ESE's works engine tuner

[husaberg]

Came accross this not read it
https://www.scribd.com/document/794820770/Aprilia-RSA-125-Tech-Report-Updated

Years ago i had a set of docs
it was most of what i had found Jan and Frits and others wrote about different topics. Mainly from KB pitlane and some other other dutch forums
It was lost in a lightning strike destroyed a computer and the back up. a few years back i might see if i can recover it.

I think i might have shared it with others?

[wobbly]

Having done hundreds of sims for differing engine projects, one of the many " trends " I have noted is that in a reed engine, especially anything that runs to high rpm's
is that as you increase the case volume, the petals need to be made thinner, thus lowering their 1st Mode Natural Frequency.
This then reaches a point where, even with effective curved stopper plates, the petals loose control and go spastic - smashing into the stops and bouncing off them.
In a sim, running the Inlet dialogue , you can see the tip lift being erratic from one run iteration to the next.
When this happens power drops at that rpm.

The CCR for a reed seems to be limited to about 1.3 - that gives enough volume for the pipe to draw from, and also allows petals thick enough not to go out of control.
But many larger displacement cylinders like a value slightly larger than this ie a smaller case.

EDIT - I have just read the spec sheet above and the Rotary Valve timing is well different from what Frits has given us at 152.5/90. Closing at 88 is the lowest number I have ever seen quoted.

[speedpro]

Off topic but I had a bit of a chat with SS90 at the 2026 NZ Grand Prix meeting 3&4 Jan at Ruapuna. Not who I expected at all.

[Rudex]

Wob/Frits

Can you say me what is the sense of using Bushing Bearing Modena KZ kk1? and if it would be better to use plastic insert in whole case (around the crank too) or like kk1?.
Why didn't they just machine the crankcase?

https://www.mondokart.com/10015-square_large_default/bushing-bearing-52-x-56-x-147-modena-kz.jpg
https://i.ibb.co/mVKk32CZ/kk1-case.png (https://ibb.co/LXym3czj)

Regards

[JanBros]

if the bearring gets lose in the case, you don't have to buy a new expensive crankcase, but simply change the inexpensive bushing ?

[Frits Overmars]

You have wrote far more and we are greatfull for everpart thats just little what a quick search turned up.
That last translated part i had never seen before? I never had a chance to read it. My own german is limited to what was in comics.
looks like it was indeed translated from something your wrote in 2009 translated using google and posted by RN? 2019?
Ignition Curves Copyright 2009 Friits Overmars - (translated via google translate and some manual editing RN Jan-201999
here is another verson
looks closer to english
https://opensimspark.org/_media/fos-ignition-curves-eng.pdf
Yes, that last version, translated with Deepl, does look more like the king's English; not bad at all.
In case you wish to compare it to the original text and at the same time brush up your German a bit:

[katinas]

the petals need to be made thinner, thus lowering their 1st Mode Natural Frequency.
This then reaches a point where, even with effective curved stopper plates, the petals loose control and go spastic - smashing into the stops and bouncing off them.


Just add illustration of your words for more clear imagination of what might be happening with the reeds (free oscillating) .

[flyonly]

54 x 54 twin port cylinder underway. Rear disc valve this one, this is for Vinduro so is 125cc.
This same setup ( bottom end) with a smaller cylinder could well be my next Bucket engine, after what, thirty odd years.

What is the plan to drive the disc?


Sent from my iPhone using Tapatalk

[husaberg]

Yes, that last version, translated with Deepl, does look more like the king's English; not bad at all.
In case you wish to compare it to the original text and at the same time brush up your German a bit:
Cheers everyday is a school day. But i struggle enough with English.


The CCR for a reed seems to be limited to about 1.3 - that gives enough volume for the pipe to draw from, and also allows petals thick enough not to go out of control.
But many larger displacement cylinders like a value slightly larger than this ie a smaller case.
.

In my search the other day i had seen a reference Frits had made ot the size of he reed valve Derbi case or the Rumi (i was skimming sorry)
Frits referenced it as being i think (if i recall correctly) as being quite a bit larger than the RSA.
i will have a look later an put it in. here...
looks like i asked the question ....

Would that not relate only to a disk valve? I have often seen it mentioned the optimum Crankcase volume would be smaller on a Crankcase reed. but i have never seen a definitive figure.
If you or Jan recalls what were the volumes on the Rumi and the Derbi reed valve. I realise that you may not have the figures available......but a a rough guide would be helpful


Frits Overmars esquire The Aprilia RSA125 has a TDC crankcase volume of 675 cc. That gives a primary compression ratio of 675 / (675 - 125) = 1,23. Rather different from your value....

I remember Jan saying that the crankcase volume of the Derbi reed valve engine was even larger than that of the rotary engine. And after Jan had laid his hands on it, that reed valve engine was the strongest 125 cc reed valver ever.
You see, the volumes of the transfer ducts and the volumes between the crank wheels and inside the piston are largely equal, and the volume of the reed cavity is a lot larger than the volume of a rotary inlet duct.



but your post and looking though an old collection of 1990s stuff i seen an old Boyseen 2 stage reeds packet (i had kept an it listed the reed number on the back for all sorts of bikes so you could cross reference )
357705357706


i got me thinking did those old 2 stage reeds do anything and do they work in such a situation.
They were successful in separating my money from my wallet and the stickers impressing passers by....

did they work in the old days and could they wok on say a VFoorce set up as anyone tried them in a modern reed valve?

