ESE's works engine tuner

[lohring]

We run nitro on glow ignition race engines. It really helps the smaller engines (2.5 cc) where 66% nitro is common. I ran 60% nitro on all my engines, but the consensus for engines over 10cc was 50% is plenty. We did some limited testing on 26cc ignition engines. They ran fine on 15% nitro standard fuel, but burned the electrodes off the plug, denting the piston on the way out, on 40% nitro. We did a series of fuel tests on a 26 cc engine setup for gasoline. We only changed the needle settings to best power for the various fuel mixtures. All this convinced me that fuel cheating in our racing wouldn't matter and extensive fuel testing like that used in larger racing classes wouldn't be needed. See the test results below.

Lohring Miller

354971

[TZ350]

So could a switched PJ be used to add the nitro at the desired RPMs?
I could see adjusting timing to coincide with the nitro but compression would be a bit beyond me.

Suitable compression plus switched PJ and Ignition map is the plan if I ever go there. A thumb trigger button, digital ignition and peristaltic pump.

354972

Remember, With a properly jetted carb for petrol you don't have to enrich it if you are just squirting raw Nitro into the inlet tract. The added Nitro brings its own fuel in the correct (actually slightly rich) proportion with it.

[diesel pig]

What amazes is the dyno traces of TZ350 50cc on Avgas and Avgas + nitro apart from the Avgas + nitro coming in a thousand rev's earlier they match each other curve for curve up to full power. Which I think would point to much more power with the carburation and ignition sorted all out to suit the nitro.

[adegnes]

Suitable compression plus switched PJ and Ignition map is the plan if I ever go there. A thumb trigger button, digital ignition and peristaltic pump.

354972

Remember, With a properly jetted carb for petrol you don't have to enrich it if you are just squirting raw Nitro into the inlet tract. The added Nitro brings its own fuel in the correct (actually slightly rich) proportion with it.

When you did the squirt bottle testing, why do you think it acted too rich at higher rpm? Not enough timing? Too large fuel droplets not contributing to combustion?

I may or may not have snuck some pure nitro across the border from Sweden, not allowed in Norway.
Setting up a Derbi GPR50 as a test bench for nitromethane injection alongside normal carb on gas, and also continuos methanol/nitro injection.

For nitromethane injection I will try a 0.9mm water-injection nozzle + high pressure efi pump. Might need a smaller nozzle.

[adegnes]

What amazes is the dyno traces of TZ350 50cc on Avgas and Avgas + nitro apart from the Avgas + nitro coming in a thousand rev's earlier they match each other curve for curve up to full power. Which I think would point to much more power with the carburation and ignition sorted all out to suit the nitro.

If one can make it work in a two stroke, power should pretty much only be limited by how much properly atomized fuel you can manage to shove in there and still have combustion. If combustion doesn't hapoen it hydro locks and grenades.

As the fuel class at Bonneville is unlimited(before you suggest Flourine/Lithium/Hydrogen, within reason.), effort into making nitro work is worthwhile.

As stated before, experimental stuff will be kept away from the main engine until it's no longer experimental stuff. No free jazz.

[F5 Dave]

So how can the dyno trace slope backwards? Is the sw getting creative? I've dynod quite a few engines and never seen that.

[adegnes]

So how can the dyno trace slope backwards? Is the sw getting creative? I've dynod quite a few engines and never seen that.

Two different power measurements for same rpm points i suppose. Maybe rolled off throttle a little slow.
If you run up and down in revs a few times during a run and plot hp vs rpm you get loops and stuff. With practice you could probably draw a nice picture.

[TZ350]

.

When you did the squirt bottle testing, why do you think it acted too rich at higher rpm? Not enough timing? Too large fuel droplets not contributing to combustion? For nitromethane injection I will try a 0.9mm water-injection nozzle + high pressure efi pump. Might need a smaller nozzle.

354974 RG50 Petrol Carb plus a squirt of Nitro runs.

This engine was tuned for petrol. It seemed to me, that with the added squirt of Nitro, the engine became distressed when it got near maximum torque. I concluded the ignition and or compression was suboptimal for added Nitro. I wasn't going to change anything because this Nitro thing was just for shits and giggles and maybe future reference.

I started shutting off early on runs that had more Nitro. The test was to prove that Nitro squirted into the inlet on a properly carbureted engine on petrol would run without blowing up. Clearly my engine would need some ignition/compression adjustment to be able to use Nitro at maximum power but the basic idea worked on the dyno.

I just used a squirt bottle that squirted a raw liquid stream of Nitro into the carburetors' throat. The first runs were done with a careful squirt, the last (Red Line) was pretty heavy handed.

Could you squirt in enough Nitro so that the surplus fuel that comes with the Nitro itself made the engine over rich, possibly but I don't think that was happening to me.

Given proper ignition and compression, I don't think there are any real limits to the amount of Nitro you can use other than wetting the plug, hydraulic locking or over stressed mechanical breakage.

A pump with an atomising injection nozzle sounds like a good idea. Being able to turn the Nitro on/off as required is a great idea too.

[F5 Dave]

While we are on weird dyno curves, my early attempt to tune the H100 onda with an MX type power decades ago I designed a pipe using TSR software. It was quite fat and the curve had about 3 peaks. Chris's dyno, he teased me making Rooster head shape with his hand on his head.

I assumed that the pipe was just too fat for the transfers, but any ideas?
I kinda smoothed it out a bit and made a boost bottle to that aim, it was only the spare bike for a bit of fun.

[adegnes]

I always find it funny when I manage to get negative power in simulations.
Also, when testing a centrifugal blower on my 50 I got to a point where it would rev to pretty high rpm and just stay there, dyno reading 0hp. That's efficiency for you, 0%. Blower was in constant surge.

[husaberg]

2 stroke music

https://www.youtube.com/watch?v=OY8zDhLk_S0

[adegnes]

High pressure gear pump for my electromechanical fuel injection system arrived from china.

354982

Ignitech Dccdip1/2race has input for TPS, and can output PWM.
Looks like I'm stuck with four throttle position points, and five rpm points which is restrictive, but might be enough when WOT at pretty much constant load is all that matters anyway.
I'm assuming there's interpolation between these points, can anyone confirm?

354981

You see where I'm going with this?
No RAD compensation, if only the Ignitech could accept TPS and some other sensor simultaneously.
Easy enough to shift the whole map according to conditions, or even have the pwm signal pass through an Arduino that modifies it based on RAD.

[JanBros]

I wonder how long those hydraulic pumps will last without oil to lubricate them

[adegnes]

I wonder how long those hydraulic pumps will last without oil to lubricate them

I'm hoping 5-10% oil will be sufficient to keep it happy.

I just realized RC ESCs for brushless motors want special servo PWM, they care about the width of the pulse, not on/off time.
Is this special servo PWM what comes out of the ignitech "servo" output?
If so we just got a much higher resolution fuel map.
Regardless of what it outputs it should be possible to use that signal and convert it through an Arduino.

Edit: Is the servo output like: Send power to one wire until there's this set voltage on another wire? That's annoying.

354983

[wobbly]

Yes the processor interpolates between data points.
Talk to Jiri at Ignitech he does the programming.
You will have to do the dyno " best power egt " , then learn and construct a Density Altitude/Jet size graph manually first, to then be able to use the data for auto compensation , no matter how you do it.

EDIT , yea the servo uses the position 0-5V output and continuously tries to correct the as read number to equal the table number - within the hysteresis allowance.
And to use two sensors to manipulate an output you would need a 3D table

[adegnes]

Thanks Wobbly! I'll contact ignitech, maybe I can persuade them to add more map points to the pwm output.

[Wos]

Yes the processor interpolates between data points.


Is ignition table also interpolated?

Thanks a lot!! 😉

Grüße Wolfgang

[wobbly]

Yes. And a point to note is the PV seems to work better/faster with the least number of set points along the curve.

[palezu]

Update of my high power 50cc sewing machine MB40 transfer cylinder project. It seems I have finally cracked it and of course it was the simplest thing of all, exhaust porting. I went and hogged the auxiliary ports to double the size that they were before and thinned out the bridges. The thing got a huge boost and now the best number is 15.3 rear wheel hp at 13800 with no precise tuning. Probably has close to 10nm of crankshaft torque which is amazing. Exhaust timing is about 198 and aux ports are maybe only 3 degrees lower. I also tried the much discussed 1.3 case compression and found that it lost power significantly, about 1hp everywhere. When I removed case stuffing the power went directly back up where it was. Currently the engine has only a 1.19 case compression ratio (Minarelli AM6 cases).

It seems that Frits MB40 transfers, without the legendary B duct hook, can work just as well as a normal duct setup. I even have a huge 12mm adapter plate for the cylinder mounting which makes the transfers that much shorter so the transfer geometry is a lot different than normal. I am sure there is more in it because now there is some errors in the port heights, A port is lower than piston edge at BDC and I also have a stock-size AM6 vforce reed valve which I believe is restricting flow somewhat. Exhaust outlet area is roughly 28mm equivalent and the pipe starts with that diameter. I have not calculated outlet/cylinder port area ratio. Previously I said that the 75% rule probably doesn't work in a 50cc but now I see that if you make the cylinder ports freaking huge, then it starts to make more sense. I'm guessing the outlet area is somewhere between 85-90% now.

[wobbly]

Several points to make clear - any change in CCR will require a change in petal thickness to optimize it. Big cases will work fine with a reed as long as the 1st Mode frequency of the
petals matches the Helmholtz of the case. But it has been found that as a general rule a big case down at 1.2 needs reeds that are too thin , and they go spastic at high rpm.
The 1.3 general guide seems to need petals that give the desired power, and also retain control when pushing peak power rpm to the mechanical limit.
In a 50 cc - 13800 rpm is not even remotely close to the mechanical limit - go to 17,000 and things will be very , very different - as would the possible power potential.

The current 125 KZ engines make peak at that same rpm, and with say near 17 crank Hp at that 13800 rpm, the 50cc is only pushing 11.16 Bar bmep , so isnt even warmed up yet.
If you simply made a smaller case in isolation and didnt try changing the petals , then there is very likely unseen power left on the table.

The B hook cannot and does not " work " in isolation. If the radial and axial angles of the other transfers do not conform in general to the Frits/Aprilia scavenging pattern ie the staged
decreasing axial angle of A & B and the radial wall angles meeting at about 1/3 distance from the boost face to bore center ,the B hook wont be effective as it works in synergy with those
other elements to create the Leaning Tower column up the back wall, plus it clears out more Exhaust residuals in front of the boost port.

And if the duct exit, after making a big increase in Blowdown, is now approaching 85% , then it was miles too big to start with , and needs reducing even more to be anywhere near optimal.
Using the 75% guide with 100% at the header entry gives a steep ( 10* -14*) of diffuser slip joint transition right at the duct exit , and this instantly gives a huge boost in peak and overev power
when approaching 0.8 Mach at the restriction point.
You can choose to use that ,as is, or lengthen the pipe and get more power everywhere.

[Flettner]

What percentage exhaust on this one?
Treat it like two single port 65cc?

[wobbly]

Determine the chordal area of the port at the bore face x Cosine of the roof down angle x 0.75/2 = area of each of the two duct exits.
This assumes a T or 3 port setup with shit tons of Blowdown STA.
For a race single port the multiplier is around 0.9 but for those low bmep engines the bulk gas flow is slow compared to a " hot " engine so in this instance I have been down to around 0.8x
to get the exit up near 0.8 Mach .
Still cant believe you have recreated the first 2T that I ever played with - a Jawa twin Exhaust port.

[Flettner]

But with modern transfer arrangement, Nikasil bore and a far more modern pipe (pipes) design.
Next cylinder is water cooled ( even in under the A ports) and twin gate type powervalve.
I haven't seen that before, have you?
Should be intetesting.
170 odd degrees of port rotation around the cylinder with only one bridge. And no port 'wall' in the way at the port extremities.

[wobbly]

Not in any way a criticism of what you have done Neil , in fact the opposite really.
But as a young fella, me ( and everyone else I assume ) I always wondered what Jawa were trying to achieve, as to my knowledge its not been done again since.
You have very good logical reasoning behind the idea , best of luck with the development.

[Grumph]

Not in any way a criticism of what you have done Neil , in fact the opposite really.
But as a young fella, me ( and everyone else I assume ) I always wondered what Jawa were trying to achieve, as to my knowledge its not been done again since.
You have very good logical reasoning behind the idea , best of luck with the development.

According to Irving, it was to avoid a single concentration of heat source. But he also points out the badly cooled area between the ports.

I liked riding the twin-port motocrossers. A couple of friends had them and I'd borrow one for "visitors races". Which are now a thing of the past.

[pete376403]

According to Irving, it was to avoid a single concentration of heat source. But he also points out the badly cooled area between the ports.

I liked riding the twin-port motocrossers. A couple of friends had them and I'd borrow one for "visitors races". Which are now a thing of the past.

Could it be anything to do with exhaust volume, ie two slim expansion chambers giving more ground clearance (useful in MX) than one big fat pipe? I recall the CZ pipes were always underneath, while the Japanese bikes used a single high pipe

[Grumph]

Could it be anything to do with exhaust volume, ie two slim expansion chambers giving more ground clearance (useful in MX) than one big fat pipe? I recall the CZ pipes were always underneath, while the Japanese bikes used a single high pipe

The twin port pipes were always heavily dented. Memory says a mate blew the dents out twice a season.

[F5 Dave]

Could it be anything to do with exhaust volume, ie two slim expansion chambers giving more ground clearance (useful in MX) than one big fat pipe? I recall the CZ pipes were always underneath, while the Japanese bikes used a single high pipe
The TMs etc had low pipe., I bet someone got excited as the first high pipes were seen, and the collective race teams face palmed then fired up their welders, while the production factories were trying to hope the problem away for a few years.

[Flettner]

Who knows?
But at least I can give it a go, lets see what happens.

[husaberg]

Not in any way a criticism of what you have done Neil , in fact the opposite really.
But as a young fella, me ( and everyone else I assume ) I always wondered what Jawa were trying to achieve, as to my knowledge its not been done again since.
You have very good logical reasoning behind the idea , best of luck with the development.


According to Irving, it was to avoid a single concentration of heat source. But he also points out the badly cooled area between the ports.

I liked riding the twin-port motocrossers. A couple of friends had them and I'd borrow one for "visitors races". Which are now a thing of the past.

i assumed the same as Greg plus the ring tech plus the piston tech might not have allowed wide ports.

Geeves was also a twin port 360n and 380 they also like a single down tube which may have been a factor only the larger models had the twin ports.


1920's Villiers had twin ports (plus autolube) and water or air cooling
I think Blair of QUB might have had a hand in the design or maybe just its redesign of the large greeves and I think their large bore QUB500 air cooled single might have also been twin port (at least one model)

[jbiplane]

Hi folks. I saw somitimes on pictures here 3 cylinder engines where 2 cylinders oriented to the top and medium cylinder to bottom.
How looks crankshaft for this engines? Angles, firing order?

[Frits Overmars]

Hi folks. I saw somitimes on pictures here 3 cylinder engines where 2 cylinders oriented to the top and medium cylinder to bottom. How looks crankshaft for this engines? Angles, firing order?Here you go Valery.
354998354997354996

[jbiplane]

Here you go Valery
Thanks you very much Frits! You are real 2-stroke wikipedia :)
Why they move second crankpin position by 8 degree? Cylinders count from front to back and angle cylinder to cylinder 120 and 0 degree?
I saw Honda MVX250F crank in internet. They make a dit different wayhttps://www.mcnews.com.au/wp-content/uploads/2015/05/Honda-MVX250F-Crankshaft-Rods-1024x935.jpg

Below Soviet engine from 1960
3x116cc bore 54 stroke 52
https://roker.kiev.ua/techinfo/rare/dvigatel/trekhcilindrovyjj-dvukhtaktnyjj/dvigatel-so-snyatym-levym-cilindrom.jpg
Cylinder to cylinder angle is 55 degree. On crankshaft second pin ofsetted 65 degree, third 120

By the way I saw here drawings of JBB V90 crankshaft.
I estimating my abilities to make 3cylinder star with 3 individual crakcase chamber.
May be exist picture with a bit better resolution to beter see dimensions. Could be usefull.

