engine will live at 75% From looking at your port drawing, without dimensions, it is hard to tell whether the engine will live. But anyway, an exhaust port with a shape that is safe for the piston ring and with a width of 75% of the bore, will give less, not more, blowdown time.area than a 70%-wide safe port.
A 75%-wide port requires bigger corner radii to keep the piston ring alive, which reduces the uppermost parts of the blowdown area (the yellow areas in the left-hand drawing) that are the most important because they are open for the longest time.
The right-hand drawing can help you establish the safe shape for any exhaust port, assuming good quality steel piston rings.
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