[Flettner]

What is the plan to drive the disc?


Sent from my iPhone using Tapatalk

Don't know yet. Initially I was looking at the twisted tooth belt system, but over Christmas I've had a massive clean up of my workshop and have found a nice little set of helical right angle gears. So maybe that with a drive gear running off the top of the clutch gear.

[flyonly]

Don't know yet. Initially I was looking at the twisted tooth belt system, but over Christmas I've had a massive clean up of my workshop and have found a nice little set of helical right angle gears. So maybe that with a drive gear running off the top of the clutch gear.

Have you decided on the diameter. I am interested in doing something similar but would need to be twisted belt


Sent from my iPhone using Tapatalk

[Flettner]

Have you decided on the diameter. I am interested in doing something similar but would need to be twisted belt


Sent from my iPhone using Tapatalk

I have a large disc, spare out of my 360cc engine, that Ill use. It is all going to fit into a TF Suzuki 125 engine (farmbike) , most probably have to cast a new case to accommodate this disc drive.

[Flettner]

140 dia, plus small angle drive, hardened teeth.
Disc still to be cut to the appropriate timing.

[lodgernz]

If I were to channel my inner "wobbly" and attempt to throw down a hand at 'long distance troubleshooting roullette'
My first question is, why so cold, Batman?
Targetting 470c with the pipe design???
That should be ~600c if you want to make real power.
Only achieving a derived (not directly measured with high speed EGT probe....) 340c?
Re-running the pipe design for 340c would NOT be my first advice.
I would first wonder why your pipe is so cold to begin with, assuming it truly is.
The most likely culprit from a general theory perspective would be the tailpipt outlet diameter. Often termed "D_restrictor" in some pipe formulas....
If you have the exact diameter in your pipe on the bike from the formula you used, and you are that far under the formulas target EGT, I would have questions about the engine actually meeting the input parameters that went into the pipe calculator, or the pipe calculator itself, is it the FOS formula?
You should be closer to 600c EGT for an incredibly general ideal.
Being cold either means you are not delivering the heat energy that the calculator assumes you would have been delivering to the pipe or the tailpipe diameter on your actual pipe is larger than the calculator actually spit out.
Taking the tailpipe restrictor diameter smaller WILL increase the pipes EGT, and if you are currently "too large", making it smaller WILL bring with it an increase in power up until the point where you go "too small" and you burn holes in your piston, so there is a balance point to be found, and the pipe formula wont give you the EXACT perfect number for your engine. It SHOULD give you a generally safe place to START, and you tune it from there.
Generally speaking shrinking the tailpipe diameter is going to increase the EGT.
Inreasing the EGT will increase the net temperature of the pipe.
Increasing the temperature of the pipe will make the speed of sound within it FASTER.
Faster speed of sound = faster wave travel.
Faster wave travel = pipes natural "resonant frequency" goes up.
Well look at that:
1. You pipe is too cold (not metting the formula number).
2. Your pipe is peaking at too low an RPM (resoanant frequency LOWER than formula number).
So, logic says:
Make the pipe hotter (decrease tailpipe restrictor diameter) and you will see an attendent increase in pipe resonant frequency, maybe even landing exactly where the formula said you would be once you actually achieve the 470c EGT you entered into the formula.

This pipe was the sixth I have made for this bike, and my temperature assumption for it was based on similar experiences with previous pipes.
The tailpipe de Laval nozzle ID in this pipe is 14.0mm. Frits's formula for the nozzle ID, based on a crank HP of 16, is 12.4mm. This seemed too small to me, but I agree that making it smaller than 14 is the first step.
I'll fit a 13.0mm nozzle and do some more dyno runs. I suspect that a higher EGT will show the Lt of this pipe to then be too short.

Wos has also suggested that EO 192⁰ is a bit conservative. Maybe I need to raise that a little as well.

Thank you both for your advice.

[wobbly]

LODGER - I see a few things that have set you off on a dead end tangent.
You say you used an EGT of 470* - this is completely erroneous.
Any engine with that number in the header is about as well tuned as a weed eater.

All of the pipe compute programs are using the BULK AVERAGE PIPE TEMP, including the cooler duct, and this is in the range of 550* to around 625* dependent upon the fuel quality.
This gives an average speed of sound of 560 to 610m/s, thus a pipe average wall temp of around 425*C to 450*C at peak, and the EGT as measured in the header well into the 600*'s.
Quit working in the dark, even after a ton of carrots, IMHO it is absolutely impossible to do any meaningful engine design work, let alone accurate track/dyno tuning without using a data logged or at the very least a max recall EGT gauge.