[Frits Overmars]

The crankshaft you posted is from the Honda three-cylinder street bike with its outer cylinders firing simultaneously. Note the fat con rod and the massive piston pin in the center cylinder, necessary for balancing.
Below is the JBB V90 crankshaft. I agree it's not very clear but it's the best I have.
354999

[jbiplane]

Great Frits. I proceed your picture with artifical intelect software. Seems now more easy to work with.
https://reaa.ru/attachments/jbb250-v90-crankshaft-jpg.561780/

[Frits Overmars]

That's great too, Valery :niceone:

[wobbly]

When I was designing the BSL500 engine , I supervised a PhD project for one of my engineers to do a balance project for the V3 we had decided upon.

He wrote a code to analyze the probably 50 firing order and phasing/ Vee angle variations I gave him that were physically possible, to optimize both balance forces and rotational inertia.
The final version fired cylinders 1&2 together with cylinder 3 @ 120* later , phased at 120*, and included a balance shaft across 1 & 3.
This was driven of a 1:1 gear pair between 2 cylinders , and drove the clutch off one end and the ignition rotor off the other.

It had zero primary out of balance and was as smooth as a Tesla - much to KR Seniors annoyance when he grabbed the throttle off me in the pit lane
and announced to his team " why cant you dumb fuckers do balance like these guys".

Some time later a gave the App to Jimmy Steadman who had built a Tripple that vibrated your hands off the bars , and he used it with some success in reducing the out of balance with no added shaft to help.
I had the App on an old hard drive - but doubt I could find it.
I will contact Buckley Systems and see if its still on one of the servers.

[Flettner]

According to Irving, it was to avoid a single concentration of heat source. But he also points out the badly cooled area between the ports.

I liked riding the twin-port motocrossers. A couple of friends had them and I'd borrow one for "visitors races". Which are now a thing of the past.

So water cooling would be very desirable, bridge cooled right up to the cylinders edge.
With my AG, it has an unusual power spread, almost two powerbands. Low end is relitively strong up to about 6000 ish, enough to do an entire Vinduro without reving any harder. But from there to 7500 it goes very flat, after that its all on.
I thinking a powervalve will fix this early pipe wave return thats buggering everything up. The high, square exhaust port that spans about 170 degrees of the the cylinder produces a strong wave.
Its a rubbish 58 x 48
195 exhaust, 130 transfers.
No exhaust dam but the next cylinder will have.

[jato]

The crank with #2 displaced 8 degrees i believe is from an RS 500 that had a V angle of 112 degrees - giving the engine an even 120 firing interval. those MVX cranks are configured to (nearly) replicate a 90 degree V twin with the outer cylinders being (nearly again) balanced by the heavy centre cylinder. at one point i weighed all the parts and did some calculations to see it was close to being balanced, but at the cost of the engineering compromises of that heavy centre cylinder

[wobbly]

Yea , the MXV had a HUGE rod and piston mass on the center cylinder - it worked , but effin ugly engineering.
It also had the outer cylinders out of phase slightly , I thought so the the primary drive wasnt stressed on the same one pair of gear teeth, each revolution.
Honda has had some super clever dudes who seem to know alot more than the average Japanese sewing machine designer graduates , the V5 in Moto GP was absolute genius.

[Grumph]

DKW were there first in the early 50's with a 350/3 noted for it's smooth running.
75degree angle between the upright outers and prone inner cylinders

120 degree firing intervals - initially to suit the mag used at the beginning.

The outer crankpins are at 120 degrees to each other.
The middle pin is 45 degrees out of phase with the right hand side pin.

[husaberg]

355005355001355002355003355004355006
Compares the MVX the NS500 and the DKW

[jato]

I guess the DKW has relatively small forces at play with 115 cc a cylinder, but it surprises me it was smooth. the 750 V3 was originally assembled with a 120 degree firing interval (no balance shaft) and while it sounded nice and went really well, as wobbly mentions the vibrations were wild, with the top triple clamp becoming a blur beyond 8 or 9 000 rpm. from memory each crankpin was transferring 12000 newtons of force at full revs. the crank was then re-arranged to have the primary forces at 120 degree and it became somewhat raceworthy with quite a decent rocking couple across the engine. during design provision was made for a partial length balance shaft (from #1 to between #2 and #3) so next that was installed and it improved things more but the lesson is that size V3 engine really needs a full length balance shaft.

[Grumph]

Vic Willougby describes the DKW as "turbine smooth" when he rode it.

He was told it was safe to 15000rpm - but peak power was 10500rpm.

[Flettner]

Wobbly, estimate, at 55 stroke would you give a 3mm exhaust dam? Or less?

[jbiplane]

I estimating if it is rational make 3 cylinder star of cylinder I have. It should be alternate to Koenig SC430
I make 3d assembly of crankshaft in 3d CAD and play with crank geometry to reach the best balance.
Planned use Yamaha DT175 connecting rod with center to center 100mm, bottom hole 28mm, upper hole 20mm

This assembly fluctuate centre of gravity about 0.14mm
https://reaa.ru/attachments/balance-star-png.561833/

But crankshaft with common 22x80 mm pin looks a bit fragile and may be I change intent to 4 cylinder V90.
https://reaa.ru/attachments/crank-for-star-png.561834/

If I will make 4 cylinder V90 I want simplest possible intake with one manifold and one drum valve in the centre of the engine.
Dont want reed valve which badly behave at -40C in Siberia.

[F5 Dave]

Why would you be doing anything in those conditions? This doesn't sound like leisure activities.

[wobbly]

Flett, as I have stated several times, there has to date only been two actual dyno confirmations to my knowledge that the 3mm floor lift on a 54.5 stroke
actually works.
Jan did it on the last RSA , he made one higher , but then retired and had that recut back to 3mm.
I did it on a TM homologation test engine and that worked as well - but it was kept as a" factory special " mod only.
There are two issues at play that make things difficult.
One is that Jan stated the mod only worked at all , when the Blowdown had been fully optimized ie the Aux around to bore center and made as high as possible
before loosing power band width.
The second issue is that its easy to say - make the dam higher then grind it down if its too high , but the ground bore port edges are only reliable enough for a short dyno test session
and then it has to be replated.

[Flettner]

I got plenty of blow down time / area / flow, like I said exhaust almost round to half way round the cylinder with onlt one bridge and a relatively straight port outlet from each port wndow (water cooled one will be straight) .
I guess its just a shit farm bike moter, apart frim Nikasil cost, I'll leave it at 3mm.
195 - 130 (might actually be closer to 129, shitty castings😁)

[Flettner]

Made a couple of these the other day, I guess a little less now, some actual numbers 😁

[jbiplane]

Anyone know if exist V90 2cylinder or 4cylinder 2-strokes with rotary intake valve?
I saw only ones with piston and reed valve intakes.

JBB250 use rotary valve but a bit exotic way with 2 karbs
https://i69.servimg.com/u/f69/19/14/44/93/img_2613.jpg

[Peter1962]

Anyone know if exist V90 2cylinder or 4cylinder 2-strokes with rotary intake valve?
I saw only ones with piston and reed valve intakes.

JBB250 use rotary valve but a bit exotic way with 2 karbs
https://i69.servimg.com/u/f69/19/14/44/93/img_2613.jpg

There is an enormous amount of info on the JBB saga, the V2 250cc and his other endeavours, at Pitlabe.biz. http://www.pit-lane.biz/t5627p175-oldies-les-motos-jbb-toute-une-histoire.

Go directly to page 8 for the first reactions concerning the V2

Jean-Bertrand Bruneau was a genius.

[Pursang]

Why would you be doing anything in those conditions? This doesn't sound like leisure activities.

Altitude of 4000m with a -15C ground temp.:cold: Flettner could probably advise on the degree of leisure that would be in an Autogyro.

[Flettner]

Altitude of 4000m with a -15C ground temp.:cold: Flettner could probably advise on the degree of leisure that would be in an Autogyro.

Just Autogyroing this weekend, as it happens. 😁

[Peter1962]

Just Autogyroing this weekend, as it happens. ��

Great machines !

Neil, I know that the Butterfly Monarch is no longer available, the company does not exist anymore. But is there a comparable alternative with an as good suspension ? Most gyro's realy have poor suspension...

https://www.google.com/search?client=firefox-b-d&q=butterfly+monarch+gyro#fpstate=ive&vld=cid:b8531944,vid:tjbTZHKn1Uo,st:0

[Flettner]

Great machines !

Neil, I know that the Butterfly Monarch is no longer available, the company does not exist anymore. But is there a comparable alternative with an as good suspension ? Most gyro's realy have poor suspension...

https://www.google.com/search?client=firefox-b-d&q=butterfly+monarch+gyro#fpstate=ive&vld=cid:b8531944,vid:tjbTZHKn1Uo,st:0

The Dominator gyro. Centre line thrust, the best to fly and most stable. Rising rate suspension with shock absobers.
Ive been thankfull of the heavy landing ability several times, while learning to fly.
RFD no longer exits but I do and I still build them (well did)
Im looking at re booting production when I retire in a year and a half or so. Ive decided Ill stick to the single seaters as they are by far the most fun to fly. Especially with a lite powerfull twostroke. 👍

[Flettner]

Great machines !

Neil, I know that the Butterfly Monarch is no longer available, the company does not exist anymore. But is there a comparable alternative with an as good suspension ? Most gyro's realy have poor suspension...

https://www.google.com/search?client=firefox-b-d&q=butterfly+monarch+gyro#fpstate=ive&vld=cid:b8531944,vid:tjbTZHKn1Uo,st:0
Also there are plans around still to build your own.

[jbiplane]

Great machines !
Yes, but here in Siberia we use more safe and practical machines like
https://аэролодка-аллигатор.рф/wp-content/uploads/2024/01/DSC04329-5.jpg
My friend is owner of company which produce such toys and sell a lot each month :)

I have a bit strange question.
Anyone have an experience to connect 2 crankshaft by some type of couplings which allow small misaligment like 0.05mm?
may be Oldham will work for?
https://www.youtube.com/watch?v=utEKKox2WHA

[Grumph]

These work well.

[F5 Dave]

Oil in injectors.

How well do injectors deal with 2 stroke oil?

Er. . I've changed from my beloved carbed HiAce to a Nissan with FI. Diluted but does the old premix gas go through the injectors without clogging them do you think?
Neil/Rob, any issues with large ratio and FI?

[TZ350]

Oil in injectors.

How well do injectors deal with 2 stroke oil? .... does the old premix gas go through the injectors without clogging them ....

My 2 stroke fuel injection ran 20:1 oil mix. No problems with the oil fouling the injectors or my O2 sensor. But not sure what it will do to any catalytic converters or O2 sensors long term.

[TZ350]

.

I have been playing with my rotary valve converted Suzuki RG50's inlet timing. Rotary valve timing was changed and ignition and jetting optimised for each run. Everything else the same.

355021 355022 355023

Red line inlet timing, opens 135 btdc closes 75 atdc. Blue line inlet timing, opens 145 btdc closes 85 atdc. So more is not always better.

[wobbly]

You are dead right TeeZee , but 145 opening is too much for " any " engine , and the results are skewed by the fact that any 50cc race engine making 13Hp at only 12,500 is
not even in the ballpark yet.

[lodgernz]

https://www.youtube.com/watch?v=utEKKox2WHA[/video]

My father's solution to slightly misaligned shafts was a chain pulley on each shaft, with a piece of double-row chain around both. Worked well.

[Grumph]

My father's solution to slightly misaligned shafts was a chain pulley on each shaft, with a piece of double-row chain around both. Worked well.

See my post on the previous page.

This chain on sprockets joiner is traditional in speedway TQ's where a driveshaft comes off the end of a bike motor crankshaft.
Still in use today.

[Flettner]

Yes, but here in Siberia we use more safe and practical machines like
https://аэролодка-аллигатор.рф/wp-content/uploads/2024/01/DSC04329-5.jpg
My friend is owner of company which produce such toys and sell a lot each month :)

I have a bit strange question.
Anyone have an experience to connect 2 crankshaft by some type of couplings which allow small misaligment like 0.05mm?
may be Oldham will work for?
https://www.youtube.com/watch?v=utEKKox2WHA
Practical?

[karter444]

You are dead right TeeZee , but 145 opening is too much for " any " engine , and the results are skewed by the fact that any 50cc race engine making 13Hp at only 12,500 is
not even in the ballpark yet.

Hi Wobbly at what angle BTDC does a reed valve start to open . Im guessing that it depends on rpm and load ??
cheers

[ken seeber]

My 2 stroke fuel injection ran 20:1 oil mix. No problems with the oil fouling the injectors or my O2 sensor. But not sure what it will do to any catalytic converters or O2 sensors long term.

From what I can remember at Orbital, the catalyst, particularly, was affected by 4 stroke engine oils cos they contained both zinc and phosphorous. These are use in the 4T oils because of the EP (extreme pressure) requirement, I guess at the camshaft and followers.

So, from this, 2T oils don't contain the additives and are therefore fine with a catalyst and one could reasonably assume the O2 sensor.

We had no issues in this respect.

[F5 Dave]

Cool. Old premix will go in van. I dont have a lawnmower. Thanks.

[wobbly]

The Lambda O2 sensors are affected by oil ( and we were told - lead ) residues coating the element. We discovered in SKUSA racing with CR125 stock classes
that if it was put into a hollow threaded bung in the very front of the muffler with its tip just short of the perforated , it lasted for years and the readings were very reliable/stable.
Stuck in the belly we had nothing but problems with reliability and inconsistent readings.

Yes , Rotary Valve timing is based around rpm and the STA required to generate the power needed at that rpm.
A few examples I have knowledge of - 300/400/600cc Jetski cylinders running up to 9500 - open 130 to 132 close 65 to 75 depending on the tune , the early Rotax 256 that
made about 40 Hp/cyl at 12200 , open 134 close 86 ( or 88 if tuned higher to 12500 ) and of course the RSA ( plus the modern 250 Superkart clones ) that make 50 - 55 Hp at 13,000
opened between 140 and 142 and closed at 90 to 92 ( depends upon who you believe ).

EDIT - shit I misread the question - in the vast majority of sims I do the reeds do not start to open until the piston is getting close to closing the transfers. This opening point is determined pretty much solely
by how well the intake tract is tuned for the wave action and the column inertia to have max effect around a specific rpm. When the tuned length is perfect , the case pressure ratio goes negative at the same time
as the intake wave , bouncing off atmosphere , arrives back at the reed tips at the same time. This double effect opens the the reeds fast and early, then the column inertia holds them there. The intake tune
works over about a 2000 rpm band , its efficiency is off course subject to the old Pareto principal , 80% of the power is in the pipe , 20% is available to be optimized in the intake system.
To have this work we need the intake in 125 race engines to be pretty much as short as is physically possible , unless the end use is MX where upper mid power is needed . But the issue in bigger 250cc MX is that
it is impossible to get the length correct as the rear suspension is in the way - so they end up with 125 style short angled intakes.
The example shown is a 200cc cylinder at 10,000 rpm. It has a long 40mm Lectron with a big bellmouth extension and a 52 mm long intake manifold. This combines with the end correction plus the reed box length to have the 3rd harmonic
intake effect peaking at the 10,000 rpm shown.