Also, if you are absolutely insistent on accelerated engine wear, and loosing Hp, carry on using Motul 800 @ 30:1, I wouldn't use that cats pee if it was free even @ 20:1 where you should be.

The Wobbly Duct info sheet also states a recommended cooled duct length @ 1.5 bore for a square engine, with the header entry @ 2X bore - you stated a cooled duct out to 2X bore, this is NFG
as the A/F out at 2X bore is never going to make it back into the cylinder due to the return wave, as the port is closing.

EDIT - again, taking a suggestion the 192* " is a bit conservative ". What the hell does that mean, what is the actual Blowdown STA, and what are the transfers doing. JanBros has a free , really good port calculator.
Quit working in the dark - free technology is at your fingertips.

[F5 Dave]

I bought a small electric weed eater for the wife. Only works on small stuff.

The Grass cutterer guy has progressed to doing our lawn with a weed eater as he's transferring from heavy lawn mowers as he's well past 80. He'll probably stop all together soon. Can't rely on the in-laws forever.

So where can I get a tuned weed eater? Sounds like it could make the mundane fun.
As long as it siezes occasionally and throws me to the turf. Roughly.

[Jan Van Hamme]

Also, if you are absolutely insistent on accelerated engine wear, and loosing Hp, carry on using Motul 800 @ 30:1, I wouldn't use that cats pee if it was free even @ 20:1 where you should be.



Yes, damn it, I've made the “right” choice again.
A few years ago, I bought a pack of 12 x 1 litre cans of Motul 800 road race oil because I thought it was very good oil.
It is unopened and waiting to be used when my motorbike is assembled.
Now, after reading that message, I won't be able to get rid of that “cat's piss” anymore. Does it really cause so much wear and tear that I'd better not use it?


Translated with DeepL.com (free version)

[F5 Dave]

Works great in my trials bike.

[Jan Van Hamme]

In case you wish to compare it to the original text and at the same time brush up your German a bit:

Hi Frits,
I had already saved and printed your text on ignition curves for later use.
Now, in order to find and compile an optimal ignition curve, with your text in mind, I ran a simulation (in turbulent mode) in Engmod2T for every half degree of advanced ignition across the entire rev range.
So 8° fully from 3000 rpm to 9700 rpm.
8.5° fully from 3000 rpm to 9700 rpm....
up to and including 28° fully from 3000 rpm to 9700 rpm.

When I combine all the highest horsepower values per half degree in a curve, I get a strange ignition curve.
Namely, a flat curve of 15.5° over a large part of the rev range.
Could that be useful in practice?

Regards,
Jan

[Wos]

LODGER - I see a few things that have set you off on a dead end tangent.
You say you used an EGT of 470* - this is completely erroneous.
Any engine with that number in the header is about as well tuned as a weed eater.

All of the pipe compute programs are using the BULK AVERAGE PIPE TEMP, including the cooler duct, and this is in the range of 550* to around 625* dependent upon the fuel quality.
This gives an average speed of sound of 560 to 610m/s, thus a pipe average wall temp of around 425*C to 450*C at peak, and the EGT as measured in the header well into the 600*'s.
Quit working in the dark, even after a ton of carrots, IMHO it is absolutely impossible to do any meaningful engine design work, let alone accurate track/dyno tuning without using a data logged or at the very least a max recall EGT gauge.

Also, if you are absolutely insistent on accelerated engine wear, and loosing Hp, carry on using Motul 800 @ 30:1, I wouldn't use that cats pee if it was free even @ 20:1 where you should be.

The Wobbly Duct info sheet also states a recommended cooled duct length @ 1.5 bore for a square engine, with the header entry @ 2X bore - you stated a cooled duct out to 2X bore, this is NFG
as the A/F out at 2X bore is never going to make it back into the cylinder due to the return wave, as the port is closing.

EDIT - again, taking a suggestion the 192* " is a bit conservative ". What the hell does that mean, what is the actual Blowdown STA, and what are the transfers doing. JanBros has a free , really good port calculator.
Quit working in the dark - free technology is at your fingertips.


Dear Wobb,

For sure i am not experienced in diffrent 2 T Oils like you.
We run motul 800 in 8 h race liedolsheim where the best 50cc bikes have about 20 hp13000 and reving over 15000. Mix is 1:25

Which negative experience do you have with the french cats pee:wings: :laugh: :niceone:

Which oil would you adive for pump gas 98 mixture ? :niceone:


Thanks a lot

:niceone: every little step forward is a part of the puzzle ��

Grüße! Wolfgang

[Frits Overmars]

I ran a simulation (in turbulent mode) in Engmod2T for every half degree of advanced ignition across the entire rev range. So 8° fully from 3000 rpm to 9700 rpm. 8.5° fully from 3000 rpm to 9700 rpm.... up to and including 28° fully from 3000 rpm to 9700 rpm.
When I combine all the highest horsepower values per half degree in a curve, I get a strange ignition curve. Namely, a flat curve of 15.5° over a large part of the rev range.
Could that be useful in practice?
Jan, I dropped my crystal ball, so I don't know anything about your engine. I assume it's a two-stroke, but I'm not even sure about that. That's not much to base an opinion on...

[Jan Van Hamme]

Jan, I dropped my crystal ball, so I don't know anything about your engine. I assume it's a two-stroke, but I'm not even sure about that. That's not much to base an opinion on...

Sorry Frits,
I didn't phrase my question clearly enough.
The ignition curves for 2-stroke engines that I see here and there always start low in degrees, then rise steeply to +/-30 degrees and then drop back down at the start of the power band. Around max hp and rpm to 15° and from there further down.

What I mean is, an almost flat curve of 15.5° is very different from the usual curve shape I describe above. Would that still be useful in practice?
My engine... See attached screenshots.

[wobbly]

Wos, I made a post a few pages back about oils and the results I got in a quite extensive dyno test session.
The customer wanted to choose a replacement for R30, they had been running for years at 16:1.

The short story was that at high EGT numbers ( 650*C+) the oils I tested at 30:1, 25:1, 20:1 and 16:1 all made more power going down to 20:1 but no more at 16:1
Two oils made more power than the R30, these were HTX 909 and Maxima 927.
I tested several fully synthetic oils and none got close to the two oils above, and Motul 800 was the worst.
During the testing I decided to check what was occurring with the Motul and did some extended running - and discovered that the piston skirt wear was dramatically worse than the semi synthetic castor mix oils.
It was easy to measure as the wear was double, the clearance as new was exactly 0.002" ( the customer wanted Imperial numbers, as that is what he was honing to ) after1 Hr of hard running the Motul was 0.003"
where as the Maxima was 0.0025".

This result confirmed what I had read in the well known DynoTech publication ( Snowmobile guys with a real good Superflow dyno setup ).
They did alot of oil tests as well, and the technical issue is that when run at very high temps the Synthetic breaks down into its component chemicals, none of which are actual lubricants.
The Castor based oils when overheated, they break down at a lower oil film strength, but the component parts still lubricate very well.
Many 4T experts rubbish the Timken/Falex oil test rig, saying its not realistically representing what happens in a running engine.
But the rig results mirror exactly what happens in a 2T - Synthetics can have 10X the film strength of a Castor based oil, but the instant the film is broken the surfaces get physically torn up badly.
The Castor film fails much earlyer, but the wear pattern on the test drum is dead smooth.

Thus since that result I have been using Vrooam on track, and Maxima 927 on the dyno in the KZ engines , both semi synthetics, where we see 685*C EGT when running 110 octane.
The Vrooam is very clean, and hardly gives piston maps at all, but that is irrelevant when using EGT to get within one jet size of deto every run session.


HTX 909 will separate out of AvGas in about 1/2 Hr, but it and the others have no issues in 98 pump gas.

F5 - of course Motul 800 is just fine in a trials bike, not much more high temp loading then a weed eater.

EDIT, the other pointer I have is that I rebuild many KZ cranks, all after the same logged run time. The cranks run on full synthetic oils, have much of the silver coating worn off the cage and washer wear surfaces.
The Vrooam cranks still look like brand new.

[lodgernz]

LODGER - I see a few things that have set you off on a dead end tangent.
You say you used an EGT of 470* - this is completely erroneous.
Any engine with that number in the header is about as well tuned as a weed eater.

All of the pipe compute programs are using the BULK AVERAGE PIPE TEMP, including the cooler duct, and this is in the range of 550* to around 625* dependent upon the fuel quality.
This gives an average speed of sound of 560 to 610m/s, thus a pipe average wall temp of around 425*C to 450*C at peak, and the EGT as measured in the header well into the 600*'s.
Quit working in the dark, even after a ton of carrots, IMHO it is absolutely impossible to do any meaningful engine design work, let alone accurate track/dyno tuning without using a data logged or at the very least a max recall EGT gauge.

Also, if you are absolutely insistent on accelerated engine wear, and loosing Hp, carry on using Motul 800 @ 30:1, I wouldn't use that cats pee if it was free even @ 20:1 where you should be.

The Wobbly Duct info sheet also states a recommended cooled duct length @ 1.5 bore for a square engine, with the header entry @ 2X bore - you stated a cooled duct out to 2X bore, this is NFG
as the A/F out at 2X bore is never going to make it back into the cylinder due to the return wave, as the port is closing.

EDIT - again, taking a suggestion the 192* " is a bit conservative ". What the hell does that mean, what is the actual Blowdown STA, and what are the transfers doing. JanBros has a free , really good port calculator.
Quit working in the dark - free technology is at your fingertips.

Thank you again Wobbly. Let me address your points please:

1. I used the term EGT erroneously, I really meant the bulk average pipe temp

2. I take your point re the Motul 800. I used to run 25:1 but changed to 30:1 recently. I'll go to 20:1, or change to a better oil. I remember you said the Motul Kart oil is better?

3. I missed the advice to cool the port only to 1.5 x bore, so will fix that. The engine is close to square at 39.5 x 41.4

4. EO is 192°, blowdown angle-area is 2932⁰-mm2. This is 45% of the optimal angle-area recommended by Frits for 50cc and 13500RPM, based on the Aprilia RS125.