[TZ350]

.
Been having a little issue with my 50 running on after a hard pull and not shutting off when the throttle is closed.

355025 This is what the tip of my Champion G52V 10mm plug looks like new.

355026 What it looks like now.

355027 355028

The heat line on the threads looks to be further down the plug than they should be and it also looks like the spark has been tracking over the porcelain.

Just goes to show how tuff these Suzuki RG50 engines are.

Time to do something about fitting an exhaust gas temperature gauge as an aid to getting the jetting right.

[F5 Dave]

Airleak introduced with new inlet?

[Grumph]

Put the plug in the lathe and take a light cut off the outer ring face.

Enough to remove the plating and expose base metal.

[wobbly]

The porcelain is shattered - hello , Mr Deto is in the house - the center electrode is probably operating like a glow plug.
I have said it a thousand times - if you are not using data to tune - you are playing with yourself in the dark , well I didnt say that but you know what I mean.

[TZ350]

.
355033 Suzuki RG50 with rotary valve conversion.

I was asked if the rotary valve conversion was worth it (Red line), initially I did not think so. But now, with the new timing (Blue line) I am looking forward to riding it Sunday.

Blue line is where I am at now with the RV timing at 135/75. Av Gas.
Red line was my initial RV timing of 145/85. Av Gas.
Brown line was with the original 145/85 Av Gas and a squirt of Nitro. Only on the Dyno of course.
Green Line was with the 145/85 timing and an experimental mix of 25% Methanol + Av Gas. Again, only on the Dyno of course and in the interests of science.

[jbiplane]

The Lambda O2 sensors are affected by oil ( and we were told - lead ) residues coating the element. We discovered in SKUSA racing with CR125 stock classes
that if it was put into a hollow threaded bung in the very front of the muffler with its tip just short of the perforated , it lasted for years and the readings were very reliable/stable.
Stuck in the belly we had nothing but problems with reliability and inconsistent readings.
Do you have any picture how correctly install?

[diesel pig]

What cylinder are you using, TZ350?

[TZ350]

What cylinder are you using, TZ350?

RG50 cylinder with the original inlet tract sealed up with Kneed-It putty. Also for the RV, the left side case was filled up with Kneed-It too before milling it flat for the rotary valve and cover.

355034 355035

[F5 Dave]

Um, have you not made a conventiinal boost port by cutting up to the two rear ports the and blocking the transfers from them?

[wobbly]

Here is the setup for Lambda used on the CR125 in SKUSA

[lodgernz]

RG50 cylinder with the original inlet tract sealed up with Kneed-It putty. Also for the RV, the left side case was filled up with Kneed-It too before milling it flat for the rotary valve and cover.

355034 355035

Rob, did you have to cut the end of the crank to fit the carb directly to that stub?

[TZ350]

Rob, did you have to cut the end of the crank to fit the carb directly to that stub?

Yes. It is also where the ignition trigger gets installed.

355037 355040 355038 355041 355039

This is how I went about it.
I used all the rotary valve parts from a Suzuki GP125 and flywheel.
1) Salvage the crankshaft hub from an old flywheel.
2) Cut the thread off the end of the crankshaft.
3) Drill and tap the crankshaft for a M5 screw.
4) Machine the hub and crank flush. Then machine 0.005" five thou off the end of the crank to give some crush on the hub. You only just want it gently squeezed, just enough to hold it securely but easy to get off again.
5) Make a spacer with about 0.010" ten thou clearance between the hub and the rotary valve driving dog.
6) Insert a 2-3mm thick "O" ring in the face of the spacer to give it some crush on the RV driving dog.
7) The hub is keyed to the crankshaft. Screw a M3 dome head into the hub for the ignition trigger at the appropriate timing position.
8) Crush the dome head in a vice to collapse the Philips star. You need to do this so you don't get two ignition pulses close together. One from each side of the Philips dome head screw.
9) At TDC drill a 5mm hole in the crank shaft for the RV driving dog's driving pin. 5mm fitted the key way in my Suzuki RV driving dog. I cut an old drill bit down to use for the pin.
10) Used a short piece of hose and two hose clips to secure the carburetor to the inlet stub. I put a larger "O" ring inside the hose to prevent metal to metal vibration contact between the carb and stub.

[TZ350]

Um, have you not made a conventional boost port by cutting up to the two rear ports the and blocking the transfers from them?

Yes and no. We did try removing the bridge between the two boost ports. Bad idea. We have not tried the idea you suggest. It looks worth trying. Thanks for the tip.

[diesel pig]

Yes and no. We did try removing the bridge between the two boost ports. Bad idea. We have not tried the idea you suggest. It looks worth trying. Thanks for the tip.

I am fascinated. What made removing the bridge between the two boost or C ports a bad idea? I am thinking about doing something like that to a similar cylinder.

[F5 Dave]

I did this with my RG Reed valve conversion. Many years ago and cocked up as I made a mistake on the exhaust so i abandoned it. Just turned into a convential design. You would extend boost to gasket face (I did this on my case reed MB100 conversion).

[Flettner]

Foundry work, the sides go in last so as to be able to check all is in place.

[Wos]

Dear experts!

Which is minimum bridge of material between main exhaust and the auxiliary ports at a nikasil plated 40mm bore cylinder?

Does the minimum depend on bore size? On shape and cordal width of main?
How wide were the bridges for example in the rsa?

Is there a rule of thump for bridge on a FOS shape 70% cordal main Ex?

thanks a lot ! ;)

Grüße Wolfgang

[wobbly]

3 millimeters

[Wos]

3 millimeters

Hey wobbly,

Thanks for answering 😀
Do you talk from 125 cc...54 bore...rsa? 😀

Is there a corelation to other bores or technical datas? Cant belive 3 mm over all?

Another question to get a feeling what could be minimum bridge at main with auxiliary ports...

What is minimum rlieable coated surface width at a mid bridge on a butterfly ex port?

Tanks from germany to NZ 😉

Grüße Wolfgang

[wobbly]

3mm is needed as a minimum to have sufficient load area supporting the ring face with lubrication.
This works in 125 and smaller cylinders - I have seen a 50cc race cylinder with 2mm Aux bridge widths and it wore away slots in the ring.

[Wos]

3mm is needed as a minimum to have sufficient load area supporting the ring face with lubrication.
This works in 125 and smaller cylinders - I have seen a 50cc race cylinder with 2mm Aux bridge widths and it wore away slots in the ring.

Ouch!!! 😞

Thank you so so much for warning us from wear of the rings!

Its a given buyable tuning cylinder that has around 2 mm bridge that has small main under 65 cordal ...its strong ;) called relieable... ouch!!

My idea was to minimice bridges to get 68 percent because i thaught this is more effective than widen aux!?? Isnt it? 😉
Long therm project...
Tanks for advice...

Have a nice day wobb...got to sleep now here in europe 😉 😀

Thanks for advice

Wolfgang

[wobbly]

In a T port it seems that 2.5mm is the safe minimum , as the chordal width of each side is alot smaller than that of a 70% main.
It is very important to get the T port bridge relief shape and depth correct though when going this thin.

[Wos]

In a T port it seems that 2.5mm is the safe minimum , as the chordal width of each side is alot smaller than that of a 70% main.
It is very important to get the T port bridge relief shape and depth correct though when going this thin.

Wob good morning ;)...Tanks for reading back my edited questions! 😉

In case of butterfly we often have lubrication Support from bores in piston at bridge mid under ring...think.. minding 😉

Do you think, this is possible/ effective at a narrow bridge that devides main from aux to avoid heavy wear of rings to??

Many thanks!!

Wolfgang

[wobbly]

Yes it works , there have been several examples of lubrication holes and slots in pistons over the bridges each side of the boost port - some Aprilia pistons had this.
This is because of the heavy thrust forces from rod angularity.
I have put lube holes each side of the main port ,over the Aux bridges , on a big overbore Banshee based engine , as again the thrust and ring tension was wearing
the piston and bridges badly.

[SwePatrick]

I wonder how long those hydraulic pumps will last without oil to lubricate them

Sadly enough, not to long...
I ran methanol and 6% oil blend through one when i was trying EFI on my bike.
I seized quite fast....

But i ran my pump driven by crankshaft as i had normal efi injectors and fuel pressure regulator.

It seized between the gears and the housing, i expected it to seize at the shafts though, as there were no bearings.
When it seized it grinded off small aluminium parts from the housing, and clogged up the system.

[SwePatrick]

High pressure gear pump for my electromechanical fuel injection system arrived from china.

354982

Ignitech Dccdip1/2race has input for TPS, and can output PWM.
Looks like I'm stuck with four throttle position points, and five rpm points which is restrictive, but might be enough when WOT at pretty much constant load is all that matters anyway.
I'm assuming there's interpolation between these points, can anyone confirm?

354981

You see where I'm going with this?
No RAD compensation, if only the Ignitech could accept TPS and some other sensor simultaneously.
Easy enough to shift the whole map according to conditions, or even have the pwm signal pass through an Arduino that modifies it based on RAD.

How do you compensate for increased demand of fuel when 'the heat comes'?
My experiance is that when nitro burns hot, you need to 'put out the fire' with more fuel.....
Not doing so often results in damage.

And you cant run 'this' amount of fuel from the start, as it will 'drown' the engine, and it will never come up on the pipe.

[Wos]

Yes it works , there have been several examples of lubrication holes and slots in pistons over the bridges each side of the boost port - some Aprilia pistons had this.
This is because of the heavy thrust forces from rod angularity.
I have put lube holes each side of the main port ,over the Aux bridges , on a big overbore Banshee based engine , as again the thrust and ring tension was wearing
the piston and bridges badly.

Hey wobbly thanks!

I think the bigger the mass of piston the the bigger the forces and the bigger bore the bigger tilt of piston !?
And the power you gain..the load on piston crown...

Which would be the best solution to help narrow bridges wobb?

Like in picture where bores going thru piston?

Thanks so much ;)

[jbiplane]

https://youtube.com/shorts/KkIgSOC0ypQ?si=Ng4koZ6-MNlCcp3R
A question. What is the best sealing material nowadays for air cooled cylinder head?
I use 0.4mm aluminum and copper sheets, but may be exist other still available variants?

[wobbly]

Yea , here are the bridge lube holes for each side of the boost on a RSA.

Edit , re the head seal on an aircooled - the worst case scenario for this was solved many years ago when we were permitted to run Methanol and thus very high compression.
The copper or alloy gaskets were useless , so I tried two fixes , both worked , but I ended up using both as insurance.
First both surfaces were lapped dead flat on a surface plate , then the first test was to create a " flat labyrinth " seal by machining 3 shallow grooves in the head 2mm wide , 1.5 apart.
This worked just fine with no failures , but I noticed that as the head was not pinned or dowelled in place , when it was reassembled the witness marks on the cylinder were not concentric.
Next was to pin the head and use a single empty groove , then a 2mm Viton O Ring outside that. The groove depth was 10% less than the diameter and the width was 20% wider with the OD matching.
This also worked perfectly and was used later with a petrol head , so excess temp on the O ring proved not to be an issue.

[Wos]

Yea , here are the bridge lube holes for each side of the boost on a RSA.

Wobb...are you sure?

From my view that are bores for lubrication c to b ports 😉 bridges ...hmm 😉

But good to know even that was done:shit: wow 😉

Frits or Jan told us never!? 😉

[wobbly]

Well the holes are directly over the bridges each side of the boost port - not sure what the slot actually does , but the picture was published ages ago by Frits.
If you look closely you can see the boost bridges have left witness marks on the piston skirt, directly over the holes.
Here is another one showing Frits Torlon piston plug as well.

[Wos]

Well the holes are directly over the bridges each side of the boost port - not sure what the slot actually does , but the picture was published ages ago by Frits.
If you look closely you can see the boost bridges have left witness marks on the piston skirt, directly over the holes.
Here is another one showing Frits Torlon piston plug as well.

Ok wobbly

Maybe the slot is for a kind of ventilation to ducts?...maybe to help oil flow?

Please help us Jan ... Frits 😀 😉

Thanks to all 😉

Grüße Wolfgang

[Pagi]

Wobbly, Frits,

I have a question about port A, B, and C.
Is there a volume relationship between these port and the displacement? If so, what is the distribution between them?

[wobbly]

I think your wording is a bit confusing , as I don't believe " volume " compared to " displacement" are the correct way to look at the elements of tuning you are examining.
The two engines that have had the most development effort put into them , and also have had the rewards gained from that work , are the RSA and the TM KZ.
In essence the only real difference between the two are the KZ's lack of a PV and its idiot straight line mandated ignition.

This gives rise to a differing approach to the scavenging regime and as well as slight differences in the port chordal widths, even though they have the same bore/stroke/displacement.
The RSA had reverse transfer stagger , as this regime favors top end and overev, as well as enabling a higher STA of those ports , due to the total width of the B/C being greater and thus gives extra area
when they are lifted to be the highest.
The KZ has normal stagger and the boost port width is slightly wider , giving a greater powerband width at the expense of peak power.
That is more natural upper mid power and a more powerful overev capability.

Both have the transfers fully occupying as much bore chordal width as is possible within the limits forced by the maximal Exhaust Port width, but both have the STA needed to support the peak power
at their desired rpm.
The RSA made 55Hp at 13,000 and was regularly reved not much past 14,000 , whereas the KZ makes just on 50 Hp at 13800 and is reved to 14800 all day.
The Aprilia regime , including a narrower boost , has been tested in the KZ, and it gained an appreciable amount of peak power , but lost so much in the useable mid ( 10,000 ) rpm
it was way too slow off all the several 2nd gear hairpins.

Thus I believe applying the correct approach to the porting regime , and matching the STA of the Transfers and Blowdown to the required power/rpm define all the ports in a very narrow window.

Thus I dont believe " volume " as such is a useful metric when both engines have the transfers taking up all the available space , and both have the required STA but utilize that area in differing ways to suit the end use.

[Martin1981]

Wobbly, are there any news about the 3XV cylinder TZR 250 engine? Have you dynoed it yet and did it actually make 54hp/cylinder? It would be awesome. Those cylinders were never thought of being that capable.


Talking about that 3XV cylinders you found work so well.....are there any "cheap" "basic" 54.5mm stroke cylinders that good? I can remember once you said the 2004 Honda CR125 is a good cylinder to start with. Are there any other 54.5mm stroke cylinders you know of as good or even better than the 2004 Honda CR 125? Apart from the Aprilia RSA/RSW and the TM KZ cylinders of course.


Thank you for sharing all that knowledge! It is somewhat interesting and exciting.

[wobbly]

The 3XV cylinder with 56 bore can be ported to match the scavenging regime of the RSA , but as it sits on a 50.7 stroke it can never match those similar cylinders for outright power
with a square bore/stroke.
I developed the 3XV in EngMod using every trick in the non existent book ,to be capable of 55 Crank Hp and that will translate to mid 90 RWHP on a DynoJet using Avgas.
The cylinders are almost done and I am waiting for confirmation that the pipe centerlines are correct , as the 3XV and the 3YL/4DP header spigot have very different exit angles.
If that does not happen soon, I can get a 4DP into my workshop in November , apart from the middle week as im going to the OZ Classic titles in Sydney.

The problem with your request for info is that ALL the good cylinders are sat on 54.5mm stroke , not 54.
The Honda 125/250 RS and TM 125MX both have good porting that can be easily modified to give great power - with the caveat that they are all T ports.
I do like the dropping gate PV on the RS and the TM twin slot system.