5. Transfers are as close as I can get to all of yours and Frits's axial and radial specifications, with angle-area of 28241⁰-mm2. A transfers duration 126°

6. I'll think about getting an EGT probe from Exhaust Gas Technologies. Which of their probes is best for bikes?

[wobbly]

Lodger - glad you get the point about the pipe temps.
The Motul Kart GP is a full synthetic, and suffers the same big end cage/washers wear as the others.
Depending upon who will give you a good price , any of the castor based oils I mentioned work just fine.
HTX 909 was used by Aprilia, we use Vrooam in KZ as its CIK approved and is very clean as I said.
But I use Maxima 927 on the dyno as it is one of the few oils that does not suffer from chrome bore streaking when running in.

I would still get JanBros port calculator as it works really well if you dont want the expense and drama of learning EngMod 2T.

The Stinger exposed tip probes are the best, and have a 2 year guarantee - I've sold and used literally a hundred of the things, never had a failure.

Gauge wise the best bet is to talk to the Kart shop guys, there are plenty of Mychron 4 - 2T( two temp inputs ) around as everyone has gone for the 5 version, that does the same logging but uses GPS
and Bluetooth, not " better " just easier.

[diesel pig]

Very interesting about the 2T oil's.
So just to make sure I understood what you are saying.
Use either
Maxima 927
HTX 909
Vrooam Caster based
Use whichever one is easier for one to get a hold of?

I would just like to back what was said about Exhaust Gas Technologies exposed tip probes. My one has ever given no problems since I have had it.

[lodgernz]

Lodger - glad you get the point about the pipe temps.
The Motul Kart GP is a full synthetic, and suffers the same big end cage/washers wear as the others.
Depending upon who will give you a good price , any of the castor based oils I mentioned work just fine.
HTX 909 was used by Aprilia, we use Vrooam in KZ as its CIK approved and is very clean as I said.
But I use Maxima 927 on the dyno as it is one of the few oils that does not suffer from chrome bore streaking when running in.


Thanks again Wobbly. I seem to be saying that a lot lately.

From your oil related post above, I gather that Vrooam Factory Racing 2T Kart oil is fine with 98, with no separation or carb deposits.
Would you still recommend 20:1 for this oil in a Bucket??

[reefmuncher]

Not sure if my comment was missed, was wondering if anyone had experience with the effect of axial and radial of the additional "boost" ports have around the C port on many smaller capacity Spanish and Italian race cylinders? The axial angles can be quite different between brands as seen in the image with DEA, Bidalot and Voca. 357724

Appreciate any thoughts on the subject.

[diesel pig]

That picture of the water cooled DEA cylinder fed reed. Got me all excited hoping it might be for a bored and stroked 50cc that would perfect to revitalize the Honda H100 engines I have in the rafters of my shed. But no they are for a 150cc vespa.

[wobbly]

So just to reiterate, yea all of the castor based oils work fine in pump gas, and yea they all make more power at 20:1.
Buckets , whatever, are no different.

[Mike Fisher]

I've just looked at Vrooam, is it the Factory or the Castor Blend you recommend, both seem to be descibed as having castor and synthetic components? I presently run Rock Oil Kart 100 which is a castor synthetic blend formulated for air cooled motors at 20:1 in a 370 Bultaco Astro used for short track, mainly 300m ovals. https://rockoil.co.uk/products/castor-kart-100/ I aim to gear to 9500rpm and to keep CHT under the plug washer to 215C.
Going right back to Gordon Jennings, in 1978, he ran tests on a PE250 that showed a power increse upto 15:1 with R40 thta is available here: https://vintagesleds.com/library/manuals/misc/jennings/oilpremix.pdf

[Frits Overmars]

The ignition curves for 2-stroke engines that I see here and there always start low in degrees, then rise steeply to +/-30 degrees and then drop back down at the start of the power band. Around max hp and rpm to 15° and from there further down. An almost flat curve of 15.5° is very different from the usual curve shape I describe above. Would that still be useful in practice?Indeed, most ignition curves start with their timing close to TDC to avoid kickbacks or even running backwards when starting. Then they switch to as much as 30° before TDC in order to have a lengthy expansion phase between end of combustion and exhaust opening, so the exhaust gases have lost most of their energy by the time they enter the pipe. That way the pipe cannot mess up the scavenging quite so much at revs that are too low for its layout.
But there are other options. Yes, at 2/3 the rpm of max.torque all pipe pulses arrive too early, messing up the scavenging. But what happens even lower in the rpm band?
At 1/2 the rpm of max.torque both the suction pulse and the stuffing pulse arrive back at the cylinder before BDC. But after this, the exhaust port is still open for a long time, so a secondary suction pulse and a secondary stuffing pulse can still manage to arrive at the cylinder before the exhaust port closes. And these secondary pulses can do some good, so it may not hurt to keep some energy in the exhaust gases at these low revs, i.e. start combustion closer to the 15° before TDC-region.
This still does not answer the question about your flat-line ignition curve. I did notice one thing about it though: the burn duration in your EngMod screenshots is extremely short....