The KTM is also on 54.5 but has a dumb PV system the opens the Aux ports from the top down - insane, and does not work well no matter how you go about it.
The TM KZ does not have a PV ,and although some insist that isnt needed in drag racing I have seen plenty of evidence to the contrary , but for road racing the PV gives a huge
advantage and much greater options for pipe trickery.

Sadly I cannot think of a 54.5 stroke cylinder with 3 ports where all are closed by the PV like the 3XV.
I have just done a project on a TZM150 for Thailand , and that is a super good cylinder , but I have no idea about a 125 version of that sorry.

[Martin1981]

Thanks, wobbly! Yes, i know. 54,5mm stroke. Not 54. sorry. I will edit my post.

[Niels Abildgaard]

Please enjoy

https://drive.google.com/drive/folders/1ZTQPG-bZZUT7HNBMqT3NqlItJd6AGBuj

[Pagi]

I think your wording is a bit confusing , as I don't believe " volume " compared to " displacement" are the correct way to look at the elements of tuning you are examining.
The two engines that have had the most development effort put into them , and also have had the rewards gained from that work , are the RSA and the TM KZ.
In essence the only real difference between the two are the KZ's lack of a PV and its idiot straight line mandated ignition.

This gives rise to a differing approach to the scavenging regime and as well as slight differences in the port chordal widths, even though they have the same bore/stroke/displacement.
The RSA had reverse transfer stagger , as this regime favors top end and overev, as well as enabling a higher STA of those ports , due to the total width of the B/C being greater and thus gives extra area
when they are lifted to be the highest.
The KZ has normal stagger and the boost port width is slightly wider , giving a greater powerband width at the expense of peak power.
That is more natural upper mid power and a more powerful overev capability.

Both have the transfers fully occupying as much bore chordal width as is possible within the limits forced by the maximal Exhaust Port width, but both have the STA needed to support the peak power
at their desired rpm.
The RSA made 55Hp at 13,000 and was regularly reved not much past 14,000 , whereas the KZ makes just on 50 Hp at 13800 and is reved to 14800 all day.
The Aprilia regime , including a narrower boost , has been tested in the KZ, and it gained an appreciable amount of peak power , but lost so much in the useable mid ( 10,000 ) rpm
it was way too slow off all the several 2nd gear hairpins.

Thus I believe applying the correct approach to the porting regime , and matching the STA of the Transfers and Blowdown to the required power/rpm define all the ports in a very narrow window.

Thus I dont believe " volume " as such is a useful metric when both engines have the transfers taking up all the available space , and both have the required STA but utilize that area in differing ways to suit the end use.

Wobbly,

I seem to have read somewhere on this "ESE's works engine tuner" that most of the gases admitted into the cylinder during the scavenging were in the ports, hence my question, is this true or not? (without taking into account of course the STA and timing which are important), sorry for ma bad english (i use google translate) and Thank you for sharing all that knowledge.

[Niels Abildgaard]

Wobbly, Frits,

I have a question about port A, B, and C.
Is there a volume relationship between these port and the displacement? If so, what is the distribution between them?

The problem is language.
If You had asked :

Is there an optimum area relation between these independent of cylinder size?

the answer is Yes and RSA and KZ got very close thanks to a lot money for try and error .
Max power is proportional to sonic velocity times exhaust blow down area.
If You try to make that bigger by starting blowdown earlier power go down of course and waves in exhaust start misbehaving.
If you make exhaust ports wider, rings are in trouble and scavenge ports get smaller.

To design a maximum power 35ccm cylinder ,You can do Yourself a favour by scaling a Thiel 125ccm RSA cylinder.
That is multiply all RSA linear measures by Third root of 35 divided by 125 that is around 0.6542.
RSA 125 bore was 54mm and new wonderkind thus 35.3mm
The blowdown area goes down with squarerot of 35 divided by 125 that is 0.529.
When crankshaft power of Your 35ccm creation is 0.529times 55 that is 29 horsepower You know that You are in good company.
Same cleverness level as the RSA creators.
By same token a 50ccm should be able to make35 horsepower at crank

[Pagi]

The problem is language.
If You had asked :

Is there an optimum area relation between these independent of cylinder size?

the answer is Yes and RSA and KZ got very close thanks to a lot money for try and error .
Max power is proportional to sonic velocity times exhaust blow down area.
If You try to make that bigger by starting blowdown earlier power go down of course and waves in exhaust start misbehaving.
If you make exhaust ports wider, rings are in trouble and scavenge ports get smaller.

To design a maximum power 35ccm cylinder ,You can do Yourself a favour by scaling a Thiel 125ccm RSA cylinder.
That is multiply all RSA linear measures by Third root of 35 divided by 125 that is around 0.6542.
RSA 125 bore was 54mm and new wonderkind thus 35.3mm
The blowdown area goes down with squarerot of 35 divided by 125 that is 0.529.
When crankshaft power of Your 35ccm creation is 0.529times 55 that is 29 horsepower You know that You are in good company.
Same cleverness level as the RSA creators.
By same token a 50ccm should be able to make35 horsepower at crank

I totally agree with you (STA, timing,...) but my question was really to know if the volume of a port was significant (google translate is bad at translating from French to English...like me!!!!)

[lohring]

The above symposium has some great presentations on opposed piston engines. One of my favorite engines (https://www.youtube.com/watch?v=Mfy05zqn324&t=291s) is being evaluated for military use in new advanced combat vehicles.

Lohring Miller

[wobbly]

Neils , I suggest you check your maths , a 50cc making 35 crank Hp would need a BMEP of 18.65 Bar at 17,000rpm - Im sure I could not make EngMod capable of lying that big,
let alone construct a realistic working sim..

And regarding the duct volume - yes , if you calaculate the actual volume of A/F in all the transfer ducts , it usually exceeds the swept volume of the engine.
Thus any notion of A/F being " drawn " from the case into the cylinder is based on an erroneous assumption.
I just checked the sim for the 3XV cylinders sitting on a 4DP case and those ducts that are quite short and small in entry area are damn near 125cc - so little to no flow from the case occurs when
the transfers are open, unless the VE is well above unity.

[Niels Abildgaard]

Neils , I suggest you check your maths , a 50cc making 35 crank Hp would need a BMEP of 18.65 Bar at 17,000rpm -


If a 54mm stroke thing can do 14800 rpm all day according to You, then a 40 mm stroke thing can do 19980.
And need a BMEP of 13.8 Bar

[wobbly]

You are not comparing apples with apples.

Taking the rpm at peak power ( NOT peak rpm ) the the RSA at 13,000 making 55HP had a bmep of 15.17 Bar and that is a piston speed of 24m/s with a 54.5 stroke.
I think we can all accept that as the benchmark for power and reliability , with " sufficient " overev for road race use.

Taking the 50cc engine , with a 40mm stroke and reving it to 17500 = the same piston speed of 24M/s then that requires a BMEP of 17.8 Bar to make 35 Hp.
Believe me , if I or anyone could achieve 17.8 Bar BMEP , and or achieve 35 Hp in a 50cc ,they would be more famous than Jan Thiel - and I sure as hell aint even close.
I agree, the RSA could be made to overev to 14800 like the KZ does , and the 50cc could also rev to near 20,000 rpm = 27M/s but no one would dream of making peak power at those extreme high piston speeds
as then there would be no chance of achieving any safe overev capability at all.

[JanBros]

And regarding the duct volume - yes , if you calaculate the actual volume of A/F in all the transfer ducts , it usually exceeds the swept volume of the engine.
Thus any notion of A/F being " drawn " from the case into the cylinder is based on an erroneous assumption.
I just checked the sim for the 3XV cylinders sitting on a 4DP case and those ducts that are quite short and small in entry area are damn near 125cc - so little to no flow from the case occurs when
the transfers are open, unless the VE is well above unity.

but to make 50+ BHP from a 125cc, it surely needs more than 125cc's of mixture in the cylinder, no ? after all the cylinder is filled with mixture under presure because of the pipe, just like a turbo overfill's cylinders with more mixture than it's volume ?

[Frank S.]

but to make 50+ BHP from a 125cc, it surely needs more than 125cc's of mixture in the cylinder, no ? after all the cylinder is filled with mixture under presure because of the pipe, just like a turbo overfill's cylinders with more mixture than it's volume ?

When ex closes you have less than half of the volume. And if you have 2 bar of absolut pressure, this equals to 125 cc😁
But you are right with the assumption that more volume is needed because some (or a lot?) gas is drawn into the exhaust

[wobbly]

Well I checked to see if I was talking rubbish , and sadly it seems so. The Aprilia is the only sim I have where the Delivery Ratio is well over unity.
It peaks at around 1.4 , and that means 175 cc per stroke are passing into the cylinder.
The scavenging and trapping efficiency determine how much of the ingested gas in the cylinder is fresh A/F at EPC.
This is the best result I have , all the other sims hover around 1:1, or lower, which is where I got the original logic from.

[husaberg]

Well I checked to see if I was talking rubbish , and sadly it seems so. The Aprilia is the only sim I have where the Delivery Ratio is well over unity.
It peaks at around 1.4 , and that means 175 cc per stroke are passing into the cylinder.
The scavenging and trapping efficiency determine how much of the ingested gas in the cylinder is fresh A/F at EPC.
This is the best result I have , all the other sims hover around 1:1, or lower, which is where I got the original logic from.

Jan or Frits said on vol 1 or 2 of Pitlane that there was (cant remember what but something like 1.7 x the cylinder volume in the transfers. (might have been more 380?)
I could look but both would know what they said and correct what I have got wrong.....

this is not it buggar

Not really. The RSA's TDC crankcase volume is 675 cc (for a 125 cc engine!) but most of this volume is in the transfer ducts. Over the years Honda has produced cylinders with and without the lip that your picture shows, sometimes both types in the same production year. But flow through the C-port is not the most important item of a fast cylinder.
Another point to help you make up your mind: compared to a Honda RS125 or RS250 the Aprilia RSA125 produces about 20% more power per cylinder....

[Storbeck]

I'm trying to understand why the volume of the transfer ports is important.

In order for air to flow OUT of the transfer ports, doesn't an equal volume of air have to flow IN to the transfer ports?

So that the volume of the ports is not so important compared to the resistance to flowing in and out? (and through, and the angles and shapes and such).

[Niels Abildgaard]

I'm trying to understand why the volume of the transfer ports is important.

In order for air to flow OUT of the transfer ports, doesn't an equal volume of air have to flow IN to the transfer ports?

So that the volume of the ports is not so important compared to the resistance to flowing in and out? (and through, and the angles and shapes and such).

Let us talk of transfer port areas and tranfer channels volume and debate will surely fuck up in some other entertaining way.

[wobbly]

Can admin please block the fuckwit posting nothing to do with the subject at hand.

[wobbly]

I think that the relationship between port area and transfer volume isnt something we can discuss with any hope of accuracy as the examples to hand
vary so hugely , but the subject would be a great PhD dissertation paper with a huge amount of comparative testing needed.
But of course that isnt going to happen in todays anti 2T environment.

In my RSA sim the transfer total volume is quite a bit less than the the swept 125cc , and this makes sense as the B port entry is tiny in comparison to even its own A port entry area.
So in this case we have a " small " transfer volume/swept volume relationship , but the highest Delivery Ratio ever seen of 1.4.
The B port area is much greater than that of the A due to the chordal width as well as the higher timing - so we cant draw any definitive conclusions from Jans work.

Many RSA clones used in 250 Superkart racing have the B port entry much larger , as the rear case studs have been moved back - away from the original Rotax pattern Jan had to use.
If this is " better" I do not know in any absolute terms, as the newer generation pipes on those engines probably account for the greater power produced , not the duct configuration in my opinion.

Another example I am working on is the 3XV/4DP on a TZ250. This is making well over 50 Hp in the sim , but it has a short cylinder height and thus short ducts , but the much larger entry areas give almost a 1:1
duct to swept volume ratio , with a DR of close to 1:1.
So in short ,I cant draw any definitive guides from any of this.

Edit - one point of interest was that when I visited Bud Asklands workshop and dyno facility he was working on Raineys new YZR cylinders , they looked almost identical from the bottom as a 3XV
but he had epoxied the A, B , C outer walls with Devcon that was around 5mm thick , when I asked he said the smaller volume made a couple more Hp but that Wayne had remarked that the " throttle connection " feeling
was way better when tested back to back. Being a smartarse I asked was the difference due to case volume - he handed me a case 1/2 with quite large pockets machined above the mains directly next
to the flywheel faces , the answer was " no , it took forever to get the CCR correct so it wasnt changed at all".
Smart man.

[Condyn]

Speaking of devcon Wobbly,
A few months back you were talking about cutting a transfer duct vinamold to fix the rearward leading edge angle by injecting liquid Devcon. I have a cylinder with this same problem and was wondering if you have any results on this test?
And as I am typing this, I remember the strange 2 piece, steep to shallow baffle cone pipe, perhaps on the same project. I am also curious if this has been built and tested on the dyno to verify the sim results. A side note is that I do not doubt the sim, but the oddity still has me wondering. If the project is stalled, I think we all can relate to that. Thank you.

[wobbly]

Making the 3XV B port front wall perpendicular to the bore CL proved to be way easier than I had imagined. The Devcon Liquid B , is very liquid.
So I took the cylinder I cut up to check everything , and simply used a bubble level to get the cylinder 1/2 sitting dead horizontally square , and put some race tape across
the transfer entry at the level I wanted , and using a big plastic syringe I basically kept pouring it in until I could see the liquid creep up to the port edge in the bore.
I left it ovenight to cure , ripped off the tape , and voila ,a perfectly angled and flat duct fill in.
I am going to do the same with the roof of the A port , simply angle the cylinder to 22* and pour in the liquid until it reaches the port edge.
But this will be done after the cylinders are plated.

The " reverse " angled rear cone has been dyno tested in another project , but as a 3 step ,all equal length decreasing contraction.
In the sim the two angle and 3 angle make virtually the same power , but to make 3 shorter rear cones is easier to do in stainless.
I am currently awaiting confirmation that the pipe centerlines actually work on the bike , if the guy doing this fucks around much longer I
have arranged for a 4DP to be delivered to my shop in November , so I can confirm that the laser pattern shapes actually fit.
Its an issue as the pipes are fatter than anything Yamaha put on that series of bikes , and the 3XV has a much steeper duct exit angle than the 3YL/4DP.

EDIT - note that the reverse cone idea only works in this particular situation where everything was done to pump up peak and overev power , the front side being
taken care of due to the fact the 3XV Power Valve closes off all 3 Exhaust ports.
The diffuser geometry was the same - if alot of mid power was needed the last diffuser would be long and steep.

[wobbly]

Here is the reverse rear cone idea used in an overbored TZM150 for short course road racing in Vietnam , again this closes off all 3 Exhaust ports so that easily takes care of the front side power.

[Rudex]

Here is the reverse rear cone idea used in an overbored TZM150 for short course road racing in Vietnam , again this closes off all 3 Exhaust ports so that easily takes care of the front side power.

Wobbly,

The first segment, is the flange?. Why this huge angle before to header?. BTW, I thought header greater than 3.6º it was very high, it is very angled and short.


Another thing. Why the new generation of cylinders in karts or little engines like 2fast, 8.1, malossi, take the parallel wall with the front Aand bottom Bports and the RSA take the B very straight?. If I remember correctly, you posted RSA is for top end power and the parallel separation is for more mid power.

355080

[Condyn]

Thank you for the reply wobbly. I like the liquid epoxy method. It makes it quick and repeatable.

[wobbly]

Mr Rude , the first question re the flange internal angle. This is all covered in the paper I wrote that Neels makes available to EngMod users.
The Exhaust duct exit is sized to create 0.8 Mach velocity ( 0.75 x the port effective chordal area ) at this point , and the header inlet is back to 100% ( or slightly greater ).
This steep angle and the exit velocity starts the diffuser action very early in the the cycle, and gives a huge increase in power around peak and in the overev.
And this can then allow the use of a longer pipe if needed, to generate more front side power.

The header angle and length again dictates the amount of overev generated ( in concert with the 1st diffuser length and angle ) where shorter and steeper again gives peak and overev power
always at the cost of front side.
But in both cases shown all 3 Exhaust ports are closed off by the old ( but very effective ) Yamaha drum PV, that can be servo driven to be fully up only about 1000 rpm from peak
and this gives a huge boost to the front side mechanically , not using pipe the geometry.

Header angle evolved from a very common 3.2* included to then being split 50/50 - 3.5/5.5*, then to a constant 4.5* with the 1st diffuser then being shorter and steeper.
I first used the 4.5* angle on Dr Henise's TZ350 LSR breaking engine - where peak and overev were all important.
But in the latest R2 KZ design we are forced to compromise , by the need to generate more front side power , and use much shallower header angles , but keeping it very short
to then give plenty of overev as well.
All this specific tailoring is super simple to nail down , reliably , using Neels genius code.

The A and B port centerline crossing points are , again , a compromise to generate a wide powerband or simply extra power around peak.
The RSA has a powervalve , so every element of the design could be directed toward creating top end.
Jan did , exactly what I have just done with the 3XV , filled in the B port front wall with epoxy , to make it perpendicular to the bore centerline , and this instantly gave a boost in power around peak.

But the scavenging regime ( including the port stagger geometry ) in say the TM KZ engine ( no PV ) needs a naturally much wider spread of power - again no free lunch, and the peak is suppressed.
Thus we now commonly see differing sets of port heights and wall angles , that are tailored specifically to the end use and the engines mechanical layout dictated by the presence, or lack of a PV.

EDit - the A port front wall in your A ( LH ) version should intersect at the same point as the A and B rear wall - the RSA scavenging pattern.

[jamathi]

Mr Rude , the first question re the flange internal angle. This is all covered in the paper I wrote that Neels makes available to EngMod users.
The Exhaust duct exit is sized to create 0.8 Mach velocity ( 0.75 x the port effective chordal area ) at this point , and the header inlet is back to 100% ( or slightly greater ).
This steep angle and the exit velocity starts the diffuser action very early in the the cycle, and gives a huge increase in power around peak and in the overev.
And this can then allow the use of a longer pipe if needed, to generate more front side power.

The header angle and length again dictates the amount of overev generated ( in concert with the 1st diffuser length and angle ) where shorter and steeper again gives peak and overev power
always at the cost of front side.
But in both cases shown all 3 Exhaust ports are closed off by the old ( but very effective ) Yamaha drum PV, that can be servo driven to be fully up only about 1000 rpm from peak
and this gives a huge boost to the front side mechanically , not using pipe the geometry.

Header angle evolved from a very common 3.2* included to then being split 50/50 - 3.5/5.5*, then to a constant 4.5* with the 1st diffuser then being shorter and steeper.
I first used the 4.5* angle on Dr Henise's TZ350 LSR breaking engine - where peak and overev were all important.
But in the latest R2 KZ design we are forced to compromise , by the need to generate more front side power , and use much shallower header angles , but keeping it very short
to then give plenty of overev as well.
All this specific tailoring is super simple to nail down , reliably , using Neels genius code.

The A and B port centerline crossing points are , again , a compromise to generate a wide powerband or simply extra power around peak.
The RSA has a powervalve , so every element of the design could be directed toward creating top end.
Jan did , exactly what I have just done with the 3XV , filled in the B port front wall with epoxy , to make it perpendicular to the bore centerline , and this instantly gave a boost in power around peak.

But the scavenging regime ( including the port stagger geometry ) in say the TM KZ engine ( no PV ) needs a naturally much wider spread of power - again no free lunch, and the peak is suppressed.
Thus we now commonly see differing sets of port heights and wall angles , that are tailored specifically to the end use and the engines mechanical layout dictated by the presence, or lack of a PV.

EDit - the A port front wall in your A ( LH ) version should intersect at the same point as the A and B rear wall - the RSA scavenging pattern.

The first time I epoxied the B-duct was in 1997, with a very good result, after that all my cylinders were cast that way.
I made my first triple-port exhaust in 1971, may have been the very first to do this...
Far better than a bridged port: More power and a LOT less problems!!!
And you can make a wider A-port...

[Rudex]

Mr Rude , the first question re the flange internal angle. This is all covered in the paper I wrote that Neels makes available to EngMod users.
The Exhaust duct exit is sized to create 0.8 Mach velocity ( 0.75 x the port effective chordal area ) at this point , and the header inlet is back to 100% ( or slightly greater ).
This steep angle and the exit velocity starts the diffuser action very early in the the cycle, and gives a huge increase in power around peak and in the overev.
And this can then allow the use of a longer pipe if needed, to generate more front side power.

The header angle and length again dictates the amount of overev generated ( in concert with the 1st diffuser length and angle ) where shorter and steeper again gives peak and overev power
always at the cost of front side.
But in both cases shown all 3 Exhaust ports are closed off by the old ( but very effective ) Yamaha drum PV, that can be servo driven to be fully up only about 1000 rpm from peak
and this gives a huge boost to the front side mechanically , not using pipe the geometry.

Header angle evolved from a very common 3.2* included to then being split 50/50 - 3.5/5.5*, then to a constant 4.5* with the 1st diffuser then being shorter and steeper.
I first used the 4.5* angle on Dr Henise's TZ350 LSR breaking engine - where peak and overev were all important.
But in the latest R2 KZ design we are forced to compromise , by the need to generate more front side power , and use much shallower header angles , but keeping it very short
to then give plenty of overev as well.
All this specific tailoring is super simple to nail down , reliably , using Neels genius code.

The A and B port centerline crossing points are , again , a compromise to generate a wide powerband or simply extra power around peak.
The RSA has a powervalve , so every element of the design could be directed toward creating top end.
Jan did , exactly what I have just done with the 3XV , filled in the B port front wall with epoxy , to make it perpendicular to the bore centerline , and this instantly gave a boost in power around peak.

But the scavenging regime ( including the port stagger geometry ) in say the TM KZ engine ( no PV ) needs a naturally much wider spread of power - again no free lunch, and the peak is suppressed.
Thus we now commonly see differing sets of port heights and wall angles , that are tailored specifically to the end use and the engines mechanical layout dictated by the presence, or lack of a PV.

EDit - the A port front wall in your A ( LH ) version should intersect at the same point as the A and B rear wall - the RSA scavenging pattern.

Ok, Thanks Wobbly!.

About the layout port. I got it, but what is the current layout on kz-r2 for example?. I mod the picture
355081355082

[wobbly]

I cant give you the exact figures of the R2 as its current homologation and under NDA , but the R1 is very similar with slightly differing timings.
The boost is wider at 32% and both the B walls and A rear cross near to 75% , the A front @ 78%.
I think that the wider boost naturally forces the A & B crossing point further forward , such that their rearward bias does not mask the area directly in front.
Your LH drawing of the RSA the crossing point looks too far forward , its only 18% of bore = 9.7mm , thus the TM is closer to the centerline.
The boost has been run narrower along with the RSA reverse stagger , and it made large power gains above peak , but lost way too much down at 10,000
where it runs off several 2nd gear hairpins during a lap.
The R2 also has a new concept of the smallest CSA of the main Exhaust duct is at around 1/3 length up from the flange face , keeping the original area at the exit.

[diesel pig]

I made my first triple-port exhaust in 1971, may have been the very first to do this...
Far better than a bridged port: More power and a LOT less problems!!!

Jan puts why I hate bridged exhaust ports and love triple-port exhaust, so well, I need say no more on the subject.

[Rudex]

I cant give you the exact figures of the R2 as its current homologation and under NDA , but the R1 is very similar with slightly differing timings.
The boost is wider at 32% and both the B walls and A rear cross near to 75% , the A front @ 78%.
I think that the wider boost naturally forces the A & B crossing point further forward , such that their rearward bias does not mask the area directly in front.
Your LH drawing of the RSA the crossing point looks too far forward , its only 18% of bore = 9.7mm , thus the TM is closer to the centerline.
The boost has been run narrower along with the RSA reverse stagger , and it made large power gains above peak , but lost way too much down at 10,000
where it runs off several 2nd gear hairpins during a lap.
The R2 also has a new concept of the smallest CSA of the main Exhaust duct is at around 1/3 length up from the flange face , keeping the original area at the exit.

Thank you Wobbly,

The picture is from forum i got it to show you grafiically the separation of ports A and B in RSA and style TM cylinders. But I checked it putting in scale 100 and it is ok 82% and 68% rear B, are ok.
I modified the picture to simulate the tm layout. 75% for both A and B rear walls and 78% for front wall A, front B wall is not clear.

With the picture I see visually the diference.

Thank you for your help.355084

[wobbly]

If you widen the boost port on the TM side , and shift the B rear wall over as well , the exit angle would be I believe almost identical to the RSA
but crossing closer to the bore center.
The A rear wall crosses at the same 75% point as the B front and rear. But the A front should be closer to the boost at 78%.
Having each side marked as A and B is confusing things as well, should be RSA and TM.

[JanBros]

Well I checked to see if I was talking rubbish , and sadly it seems so. The Aprilia is the only sim I have where the Delivery Ratio is well over unity.
It peaks at around 1.4 , and that means 175 cc per stroke are passing into the cylinder.

aparently Frits already knew this. just found this in a document of him :

aufgrund der Ansaug- und Abgasresonanzen die pro Kurbelwellenumdrehung angesaugte Luftmenge bei einem Wettbewerbsmotor bis zu 40% größer als der Hubraum sein kann

for the non-german speakers :

because of intake and exhaust resonance, in race-engines the amount of air taken in by the egine each turn of the crankshaft can be up to 40% more than it's cylinder volume

[wobbly]

That 1.4 DR is from the RSA - still blows every other race engine out of the water.
Apart from a couple of 250 Superkart , very much clone cylinders , but with later , more developed pipe geometry.
As you would expect.

[jamathi]

That 1.4 DR is from the RSA - still blows every other race engine out of the water.
Apart from a couple of 250 Superkart , very much clone cylinders , but with later , more developed pipe geometry.
As you would expect.

The RSW with side rotary valve gave almost the same power.
I had expected much more from the RSA..
We tested both engines with the same cylinder and piston on the same day, in 2007.
For the RSA we had to shorten the cylinder on the inlet side.
later we re-tested that shortened cylinder on the RSW, it gave less power.
I always felt that the RSA had not been developed sufficiently...
All cylinder development was done on the RSW.
I still feel that the RSA could have been much better....
Later, when I had retired a Honda-type exhaust port was tried.
2HP less...
Very stupid idea I think, if I had still been there I would not have permitted it!!!
I had some ideas about development, but kept them to myself, as I planned to retire...
The flow into and inside the crankcase was not ideal I thought.

[diesel pig]

The RSW with side rotary valve gave almost the same power.
I had expected much more from the RSA..
We tested both engines with the same cylinder and piston on the same day, in 2007.
For the RSA we had to shorten the cylinder on the inlet side.
later we re-tested that shortened cylinder on the RSW, it gave less power.
I always felt that the RSA had not been developed sufficiently...
All cylinder development was done on the RSW.
I still feel that the RSA could have been much better....
Later, when I had retired a Honda-type exhaust port was tried.
2HP less...
Very stupid idea I think, if I had still been there I would not have permitted it!!!
I had some ideas about development, but kept them to myself, as I planned to retire...
The flow into and inside the crankcase was not ideal I thought.

Amazing, I know you were not happy with the exhaust pipe, but to know you thought the inlet was not the best either, I think shows you were right to think there was more power to be had from the RSA.

[jamathi]

Amazing, I know you were not happy with the exhaust pipe, but to know you thought the inlet was not the best either, I think shows you were right to think there was more power to be had from the RSA.

On the dyno we once tested the RSA with a straight and curved exhaust pipe.
The curved pipe gave a little bit less power...
maybe 0.5 HP.
Later it was always tested with the curved pipe..
It might have been better to design the engine with a rear exhaust and the inlet on the front side...
Also, the necessary longer tailpipe needed on the bike cost some power...

[husaberg]

The RSW with side rotary valve gave almost the same power.
I had expected much more from the RSA..
We tested both engines with the same cylinder and piston on the same day, in 2007.
For the RSA we had to shorten the cylinder on the inlet side.
later we re-tested that shortened cylinder on the RSW, it gave less power.
I always felt that the RSA had not been developed sufficiently...
All cylinder development was done on the RSW.
I still feel that the RSA could have been much better....
Later, when I had retired a Honda-type exhaust port was tried.
2HP less...
Very stupid idea I think, if I had still been there I would not have permitted it!!!
I had some ideas about development, but kept them to myself, as I planned to retire...
The flow into and inside the crankcase was not ideal I thought.

When were you given free choice over the pipes?,i seem to remember something about being obliged to use a certain design earlier.
I also seen something i had missed eariler, where either you or Frits mentioned the Reed Derbi had a much larger crankcase volume than the Aprilia.

[diesel pig]

On the dyno we once tested the RSA with a straight and curved exhaust pipe.
The curved pipe gave a little bit less power...
maybe 0.5 HP.
Later it was always tested with the curved pipe..
It might have been better to design the engine with a rear exhaust and the inlet on the front side...
Also, the necessary longer tailpipe needed on the bike cost some power...

Every time you post on the RSA, you open my mind to what could be possible in the future.

[Rudex]

If you widen the boost port on the TM side , and shift the B rear wall over as well , the exit angle would be I believe almost identical to the RSA
but crossing closer to the bore center.
The A rear wall crosses at the same 75% point as the B front and rear. But the A front should be closer to the boost at 78%.
Having each side marked as A and B is confusing things as well, should be RSA and TM.

It would be similar to that:

355086

[wobbly]

Swap the TM A port front/rear wall crossing points - the front wall pointed back the most.

[jamathi]

When were you given free choice over the pipes?,i seem to remember something about being obliged to use a certain design earlier.
I also seen something i had missed eariler, where either you or Frits mentioned the Reed Derbi had a much larger crankcase volume than the Aprilia.

The REED-DERBi had a much smaller crankcase volume than the RSA...

[husaberg]

The REED-DERBi had a much smaller crankcase volume than the RSA...
I think I was thinking this, maybe Frits was referring to intake track volume?


Jan did not enlarge the crankcase volume on the Derbi reed valve engine; it was already big; a reed case has a lot more volume than a rotary valve duct.


I think this was the quote I was looking for last page I think it was from pitlane.