[Jan Van Hamme]

Indeed, most ignition curves start with their timing close to TDC to avoid kickbacks or even running backwards when starting. Then they switch to as much as 30° before TDC in order to have a lengthy expansion phase between end of combustion and exhaust opening, so the exhaust gases have lost most of their energy by the time they enter the pipe. That way the pipe cannot mess up the scavenging quite so much at revs that are too low for its layout.
But there are other options. Yes, at 2/3 the rpm of max.torque all pipe pulses arrive too early, messing up the scavenging. But what happens even lower in the rpm band?
At 1/2 the rpm of max.torque both the suction pulse and the stuffing pulse arrive back at the cylinder before BDC. But after this, the exhaust port is still open for a long time, so a secondary suction pulse and a secondary stuffing pulse can still manage to arrive at the cylinder before the exhaust port closes. And these secondary pulses can do some good, so it may not hurt to keep some energy in the exhaust gases at these low revs, i.e. start combustion closer to the 15° before TDC-region.
This still does not answer the question about your flat-line ignition curve. I did notice one thing about it though: the burn duration in your EngMod screenshots is extremely short....

Those duration values are my fault.
I will have engmod generate the vibe and combustion parameters itself and then enter all these calculated values and repeat the entire process of searching for max hp per +0.5 degrees.

[Wos]

So just to reiterate, yea all of the castor based oils work fine in pump gas, and yea they all make more power at 20:1.
Buckets , whatever, are no different.

Wobb!!

Soory... christmas days i read not verry carefully

Thank you so much for repeading!!!
Sounds the parts will lif very much longer:cool::2thumbsup


What are the diffreces in reading the spark plugs?
Castor blends readable?

Recogniced that motul variates from black to light grey colors when others, for example ravenol fullsynth ester do variations in brown...

Merci!! ��

Wolfgang

[wobbly]

Mike F - its the Factory version of Vrooam, I have not tested the other type as its not available here.
I really just don't get why you, with plenty of experience and intellect , tell me you are attempting to tune with a CHT, that tells you absolutely nothing except how hot the plug washer actually is.
As I have said a 1000 times EGT tells you exactly the state of combustion, and allows incredibly simple tuning for peak power with any Density Altitude to within 1 jet of deto, in any engine.
In the tests I did I started with a baseline of R40 at 16:1 as per Jennings, but the modern castor based mixes made more power with less oil at 20:1.

Re the ignition curve testing - when off the pipe the scavenging efficiency is crap so the combustible mixture is full of residuals thus the burn speed is much lower as is power.
With a bunch of advance this gives time to at least use what energy is in the fuel that is available, and the biggest upside is that throttle response is hugely improved.
Further up into the powerband a similar but reduced version of the same effect is in play, but then we have the downside of increasing losses due to compressing the rising pressure from the increasing burn speed,
thus less advance is needed.

The whole idea of advance manipulation is as Frits described, plus as the combustion " cleans up " then the point of maximum cylinder pressure needs to trend toward 15* ATDC for peak effective use
of the rising pressure pushing on the piston.
The other side of that coin is the optimum crossover of burn duration Vs compressing losses is 15* BTDC that we all know is where most well tuned ( ie the correct compression ratio for the fuel ) engines end up at peak power.

We have the exact scenario being asked about in the KZ engines, with a flat line ignition set at about 17* BTDC in stock form.
This requires a very short pipe ( 760mm ), as there is way to much advance past peak power.
When these engines are retuned for road racing say, then the pipe reverts to the normal 800 mm TL, and the ignition , that is now adjustable, does the normal 30* dropping to 15* at peak, then down to 10 or so in the overev.
This gives a huge increase in power everywhere ( peak power much the same ) - except if a bigger carb is added.

Wos, see my remarks to Mike above, I refuse to answer any questions re tuning by looking at plugs or pistons - except the burn line on fine wire ground electrodes, but even then the ignition timing
should have been well established on the dyno, long before looking at plugs at the track.

[Jan Van Hamme]

I did notice one thing about it though: the burn duration in your EngMod screenshots is extremely short....
I think that a fast combustion time achieved by the high squish speed, the 55% squish band and the transfer scavenging angles used is not a bad thing?
When I let Engmod generate the combustion parameters, those duration values are back in the same range as before.
I hope that i can assume that my Zeeltronic PDCI-15V with 100 mJ spark energy en high energy Zeeltronic coil ZK3550 can still pull the spark in that "gust of wind"?

[wobbly]

JVH, the issue with " high" MSV is that this is analogous to adding advance due to the increase in flame speed, but to prevent deto you have to pull timing out.
What is " high " - and I am suspicious of any build that has 55% SAR.

[Wos]

Called Maxima !!!:niceone:
We are so exited wobb... how maxima:scratch::lol: smells:drool::lol:

[Jan Van Hamme]

JVH, the issue with " high" MSV is that this is analogous to adding advance due to the increase in flame speed, but to prevent deto you have to pull timing out.
What is " high " - and I am suspicious of any build that has 55% SAR.
Wobbly,
How I arrived at that 55%:
I set the ignition to 15° at maximum HP engine speed.
I selected the stinger diameter at which the MACH value in the nozzle is around 0.9.
Then I set the compression so that there is no detonation.
And to get msv to 40m/s, I had to go up to 55% squishband.