Summary: you need a large crankcase volume. Ideally all of this volume should be situated in the transfer ducts. In real life you will also need to lodge part of this volume between crankshaft and piston, i.e: use a long con rod. Avoid nooks and crannies. Crankshafts should be small and smooth. Big end bearings must never be shrouded by recesses in the crank webs or by stuffers.


n theory enclosed cranks are good. Jan Thiel did some experiments at Aprilia with a kart engine that had its reed valve at the front: the incoming mixture had to move against the direction of crank rotation. And although the crankcase stretched over the crank webs, reversing the direction of rotation brought another HP. So the crankshaft does have an influence.
But in practice, if you reduce the distances between crankshaft and crankcase walls to less than 1 mm, the viscous friction of the mixture between the surfaces really costs power at high rpm. And if you make the clearances so tight that lubricating oil can no longer reach the big-end and crankshaft bearings, it will also cost engines
Another negative aspect: any volume with a narrow 'entrance' between the crankshaft and crankcase surfaces acts as an hydraulic damper on the Helmholtz-resonance in the crankcase.
Aprilia has avoided this by making the space between the crank webs as wide as the big-end bearing. As a result the crankcase volume of the 125 cc RSA engine at TDC is about 650 cc,(or 675 maybe) so the exhaust pipe really has some volume to breathe from.
So much for the fairy tale of high crankcase compression

most of this is frits

With the RSA/ RSW Most of the volume is concentrated in the transfer ducts. Then there is the volume inside the piston of course, and the 1 mm shear-avoiding clearance at all surfaces of the crank.
But that is not nearly enough volume. If you take another look at the Aprilia crank below, you will notice that the space between the crank webs is the same as the space needed for the big end bearing. In other words: the crank webs have flat insides, good for another 60 cc or so, if I remember correctly.
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=310767&d=1615032315&thumb=1 (https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=310767&d=1428930813)
Additional benefits: the con rod has an easier time pushing the mixture aside as it moves between the webs, and the big end bearing gets a lot more cooling and lubrication because it is not shrouded in any way.
Because there are no overhung bobweights, the crank webs are stuffed with tungsten to get the balance factor right.
In the RSA125, the con rod was lengthened from the RSW's 115 mm to 120 mm to create even more crankcase volume.

The paddling is a mixed blessing; it creates aerodynamical drag but it also greatly improves the homogenity of the mixture.
Smooth, full-circle crank webs have the advantage that there is little mixture hiding in nooks and crannies. An example of it's importance: in a certain engine there were 20 mm spaces between the crankshaft bearings and the seals. these ill-accessible volumes acted as pneumatic dampers on the crankcase pressure fluctuation. Filling those volumes with plastic bushes gave a measurable improvement.

Summary: you need a large crankcase volume. Ideally all of this volume should be situated in the transfer ducts. In real life you will also need to lodge part of this volume between crankshaft and piston, i.e: use a long con rod. Avoid nooks and crannies. Crankshafts should be small and smooth. Big end bearings must never be shrouded by recesses in the crank webs or by stuffers.

The picture below shows, wait for it, an RSA125-crank with stuffers...
After Jan Thiel went into retirement in 2008, some geniuses at the factory grabbed their chance to 'correct' the errors that Jan left behind, without even testing the result because 'everybody knows the smaller the crankcase volume the better'. But they never could understand why a 2011 RSA125 was slower than a 2007 model (just look at the 125 cc top speeds on any GP-track). O, the joy of working with Italians.....

[wobbly]

I think Jans passing comment that the RSA could have been better if the valve was on the front with a rear Exhaust seems quite prophetic.
Yes a rear ( straight ) pipe would make more power , as would the shorter stinger , but I have read several comments that the RSW chassis handled
better due to the RSA front pipe header dictating negatively the engine position in relation to the front wheel.

Dr Henise and I are doing a project at the moment with a parallel twin, like the KTM 250GP engine - firing at 90*, but with twin Rotary Valves across the front
and a balance shaft to drive them as well.

[Storbeck]

Balance shaft perpendicular to driveshaft? My understanding of what would be needed to balance a 45 degree twin is.....shaky ... But it seems like that could work and that would be super cool.

[wobbly]

I dont understand any of your post Storbeck.
It is a parallel twin - like a Banshee , but fires at 0 - 90*.
The balance shaft is needed to correct the wildly varying primary resultant of one piston being at TDC , as the other is at peak velocity half way up the bore.
Thus it is across the front of the engine with bob weights on each end , one being the drive down to the clutch gear on the end of the crank.
It also happens to have two bevel gears to drive the pair of RV blades - as due to the asymmetric firing you cant have a single large valve operating two ports
like a Rotax snow or water craft that fires at 180*.

[husaberg]

I think Jans passing comment that the RSA could have been better if the valve was on the front with a rear Exhaust seems quite prophetic.
Yes a rear ( straight ) pipe would make more power , as would the shorter stinger , but I have read several comments that the RSW chassis handled
better due to the RSA front pipe header dictating negatively the engine position in relation to the front wheel.

Dr Henise and I are doing a project at the moment with a parallel twin, like the KTM 250GP engine - firing at 90*, but with twin Rotary Valves across the front
and a balance shaft to drive them as well.
As you are going to have to space out the cylinders for clearance with the transfers anyway if it was a supersized sharred single disc with twin ports wouldn't it have a better time area period. Than twin small discs? simplier drive to.
i am thinking like a jetski or snowmobile rotax.
https://thecrankshopvt.com/pub/media/catalog/product/cache/fb46863f2ce5948910bbdf26f5e36b6a/4/4/440.JPG

[Grumph]

That example has already been compromised - probably by packaging constraints. The inlets are not on the cylinder centerlines.

The bigger the single disc the harder it becomes to package it.

The simplest drive for this layout is a twisted toothed belt. But if the drive can also be a balance shaft there is logic to the layout.

[husaberg]

That example has already been compromised - probably by packaging constraints. The inlets are not on the cylinder centerlines.

The bigger the single disc the harder it becomes to package it.

The simplest drive for this layout is a twisted toothed belt. But if the drive can also be a balance shaft there is logic to the layout.
that one is slightly offset but wobs need not be. Whilst every design is a compromise, the winner has less compromises where it really matters, or has advantages that outweigh they ones the decided to make.
That said i have never seen the drive you had on the supercharged kawa.

[diesel pig]

As you are going to have to space out the cylinders for clearance with the transfers anyway if it was a supersized sharred single disc with twin ports wouldn't it have a better time area period. Than twin small discs? simplier drive to.
i am thinking like a jetski or snowmobile rotax.
https://thecrankshopvt.com/pub/media/catalog/product/cache/fb46863f2ce5948910bbdf26f5e36b6a/4/4/440.JPG

I have not worked out the numbers but I do not think a single disc would work with parallel twin with big ends spaced 90* apart. I am sure the inlet timing would not work.

[Grumph]

that one is slightly offset but wobs need not be. Whilst every design is a compromise, the winner has less compromises where it really matters, or has advantages that outweigh they ones the decided to make.
That said i have never seen the drive you had on the supercharged kawa.

Just a 30mm wide polyvee belt. Never gave a problem.

[husaberg]

I have not worked out the numbers but I not think a single disc would work with parallel twin with big ends spaced 90* apart. I am sure the inlet timing would not work.
Hadnt considered that:blank:
I actually missed that I thought wob had had issues with the tss500 with the 90 set up.? rocking couple I assume?
I think at least one version if not all the KTM twins were 90.s. so maybe smaller bore and less spread still works?

[Frits Overmars]

I have not worked out the numbers but I do not think a single disc would work with parallel twin with big ends spaced 90* apart. I am sure the inlet timing would not work.In theory it could work, but you'd need a huge disc, causing so many other problems that it wouldn't be feasible.
355088

[flyonly]

Just a 30mm wide polyvee belt. Never gave a problem.

Do you not need a toothed belt to keep the timing of the valve?


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[Peter1962]

I think Jans passing comment that the RSA could have been better if the valve was on the front with a rear Exhaust seems quite prophetic.
Yes a rear ( straight ) pipe would make more power , as would the shorter stinger , but I have read several comments that the RSW chassis handled
better due to the RSA front pipe header dictating negatively the engine position in relation to the front wheel.

Dr Henise and I are doing a project at the moment with a parallel twin, like the KTM 250GP engine - firing at 90*, but with twin Rotary Valves across the front
and a balance shaft to drive them as well.

Sounds fantastic. Will you also incorporate Fletners 'sliding gibs' on the intake ?

[wobbly]

It does not matter how you drive it , a single RV has two issues.
Firstly getting the ports on bore center needs a huge valve, creating large unwanted increases in rotating friction and inertia that has to be accelerated.

Not getting the inlets symmetric on the bores proved to be a big power issue in the CPI Cheetah cylinders designed to fit on the Banshee bottom end.
The large CR250 reeds were offset 10mm each side of the centerlines to make them fit, and no matter what we did that asymmetric flow entering the cylinder ruined the scavenging
so badly it was very obvious on the piston wash , and power was severely reduced.
I fitted slightly smaller reeds , back on center , with a stuffer plate down one side and that fixed everything immediately.

But no matter how I visualize it I cannot see how the single valve can achieve asymmetric timing events that are spaced out 90* apart.
It works perfectly in a 180* twin as per the Rotax snow and watercraft , as the opening and closing events occur evenly across the valves horizontal axis - but
those ports are nowhere near on center.

Having the balance shaft across the front makes it easy to implement that as the RV driver as well ,and the bevel system is well proven in the Rotax engines.
That balance shaft is mandatory as I discovered , much to my annoyance with the TSS500 , and of course KTM knew this and used one to correctly balance their 90* odd fire 250GP parallel twin.
And finally yes , stealing Niels Gibb System makes perfect sense ,as long as we dont copy KTM and try to patent the damn thing.

[Grumph]

Do you not need a toothed belt to keep the timing of the valve?


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Husa sidetracked into 4T territory. It drove a Roots supercharger.

[F5 Dave]

It does not matter how you drive it , a single RV has two issues.
Firstly getting the ports on bore center needs a huge valve, creating large unwanted increases in rotating friction and inertia that has to be accelerated.

Not getting the inlets symmetric on the bores proved to be a big power issue in the CPI Cheetah cylinders designed to fit on the Banshee bottom end.
The large CR250 reeds were offset 10mm each side of the centerlines to make them fit, and no matter what we did that asymmetric flow entering the cylinder ruined the scavenging
so badly it was very obvious on the piston wash , and power was severely reduced.
I fitted slightly smaller reeds , back on center , with a stuffer plate down one side and that fixed everything immediately.

But no matter how I visualize it I cannot see how the single valve can achieve asymmetric timing events that are spaced out 90* apart.
It works perfectly in a 180* twin as per the Rotax snow and watercraft , as the opening and closing events occur evenly across the valves horizontal axis - but
those ports are nowhere near on center.

Having the balance shaft across the front makes it easy to implement that as the RV driver as well ,and the bevel system is well proven in the Rotax engines.
That balance shaft is mandatory as I discovered , much to my annoyance with the TSS500 , and of course KTM knew this and used one to correctly balance their 90* odd fire 250GP parallel twin.
And finally yes , stealing Niels Gibb System makes perfect sense ,as long as we dont copy KTM and try to patent the damn thing.

Interesting. The Cheetah kit comes with rubber manifolds that are also offset to move the carbs closer together.
On top of that they crack, as I found when I couldn't understand the tuning got worse and worse until I looked down with tank off. . Can I see . . ? Pokes finger in hole. Oh shit. Billet ones fixed issue but central shot. Custom made Airbox didn't fit anymore. Grr.

[diesel pig]

In theory it could work, but you'd need a huge disc, causing so many other problems that it wouldn't be feasible.
355088

I will have to admit I was only thinking about a Disc the size in Husaberg's picture But thank you and Wobbly pointing out it could be done with a bigger Disc but in it's self would lead to bigger problems.

[Storbeck]

I dont understand any of your post Storbeck.
It is a parallel twin - like a Banshee , but fires at 0 - 90*.
The balance shaft is needed to correct the wildly varying primary resultant of one piston being at TDC , as the other is at peak velocity half way up the bore.
Thus it is across the front of the engine with bob weights on each end , one being the drive down to the clutch gear on the end of the crank.
It also happens to have two bevel gears to drive the pair of RV blades - as due to the asymmetric firing you cant have a single large valve operating two ports
like a Rotax snow or water craft that fires at 180*.

Somehow my mind turned 90 Deg into 45 degree then pictured something that makes no sense in retrospect.

Sounds like a very cool project.

[crbbt]

this parallel twin wouldn't happen to be about 600cc would it?

[wobbly]

Have a think about how long a 300cc pipe would be , off the back of a reverse cylinder parallel twin engine.
Not going to happen.

[husaberg]

Have a think about how long a 300cc pipe would be , off the back of a reverse cylinder parallel twin engine.
Not going to happen.
So if its an LSR bike (my guess) if this is the case what is the advantage of the 90 deg crank?

[Frits Overmars]

Have a think about how long a 300cc pipe would be , off the back of a reverse cylinder parallel twin engine.
Not going to happen.Unless your name is Robin Tuluie. This is his 800cc Tularis vibrator two-stroke twin. The pipes seem to fit; the silencers may be less convincing.
355091

[Storbeck]

So if its an LSR bike (guess my guess)what is the advantage of the 90 deg crank?

I'm guessing it has to do with the pistons coming to a stop and changing direction at top and bottom of their stroke. 180 degree firing they are both doing it at the same time, 90 Deg firing one is mid stroke when the other is at top or bottom.

Possibly to reduce fluctuations in rpm or maybe it's a vibration thing. (Or both).

[Frits Overmars]

I'm guessing it has to do with the pistons coming to a stop and changing direction at top and bottom of their stroke. 180 degree firing they are both doing it at the same time, 90 Deg firing one is mid stroke when the other is at top or bottom.
Possibly to reduce fluctuations in rpm or maybe it's a vibration thing. (Or both).You are on the right track Storbeck.
In a 90°-firing twin, the fluctuations in the torque curve per revolution are much more gentle than in a 180°-firing twin.

[Flettner]

360cc reverse cylinder

[Grumph]

I wouldn't want to try and outbrake that into a tight corner.

Anything been said at scrutineering about pointy bits ?

[wobbly]

No its not a LSR engine , its a track day roadracer.
The Tularis pipes were past a vertical line up from the rear tire , thus illegal before even fitting mufflers.
Sure Niels thing fits with swoopy bends , but getting two in would be akin to self flagellation - and having mid section bleed tubes takes more room and is
a packaging nightmare.
The 90* firing is proven " Big bang " theory , plenty of reasons to do this , even though it requires two discs to accomplish with odd fire.
I got close to 100Hp from a 400cc Banshee with the worst transfer ducts on the planet , and in a RS250 Cup Chassis it weighed just over 100Kg.
With an easy 120Hp on tap and Niels Gibbs providing torque like a tractor, in this case smaller is going to be better.

[Grumph]

No its not a LSR engine , its a track day roadracer.
The Tularis pipes were past a vertical line up from the rear tire , thus illegal before even fitting mufflers.
Sure Niels thing fits with swoopy bends , but getting two in would be akin to self flagellation - and having mid section bleed tubes takes more room and is
a packaging nightmare.

I agree with the point on packaging two long pipes.

But the vertical line up from the rear tyre is I think an FIM reg.
Some years back while scrutineering I had an annoying pest hanging around who tried to quote the FIM rulebook at me.
It took some very direct and not polite conversation to convince him that locally at least we worked to the MNZ rulebook
and until we ran a meeting under an FIM permit he could keep his FIM rulebook in a safe "personal space."

So before abandoning a layout, check your local rules.

[wobbly]

Good point Grumph , but the Dr will race it in the USA where the same rule about " pointy bits " past the rear tire applies.
But truth be told I wouldn't be comfortable having those things out the back - legal or not.

[Flettner]

Here is a more modern picture, a little more sensible pipe outlet.

[Flettner]

Speaking of pointy pipes, this was my Uniflow 440 engine in a jet boat for load test. This run involved these four pipes, mid section bleeds. I drove to the Hamilton boat ramp in the middle of town just down at the river from the police station, where we usually did test runs.

Well it appeared we arrived right in the middle of some police practice exercises at the boat ramp. I had not even got out of the car when there appeared two officers at my car door. They were very concerned about the four 'missiles' sticking out of the back of the boat.
It took quite some time to quell their fears, even having to show where the pipes were attached to the engine. They never the less kept their eye on me.
Had I known the police were there, Id have painted some red and yellow tips on the sharp end of the chambers for effect and made them really look like missiles 😁.
Probably would have been locked up for that.

[Frits Overmars]

Here is a more modern picture, a little more sensible pipe outlet.Any difference in behaviour compared to the side bleed pipe?

[Rudex]

Swap the TM A port front/rear wall crossing points - the front wall pointed back the most.

Yes, You are right!.

I find it curious that the port A front wall is further back than the rear wall. Why not every wall in 75%?.

For global view, what are the ports A&B radial position (angle or %) and axial angles?.

Best Regards.
355095355096

[beta]

Yes, You are right!.

I find it curious that the port A front wall is further back than the rear wall. Why not every wall in 75%?.

For global view, what are the ports A&B radial position (angle or %) and axial angles?.

Best Regards.
355095355096

TM has nothing to do with that picture

[Flettner]

Any difference in behaviour compared to the side bleed pipe?

Too hard to tell, there were so many problems with the tuning at the start that I changed it back to what I was comfortable with. Tuning the EFI on this project has turned out to be somewhat of a problem. Even switched back to normal TPI.
Turned out it was a combination of aulternator not keeping up, and a few other issues, where have I seen that before. ��

Pissing around with this twin port AG100 has taken my attention (and resources) for the time being.

[bad'rule]

Hello everyone,
I've joined KB for sometimes now and have read everything ESE thread.(I think I didn't missed any pages . I love to be accepted in KB ,TQ again)

Seems that, I couldn't find any talks here in KB ,regarding bore thickness meassures.

A question on Air-cooled 125cc engine.
What would be the good thickness cyl.bore for any given piston?

I know the facts that, the bigger the piston gets, the thinner standard cyl bore wall will be and at some stage of the size they loosing power easily when engine get hot .

Here in SEA country, the best sleeves we can only easily get is "disel sleeves" .

TIA.

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[husaberg]

Despite it raining 170 mm the day before and the Grey river being in full flood with all 4 roads leading to the coast being shut the day before with slip, flooding ,rock falls and snow.
If that wasn't enough in the first practice a diesel bucket oiling the whole track leading to the whole track having to foamed then be washed off by the fire brigade.

Greymouth put the 35th annual street race without it even raining.

Live feed
https://www.facebook.com/watch/live/?ref=watch_permalink&v=1748924202180366

Those observant will notice there is one one left corner the rest being the laeast favoured right hand bends
This was due to the original officials wisely noticing it would be far too fast in the traditional rotation.

[wobbly]

bad'rule , my choice would be a 5mm aluminum sleeve pressed in, and welded in at the top and bottom.
Then get it plated after final porting - check with the plater what type of alloy is suitable.

On another topic re drag racing in Thailand and Malaysia , the EngMod users FB group are thinking of doing a pipe design shootout , as a means to help people to learn
how to use the code more effectively.
One suggestion was to use an engine that isnt " common " like a 125 or 250.

The KR150 seems to win everything in Thailand/Malaysia as it was built there ,so I thought that would be a good choice.
Do you have access to a stock one of these that could be measured and entered into a sim.
The other one would be a TZM150 , but I believe these were made in only in Vietnam as I have done several of those , but all bored and stroked.

[bad'rule]

Thank you Wobbly for your answers ,even tho it was for water cooled engine. Still good to have that information in hand.

Thailand is the best in our region here for racing thingy even in the past they beat us on race machinery .Im not so into drags anymore, mates still race them. Things get very costly for us over here nowdays actually.
It Would be great to know and watch your works race Wobbly.[emoji106]

I was hoping an answers for Air Cooled Engine if any one know,please
,TIA

-Badrule-

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[wobbly]

The 5mm sleeve would work just as well in an aircooled, even better in fact as the thermal transfer thru the plating and alloy would
be far superior to a cast sleeve.

[bad'rule]

Okay Wobbly, i will just follow your suggestions then ,ThankYou again.



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[Haufen]

I would love to see a typical power curve of those bikes. Has anyone seen something by chance?

And does anyone happen have to a KR150 EngMod Pack file they would share?



The KR150 seems to win everything in Thailand/Malaysia as it was built there ,so I thought that would be a good choice.
Do you have access to a stock one of these that could be measured and entered into a sim.
The other one would be a TZM150 , but I believe these were made in only in Vietnam as I have done several of those , but all bored and stroked.

I was wondering the same in April. No luck so far, unfortunately.

I think there was a Mota Shootout on another board about 20? years ago. I don't remember much about it, except that it was fun and didn't turn into a pissing contest.

[jamathi]

The 5mm sleeve would work just as well in an aircooled, even better in fact as the thermal transfer thru the plating and alloy would
be far superior to a cast sleeve.

In 1974 I made a conical sleeve, Morse cone. It was very easy to fit and remove, worked great!!!
No welding needed, just a light press fit. I pressed it in about 2mm.
I got the sleeve material from MAHLE, so I was sure it could be plated... MAHLE 138
Once I had to make a cylinder in a hurry, no time to get it plated.
So I bought a plated Kreidler cylinder, and made a conical sleeve out of it...
It gave good power, and won a lot of races!!
First I made it without aux ports: insufficient power....
As it was easily removable I took it out and added aux ports: +2.5 HP...
Less than 1 hours work, my client was very happy, and won a Dutch NMB championship with it.

[Frits Overmars]

I am very happy too as that cylinder now has pride of place in my cabinet, together with a cylinder of the world champion Suzuki RK67 50cc twin and a cylinder of the Garelli 125cc twin, good for six world titles, all given to me by Jan.

[Mollihead]

Hello everyone,

I‘m a longtime reader of this thread and appreciate a lot the experience which all of you share to keep 2 strokes alive!
I‘m living in Germany and during corona time I started tuning my 1976 Zündapp 50cc moped. Ended up with 64cc aircooled and reliable 18,5HP.
Now the next step is 98cc (50mm x 50mm Bore x stroke).
Target in the range of 25HP.
There are not so many cylinders out there - so I have to use one with a T shaped port.
Many times I could find pictures of ideal shape of a single port but nothing about ideal T-port dimensions.
Can somebody explain the ideal shape? Is it a horizontal line? Or should it be lower towards the sides to prevent damage of the ring?

[wobbly]

All the GP Honda A kit cylinders had a dead flat timing roof , but years ago I did a test by reversing the normal shape and had the outer edges opening first.
This gave a good power increase , with the same timing as previously.
The reasoning was that the initial exiting wave front , that would normally be smeared out in time and amplitude , due to the considerable path length differences
would be helped by the geometry change - it worked.
Ring damage isnt an issue , as the center bridge gives support no matter what the shape.
The bridge relief is very much an issue though.

[Mollihead]

Thanks Wobbly!

I have seen your post about outer edges opening first.
For now I will try the horizontal line.

Another topic is the maximum width of inlet port with a bridge in the Center.
My last try seemed to be too wide and in the end I had a crack in the piston skirt.
Is there a rule of thumb like xy % of bore width ?

[TZ350]

There are not so many cylinders out there - so I have to use one with a T shaped port.
Many times I could find pictures of ideal shape of a single port but nothing about ideal T-port dimensions.
Can somebody explain the ideal shape? Is it a horizontal line? Or should it be lower towards the sides to prevent damage of the ring?

Team ESE has run exhaust T ports with a center divider and tried all sorts of configurations. Currently ours is higher on the outside and lower at the bridge.

The theory is, when you get it right. With a head start, about 2deg . The gases from the outer edges arrive at the exhaust duct nozzle at the same time as the gases from the lower bridge area as they have a shorter path.

It is hard to be definitive, but it does seem better. Or at least runs better. and 2deg might not be the ideal, more experimenting is required.

355128 355127 NSR250 MC21 Cylinder.

May or may not be ideal but it has done a few furious races and is still going strong. So mechanically an OK idea at least.

[Mollihead]

Hi TZ,

That’s very interesting.
The theory is, when you get it right. With a head start, about 2deg . The gases from the outer edges arrive at the exhaust duct nozzle at the same time as the gases from the lower bridge area as they have a shorter path.

This is a little bit confusing to me since the exact same theory didn’t worked with triple exhaust port and ended with having auxiliary ports lower than main port !?

[Wos]

In 1974 I made a conical sleeve, Morse cone. It was very easy to fit and remove, worked great!!!
No welding needed, just a light press fit. I pressed it in about 2mm.
I got the sleeve material from MAHLE, so I was sure it could be plated... MAHLE 138
Once I had to make a cylinder in a hurry, no time to get it plated.
So I bought a plated Kreidler cylinder, and made a conical sleeve out of it...
It gave good power, and won a lot of races!!
First I made it without aux ports: insufficient power....
As it was easily removable I took it out and added aux ports: +2.5 HP...
Less than 1 hours work, my client was very happy, and won a Dutch NMB championship with it.

Mahle 138 should be AlSi18CuMgNi 😉

[Storbeck]

Hi TZ,

That’s very interesting.
The theory is, when you get it right. With a head start, about 2deg . The gases from the outer edges arrive at the exhaust duct nozzle at the same time as the gases from the lower bridge area as they have a shorter path.

This is a little bit confusing to me since the exact same theory didn’t worked with triple exhaust port and ended with having auxiliary ports lower than main port !?

I was thinking the same thing.

[bad'rule]

Jamathi, Thank you for your idea , they have been proven to be reliable and,it even won in the race too.
Bonus on easier sleeve changing there.

I will give it a try on these one and with what Wobbly suggest for thickness.
[emoji106]



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[Niels Abildgaard]

Some students and I visited a gokart engine manufacturer (Dino) in Middelfart ,Denmark many years ago
They used centrifugal cast iron for cylinder liners,modified on fridays, and many copies were sold on mondays if they had won on saturdays.
If the reason for aluminium and nikasil being prefered today is better heat transfer,then unplated bronze bearing metal could be cheaper for one offs.
Has it been tried and why not?

[wobbly]

The triple port geometry is optimized by creating the highest amplitude , shortest duration wave front into the duct , and this means the main port is out at maximum width around 70% of bore.
This is not only the optimum width for ring life but also creates the least path length difference whilst giving the maximum Blowdown area at EPO.
Once this initial wave is established into the duct , heading for the diffuser , the Aux ports , being lower and having considerably less pressure delta across them
subsequently play more of a part in simple Blowdown pressure bleed, rather than creating another high intensity wave with a much longer path length.

In a T port you are stuck with the large path length difference , no matter what the geometry ,so you have a choice of the outer , longer path timing being below , equal to ,or above.
All are a serious compromise , but one ameliorates the shapes down side better than the other two.
In a 3 port the geometry happens to be the least compromised with the outer edges being lower.

[Grumph]

Some students and I visited a gokart engine manufacturer (Dino) in Middelfart ,Denmark many years ago
They used centrifugal cast iron for cylinder liners,modified on fridays, and many copies were sold on mondays if they had won on saturdays.
If the reason for aluminium and nikasil being prefered today is better heat transfer,then unplated bronze bearing metal could be cheaper for one offs.
Has it been tried and why not?

It's one of those awkward trade-offs. Phosphor bronze would probably be too soft to run steel rings against. The harder Bronzes - like Admiralty Bronze
can be quite brittle.
Cost wise,there's probably not a great difference between plated alloy and bronze. The price of Copper currently makes bronze quite expensive.
Plus you'd have to buy it as hollow bar - which is very thick wall so you'd have a lot of wastage.

[speedpro]

Or Ken Steadman at PHOENIX FOUNDRY LIMITED could probably cast sleeves to a size you want. He could also customize the alloy which I know he's done on at least one job.

[dutchpower]

Mahle 138 should be AlSi18CuMgNi 😉

Mahle 138

G - ALSi18CuNi

[husaberg]

Some students and I visited a gokart engine manufacturer (Dino) in Middelfart ,Denmark many years ago
They used centrifugal cast iron for cylinder liners,modified on fridays, and many copies were sold on mondays if they had won on saturdays.
If the reason for aluminium and nikasil being prefered today is better heat transfer,then unplated bronze bearing metal could be cheaper for one offs.
Has it been tried and why not?

Aluminium pistons and aluminium bores popularity I believe is more than just heat transfer but also as their expansion rates are closely matched which as well as matching heat transfer helps stop the transfer of aluminium onto the iron cylinder:msn-wink:

[Frits Overmars]

Aluminium pistons and aluminium bores popularity I believe is more than just heat transfer but also as their expansion rates are closely matched which as well as matching heat transfer helps stop the transfer of aluminium onto the iron cylinder:msn-wink:Just how closely do you want the expansion rates of piston material and cylinder material to match? The ideal would be 1 to 1 if piston temperature and cylinder temperature were equal.
But they're not. The piston gets a lot hotter than the cylinder, so its expansion rate should be lower, like a steel piston in an aluminium cylinder.
It does work on foulstrokes. The problem is that the dome surface temperature of the steel piston would be sky-high, and two-strokes do not like that.
Foulstroke manufacturers get away with it by cooling the piston from below with multiple oil jets. In crankcase-scavenged two-strokes we cannot have that luxury.
355131

[lohring]

Very small racing engines have used chromed brass sleeves with ringless high silicon aluminum pistons. This seems to work for up to around 15 cc engines, but ringed pistons work better with the same materials in larger sizes. Quite a few 2 to 10 cc engines were made with cast iron ringless pistons in cast iron sleeves. Really small engines have been built with hardened steel pistons in steel sleeves. Careful machining is needed to make these combinations work.

Lohring Miller

[Frits Overmars]

We use alloys with a silicon content of over 30% for pistons: https://www.rsp-technology.com/
The silicon keeps the expansion coefficient under control. The downside is that alloys containing so much silicon will eat milling cutters for breakfast.
https://www.youtube.com/watch?v=ZwbEuzJCnqI

[katinas]

.....then unplated bronze bearing metal could be cheaper for one offs.
Has it been tried and why not?

I tried a liner made out of aluminum bronze (with 6% of iron and nickel) without coating, it works fine without any siezing, but it wore out quickly. Ater that bought RG7 bronze, but never tested.

[Muciek]

Here guy have cast a cylinder from aluminium like used in Porsche/Audi/BMW/mercedes engine blocks (ALUSIL) and honed it with special paste afterwards, wait week or two so he will probably get it running.

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

Whole road to getting a good casting https://www.youtube.com/watch?v=sX7WZUwd1lM&list=PLfcX_sTOJWP7hxVJqtWBJRRCuP1DnEGov

[pete376403]

Here guy have cast a cylinder from aluminium like used in Porsche/Audi/BMW/mercedes engine blocks (ALUSIL) and honed it with special paste afterwards, wait week or two so he will probably get it running.

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


Whole road to getting a good casting https://www.youtube.com/watch?v=sX7WZUwd1lM&list=PLfcX_sTOJWP7hxVJqtWBJRRCuP1DnEGov


Sound the same as Chevrolet did with the Corvair blocks - cast in high silicon aluminium, then the bores were etched with acid(?) to erode the ally and leave the siiicon as a wear suface for the rings

[Frits Overmars]

Sound the same as Chevrolet did with the Corvair blocks - cast in high silicon aluminium, then the bores were etched with acid(?) to erode the ally and leave the siiicon as a wear suface for the ringsYup. And some Porsches. And some Mercs. And probably others.

[Flettner]

We use alloys with a silicon content of over 30% for pistons: https://www.rsp-technology.com/
The silicon keeps the expansion coefficient under control. The downside is that alloys containing so much silicon will eat milling cutters for breakfast.
https://www.youtube.com/watch?v=ZwbEuzJCnqI
And heat transfer is poor.

[Flettner]

Wobbly, what down angle on exhausts? I wrote it down somewhere, probably on a peice of wood, then promptly used it for pattern making somewhere.
27 degees rings a bell.
The square bore and stroke twin port, water cooled, powervalve cylinder emerges. Straight ports this time not curved like the air cooled cylinder. Hold down studs come up from underneath so free hand in where the exhausts go, no need to compromise for nut fitment or room for a spanner.