I don't know how strong that "high" energy coil is myself. The term ‘high energy’ is on the packaging, but that doesn't really say much.
Perhaps those of you with extensive knowledge of materials and product experience know what that type is capable of.

[husaberg]

Hi is logging in issue with Neels (vannik) (https://vannik.co.za/About.htm) sorted?

[wobbly]

Just sent an email to Neels.

[wobbly]

The answer is NO, wtf is going on - how hard can this be.

[wobbly]

JVH, the 40m/s is perfect, but can you not achieve this with 50% and less gap ?
Mach 0.9 is a little too high, ie stinger is too small, I believe there would be more power with 0.8 Mach and more compression or added timing.

[Wos]

JVH, the 40m/s is perfect, but can you not achieve this with 50% and less gap ?
Mach 0.9 is a little too high, ie stinger is too small, I believe there would be more power with 0.8 Mach and more compression or added timing.


So my conclusion is

If AF Ratio is ok/Sound, squish area set to 50%, gap for 40 squish velocity at peak power, lengt of pipe fits to peak, restrictor too...and so on:sweatdrop... did i forget something...i am sure:brick: ��

Then ....The only correct advance should be 15 degree at (about ) peak power??? ��

Experts? ;)



Let us continue fellows :drinkup:

Thanks! Wolfgang

[wobbly]

WOS, 15* BTDC is an optimum advance number that occurs when the static compression plus the dynamic compression created by the Delivery Ratio and the Trapping Efficiency combine
to reduce the pumping losses of compressing that retained charge, and if it all works together the peak cylinder pressure occurs near 15* ATDC.
If you can get away with more advance then one or both of the compression cycles is sub optimum.
Having to retard the ignition, leads to the opposite conclusion.

[husaberg]

Just sent an email to Neels.


The answer is NO, wtf is going on - how hard can this be.

might i suggest as many users as possible on ask the same question (respectfully) in this thread) worth a crack?https://www.kiwibiker.co.nz/forums/showthread.php/190561-IP-issue?p=1131243035#post1131243035

[Wos]

WOS, 15* BTDC is an optimum advance number that occurs when the static compression plus the dynamic compression created by the Delivery Ratio and the Trapping Efficiency combine
to reduce the pumping losses of compressing that retained charge, and if it all works together the peak cylinder pressure occurs near 15* ATDC.
If you can get away with more advance then one or both of the compression cycles is sub optimum.
Having to retard the ignition, leads to the opposite conclusion.

Thanks for detailed explanation Wobb! :niceone::niceone:

[Jan Van Hamme]

Deleted post

[husaberg]

Just sent an email to Neels.
KB's top dog has replied for Neels to try now.

[Vannik]

might i suggest as many users as possible on ask the same question (respectfully) in this thread) worth a crack?https://www.kiwibiker.co.nz/forums/showthread.php/190561-IP-issue?p=1131243035#post1131243035

After more than a month I am back! Wow, talk about serious withdrawal symptoms.

[Jan Van Hamme]

After more than a month I am back! Wow, talk about serious withdrawal symptoms.
Welcome back, Neels. I am delighted to be able to read your contribution once again.


@Wobbly, Mach 0.8 and 51% gives less power when I simulate it. What I have also found is that when Engmod generates a fospipe on my engine, it results in a stinger diameter that causes a Mach of 1.
And that Mach 1 does not cause any detonation in the fos exhaust or in my own exhaust.
I think something is wrong and will send a pack file to you and Neels.

[F5 Dave]

Thanks for making the effort. And for Spank for sorting the issue. It must be hard for amateurs to cope with odd issues.

[Peter1962]

After more than a month I am back! Wow, talk about serious withdrawal symptoms.

Great news ! Welcome back, Vannik. :wings:

[wobbly]

JVH, having Mach in the stinger nozzle means that tube is sonic choked. ie it is impossible for more flow to happen - talk to GPT about this.
If its not getting into deto, then that simply means the TubMax is very safely low.
IMHO, with a bigger stinger @ 0.8 Mach ( plus with MSV @ 40m/s ) and way more compression to push the TubMax up near the deto limit , it will make alot more power.
The only question to ask is will the new squish configuration cause piston clipping - I doubt it, as for example Jan has said the RSA didnt hit at 0.4mm/14000 rpm.

I did ask sarcastically " how hard can it be " - what was the actual problem with Neels access here?

[Jan Van Hamme]

JVH, having Mach in the stinger nozzle means that tube is sonic choked. ie it is impossible for more flow to happen - talk to GPT about this.
If its not getting into deto, then that simply means the TubMax is very safely low.
IMHO, with a bigger stinger @ 0.8 Mach ( plus with MSV @ 40m/s ) and way more compression to push the TubMax up near the deto limit , it will make alot more power.
The only question to ask is will the new squish configuration cause piston clipping - I doubt it, as for example Jan has said the RSA didnt hit at 0.4mm/14000 rpm.