[husaberg]

Just how closely do you want the expansion rates of piston material and cylinder material to match? The ideal would be 1 to 1 if piston temperature and cylinder temperature were equal.
But they're not. The piston gets a lot hotter than the cylinder, so its expansion rate should be lower, like a steel piston in an aluminium cylinder.
It does work on foulstrokes. The problem is that the dome surface temperature of the steel piston would be sky-high, and two-strokes do not like that.
Foulstroke manufacturers get away with it by cooling the piston from below with multiple oil jets. In crankcase-scavenged two-strokes we cannot have that luxury.
355131
To deal with this we build in taper ,ovality, cam grinds and cut outs even splits and in old ones wire winds and also expansion strips or fillets as in your pic
As well as the oil jets they use more rings, oil on the cylinders and a cooling stroke with much less output per area.
then you throw in the slippery coating and the groves for oil.
I am not sure on a 2t how much heat is transmitted from the rings but on a 4t from what I have read on its far more than most people appreciate.
In an ideal world the 4t skirt will expand just enough to increase the surface area to again be able to transfer the heat when needed.
I was trying to find the clearance on a modern 4T big twin that was mentioned the other day but it was tiny, but then again so was its output/liter.;)
(edit)Victory air-cooled engine 2nd gen was 25 micron or 1.5 thou. On a 850 cc cylinder 101mm bore.

The piston in your pic
A late model MX bike is now very similar. just with more aluminium to bake up for the 1/3rd strength
My son races YZ450f Supermoto, even with its GYTr twin oil jets the fully synthetic oil changed at about 30 minutes, the piston is good for 8 hours the camchain less then 4.
no big deal other than how bloody much harder it is to do than a 2t is.
3x the cc of a RSA and only a few more hp.
https://cross-mania.com/24085-large_default/piston-athena-big-bore-o102mm-500cc-for-yamaha-yzf-450-from-2010-to-2017.jpg
the cutouts below the bottom ring land are to get the pin in and out

[wobbly]

Neil , 25* is optimum.
And the other posts mentioned point is that the majority of heat dissipation from the piston ,out to the bore in a 2T occurs on the bottom ring seal face.
The very first sign of deto starts at this surface - resulting in the term " power deto " coined by Franco Drudi of TM Championship winning fame ( my boss ).
As this process creates free radicles that start eating away at the hottest surfaces trying to recombine the single free electrons that are a result of the detonation phenomenon.
Creating deto uses up a huge amount of the available fuel energy , and this is what we use when data logging the EGT , as it initially flat lines with the first over lean jet change
then drops with the next.

[Flettner]

Best I write it on the shed wall, so I can't lose it in the future. ��
Thankyou.

[katinas]

Steel pistons with iron cylinders were used in Anzani radial engines from 1909.
Later British Anzani produce very interesting two stroke boat racing engines, with combined piston port and rotary intake through the center of crank webs.

[Niels Abildgaard]

Steel pistons with iron cylinders were used in Anzani radial engines from 1909.
Later British Anzani produce very interesting two stroke boat racing engines, with combined piston port and rotary intake through the center of crank webs.

Where have You found these pictures or engines?
The boat engine is interesting and looks like a Trabant but with much fewer parts.

[katinas]

Where have You found these pictures or engines?
The boat engine is interesting and looks like a Trabant but with much fewer parts.

I took piston pictures in the Italian Air Force Museum at Vigna di Valle, on Lake Bracciano. I went to the museum with my son this year, because he is very interested in military planes and especialy wanted to see the real, fastest red hydroplanes from "Porco Rosso". Apart many interesting things, unfortunately I didn't see a single two-stroke engine.
Later at home checked Anzani and found this https://www.boatracingfacts.com/forums/showthread.php?1182-British-Anzani-A-amp-B-Stock-amp-Alky-Racing-Engines/page30

[mike schmidt]

Scrolling though Kiwi Bikers this morning and the pictures of the Anzani crankcases caught my eye. First think that came to mind was that someone in Europe was epoxying them up just like the ones in my shop. Then I read further and found out the pictures were off Boat Racing Facts. The pictures were posted by John Taylor. A few years ago he got sick and all the Anzani parts were sold to Jim Hunter, a friend of mine. They are in my shop for restoration.

Small world.

[Mollihead]

At the moment I’m searching for a piston fitting to 50mm cylinder.
14mm wristpin
Piston ring at 6 o‘clock. Max 1mm thickness.
Compression height 28-30mm
Cylinder is Nicasil 50mm stroke

Any suggestions?

The piston belonging to the cylinder is from Mahle.
Big chamfer around wrist pin hole which favours short circuiting between Exhaust and A-transfer

[Wos]

At the moment I’m searching for a piston fitting to 50mm cylinder.
14mm wristpin
Piston ring at 6 o‘clock. Max 1mm thickness.
Compression height 28-30mm
Cylinder is Nicasil 50mm stroke

Any suggestions?

The piston belonging to the cylinder is from Mahle.
Big chamfer around wrist pin hole which favours short circuiting between Exhaust and A-transfer

Have a piston from italkit here with ringgap at oposit to main ex

Measured for a quick look comp hight..25

Its from a big bore kit for minarelli am6

But maybe you should have a look at wössner ;)

https://www.woessner-kolben.de/fileadmin/Downloads/Kataloge/Motorrad_Inhalt2018%20print.pdf

[diesel pig]

At the moment I’m searching for a piston fitting to 50mm cylinder.
14mm wristpin
Piston ring at 6 o‘clock. Max 1mm thickness.
Compression height 28-30mm
Cylinder is Nicasil 50mm stroke

Any suggestions?

The piston belonging to the cylinder is from Mahle.
Big chamfer around wrist pin hole which favours short circuiting between Exhaust and A-transfer

Yeah, Wossner and other aftermarket piston manufactories do over size big bore pistons for 85cc MX's that might be the go.

[Mollihead]

I do have Wössner and Wiseco for Suzuki RM85.
But they both have a compression height of 27mm which is only usable for me in case I mill down the casing by 1mm.
Want to avoid that

[husaberg]

I do have Wössner and Wiseco for Suzuki RM85.
But they both have a compression height of 27mm which is only usable for me in case I mill down the casing by 1mm.
Want to avoid that

Honda cr85/100 have a crown height of 24mm
https://www.mitaka.co.uk/piston.php?id=2

there are old school rm100 as well that were 50mm ish based on the 125cc air cooled rm

or YZ is given as being
26.5
https://www.mitaka.co.uk/piston.php?id=78

or troll through Rolfee
https://www.pvlsverige.se/vrm/kolvar/kolvar.html

[Wos]

This is italkit vertex... look at last picture to clarify Dimensions 😉

Comp hight 25,2

https://www.langtuning.de/Italkit-Racing-Kolben-O50-mm-mit-14-mm-Kolbenbolzen

Comp hight 28 but 12mm pin
Maybe change needle bearing 😉

https://www.langtuning.de/LT-Performance-1-Ring-Kolben-90-ccm-50-mm

[Mollihead]

This is italkit vertex... look at last picture to clarify Dimensions 😉

Comp hight 25,2

https://www.langtuning.de/Italkit-Racing-Kolben-O50-mm-mit-14-mm-Kolbenbolzen

Comp hight 28 but 12mm pin
Maybe change needle bearing 😉

https://www.langtuning.de/LT-Performance-1-Ring-Kolben-90-ccm-50-mm

I already ordered this piston and sent it back after I found out that the piston is too short for 50mm stroke. Exhaust port opened at TDC.

The only piston I found is a Polini Evolution P.R.E
Ordered it with 49,935 and received one with 49,915 diameter :mad:
Now I don‘t know whether I should give it a try with 8,5 1/100mm clearance…

[Mollihead]

By the way: in case there is a needle bearing which converts 14mm to 12mm it could be an option.
The only one I know of is offered at EMOT racing page. But it’s always marked as sold out.

[Wos]

By the way: in case there is a needle bearing which converts 14mm to 12mm it could be an option.
The only one I know of is offered at EMOT racing page. But it’s always marked as sold out.

Ex open in tdc??? Really?

New nikasil coating or do a ptfe piston coating for 0,05 to 0,06 mm tolerances
Would be the expensive way....

Talk to emot! 😉 but many dealers have conversion bearings...

Would be nice to hear more ...engine...what you are aiming for...upper needle bearing outer diameter... wide? 😉


But why going that way???

Easy job to take off 3 mm on cilinders downside on a lathe ...then the italkit should fit!?

Pretty much easier than milling case 😀

[Mollihead]

@Wos

The Italkit piston from Langtuning has a skirt length of 46,5.
Therefore it opens Exhaust at TDC in case 50mm stroke.

Regarding the bearing:
At the moment I use a Kart bearing 14x18x16,7 Inner diameter x outer diameter x width
So a conversion bearing should be something like 12x18x….

[Mollihead]

The project is to squeeze out a Zündapp Zuntrade cylinder. Thermosyphon cooled.
Originally 92cc (with 47mm stroke).
Now I have a 50mm crankshaft. Therefore port heights are adjusted accordingly.
Transfer widths are limited - so I extended it with JB Weld.
Added boyesen ports and extended the inlet area to run a VForce 3 membrane.
Since there is not much material left I can’t mill down the bottom end several mm.
Already had a crack in this area in the past.
The last cylinder reached 22,5HP at the wheel before the crack happened.

[41juergen]

I need new big end bearings for a TZ250 4DP. The stock Yamaha ones cost approx. 115,-€! Does anyone have an idea were to get silver caged bearings, ID 24 mm, OD 31 mm, width 16 mm..

[Wos]

@Wos

The Italkit piston from Langtuning has a skirt length of 46,5.
Therefore it opens Exhaust at TDC in case 50mm stroke.

Regarding the bearing:
At the moment I use a Kart bearing 14x18x16,7 Inner diameter x outer diameter x width
So a conversion bearing should be something like 12x18x….

Nice " Stoiga" racer from zündapp :drinknsin 😉

Short piston skirt is opening INLET port earlier...but not ex port

But does this matter on a reed valve inlet?? Opening timing is done only by reeds... confused...

I was wrong that its easy to find this special needle bearing :(

Grüßle 😉 Wolfgang

[Mollihead]

Finally found one today, which I think is from same source as the EMOT ones

https://2taktteile.de/products/adapter-kolbenbolzenlager-14-12-mm-kolbenbolzen-sachs-50s-80sa-80sw-50-5-501?_pos=1&_sid=dd961c628&_ss=r

[Mollihead]

Nice " Stoiga" racer from zündapp :drinknsin 😉

Short piston skirt is opening INLET port earlier...but not ex port

But does this matter on a reed valve inlet?? Opening timing is done only by reeds... confused...

I was wrong that its easy to find this special needle bearing :(

Grüßle 😉 Wolfgang

Hi Wolfgang

I try to show it in the picture. In case length of skirt is shorter as the stroke you can see through the exhaust port in to the crankcase in case piston is at TDC

Gruß zurück Wolfgang <_<

[Wos]

Hi Wolfgang

I try to show it in the picture. In case length of skirt is shorter as the stroke you can see through the exhaust port in to the crankcase in case piston is at TDC

Gruß zurück Wolfgang <_<

Thanks Wolfgang for helping me with picture...never seen...but got it now:weird::brick::shit:

[Mollihead]

never thought about this before until Wobbly somewhere mentioned this. But it’s long time ago…

Now I’m looking for a 50mm piston with
12mm pin
And >=28mm comp height
And skirt length >=50mm
And ring pin at 6 o‘clock

but seems to be not easy as well.

[Wos]

never thought about this before until Wobbly somewhere mentioned this. But it’s long time ago…

Now I’m looking for a 50mm piston with
12mm pin
And >=28mm comp height
And skirt length >=50mm
And ring pin at 6 o‘clock

but seems to be not easy as well.

Lieber Wolfgang ;)

New idea! 😉

Why to stuck with 50,00 mm bore...

For long therm its good to take parts as bearings and pistons that are available everywhere...and overbore the cilinder...replate it

[Mollihead]

Nice idea :yes:
But as mentioned the cylinder is already at the limit of stability.
Therefore I asked some pages back for the maximum inlet width.
I had crack in the piston and cylinder inlet bridge at the same time.

[Mollihead]

My feeling is that many of the available MX pistons are designed to run in a case membrane engine and therefore they have a narrow skirt at the inlet side.
If you use it in a cylinder membrane engine the support at the side is missing and therefore the area pressure at the bridge will be too high at downstroke after combustion

[Wos]

Ask barikit for specific ringpin pos

https://barikit.de/collections/kolben?sort_by=best-selling&filter.v.option.durchmesser=49&filter.v.option.durchmesser=50&filter.p.m.my_fields.kolben_a=28.0&filter.p.m.my_fields.kolben_c=53.5

[Mollihead]

Cylinder is back. Milled down 0,8mm
So I have the possibility to test different pistons.

[Flettner]

AG100 farm bike cylinder. Not flow restricted at the extremities of the exhaust ports like most bridged ports.

[Mollihead]

I’m not 100% sure what I see.
Does it mean each side has has it's own pipe? Crazy!

[Flettner]

I’m not 100% sure what I see.
Does it mean each side has has it's own pipe? Crazy!
Yes, two pipes.

[Mollihead]

Compared to the same exhaust but single - is it an improvement or was it just for fun to see how it works?

[Flettner]

Compared to the same exhaust but single - is it an improvement or was it just for fun to see how it works?

It was to see if I could cast something with max blowdown, time / area .... flow. Not like a normal a bridged port. And yes also for a bit of fun in the Vinduro farm bike class. It has never seen a dyno so no real idea but to say it goes pretty well.
Problems? Building two identical pipes. Ive ended up building press dies to get them the same. It pulls very well down low (6000 and below) in fact I can almost do a whole event under that figure. Top end (7500 to 11500) it pulls hard.... but the transition it falls flat on its face. This being the none power valve air cooled cylinder.
The new cylinder having a welded on water jacket and twin powervalves Im expecting will sort this flat range.
It still has an unfortunatly rubbish bore and stroke at 48 x 58.
Next series engine will correct this at 54 x 54, AG engine Im using now will not accommodate more that 48 stroke.j
It would be interesting to see this twin port design with a 'proper' twostroke tuner involved, not just my semi educated estimates.
Simply put, for the same cylinder exhaust span as a three port this only has one bridge and minimal flow restrictions at the port extremities.

[Mollihead]

I’m surprised to see an aircooled cylinder with that distance between studs.
Normally there is not enough space for two exhaust ports.
I could imagine that standard exhaust resonance calculations are not 100% valid any more in case two resonant pipes talk with each other if exhaust port is in open position.

[Wos]

Think there is risk of loosing energy / temperature caus of you have much more pipe surface.
According to this loss it is difficult to calculate for two pipes...

And if pipes have minimum diffrences ...they talk 😉 against each other... 😞

Maybe the power flat is caused by that

[Wos]

@flettner

How you did calculation for the two pipes? They look fat at belly!?

Maybe you had calculated each pipe with complet cilinder volume!?

Experts 😉

Isnt it better to take half ccm for calculation for 2 pipes arrangement??

Thanks to help my understandig 😉

Wolfgang

[F5 Dave]

We could argue about this for ages.
Just what the thread needs. Stinger has been covered here but it makes sense to me to have the same combined area as a single pipe (so 1/2 by area) and then experiment.

The belly section should be derived using the same angles but starting with a much smaller header pipe. But my brain is melting here and now I've entered a highly suggestable state so I best go for a walk

Anyway 3 cheers to Neil for not just asking the question but committing it to metal.