I did ask sarcastically " how hard can it be " - what was the actual problem with Neels access here?
Wobbly, Msv 40m/s
Squishband 50%
Compression 12.7
Stinger mach1
Squish 0,65mm
Stroke 57mm
Tubmax 960
Deto @ Tubmax 970
Thanks that you will look at it over the weekend.

[Frits Overmars]

having Mach in the stinger nozzle means that tube is sonic choked. ie it is impossible for more flow to happen...In sonic choked flow, lowering the pressure downstream of the throat will not increase the flow velocity past Mach 1, and neither will raising the pressure upstream of the throat.
But raising the upstream pressure will increase the gas density and thus the mass flow, even if the throat velocity remains Mach 1.
One more pedantic point: Mach 1 flow in the stinger may not be Mach 1 all of the time. The practical limit of Mach 0,8 may be an average value derived from practical experience and your Mach 0,8 flow guideline may contain instants of Mach 1. But we must proceed with caution there; Mach 1 all of the time will be risky.

[wobbly]

Here is a stinger nozzle Mach trace at peak power.
In this and all the other cases I have simulated if 0.8 Mach is exceeded it means ignition or compression has to be reduced to some unexpectedly low value
as the retained pipe pressure is overly excessive.
The peak velocity is occurring as the main wave descends down the rear cone and enters the stinger - this plot is logged 1/2 way along a 25mm long nozzle.
Subsequent peaks and troughs, are reflections and superpositions off atmosphere, the nozzle entry and the step up to the main stinger tube, I assume.
I do not know if going sonic creates a shock wave at the nozzle entry - maybe Neels can enlighten me/us.

[ApolloMotoMoto]

After more than a month I am back! Wow, talk about serious withdrawal symptoms.

Welcome back, Neels!

:D

[ApolloMotoMoto]

Wobbly, Msv 40m/s
Squishband 50%
Compression 12.7
Stinger mach1
Squish 0,65mm
Stroke 57mm
Tubmax 960
Deto @ Tubmax 970
Thanks that you will look at it over the weekend.

0.65mm squish???

Come on man, what are you afraid of?

:D

0.01 x stroke is nearly guaranteed safe from clipping.

So, going larger than 0.57mm squish is just giving up MSV potential for no good reason at all.

Strong caveat that this number "40m/s MSV" is more of an imperical tuning symbiote that has been discovered over COUNTLESS engine examples...

But, from having attempting this same game myself, you are going to make sacrifices "trying to find" 40 MSV when you fully enforce all of the statoe of the art design guidance as Wobbly has clearly laid out.

Its NOT easy to get there, the CR being high enough to get your TubMax into the "making power" region is limiting the MSV somewhat, higher CR = lower MSV for all other geometries being equal; the compression is "resisting" the acceleration of the squish event.

So, maybe you have been limiting CR to sneak out some extra MSV, but as Wobbly has correctly pointed out, now your TubMax falls into the toilet and your doing weed-eater stuff.

You need to use ALL of your available "squish gap" potential, period. Or you WILL be leaving power on the table.

0.65mm squish with 57mm stroke is just screaming "but WHY though???" to my eye.

The aprilia RSA is ~54mm stroke.

Wayne just gave you the key reference;


"The only question to ask is will the new squish configuration cause piston clipping - I doubt it, as for example Jan has said the RSA didnt hit at 0.4mm/14000 rpm."

54mm stroke and they could safely use 0.4mm up to 14k.

To scale that to your 57mm;

0.4 / 54 = 0.0074 squish gap per mm stroke

57 x 0.0074 = 0.42mm

I suggest you plug 0.42 squish gap in and see how much easier it gets to achieve that 40 MSV with useful compression; and you shouldn't need near 55% SAR to do it ;)

[Jan Van Hamme]

0.65mm squish???

Come on man, what are you afraid of?

:D

0.01 x stroke is nearly guaranteed safe from clipping.

So, going larger than 0.57mm squish is just giving up MSV potential for no good reason at all.

ApolloMotoMoto,
The reason why I thought not to go too small with the squish is the following:


A 125RSA has a squish gap of 0.7mm
It could well be that the crankshaft is made of 15NiCr13.
The bearings in which it rotates are BC1-1442-B cylindrical roller bearings (found in the datasheet by Jan Thiel & Frits Overmars)


My crankshaft is from a Yamaha DT200. (I don't know what material it is made of from the factory).
I have to press the crankshaft apart and back together.
The bearings are ball bearings.
I suspect that the distance between the two bearings (support points) on a DT200 crankshaft is greater than on a 125RSA.


Although the piston speed is much lower in my application than in an RSA, I thought that with much lower crankshaft rigidity, a lower steel alloy, and less stable ball bearings... I should be cautious about the squish distance.
There is someone working behind the scenes for me, for which I am extremely grateful, who has a wealth of experience that could fill an Olympic swimming pool...I have now also heard that it may be less and that there would be no contact between the piston and the head. I am waiting patiently.

Thank you for your insights and help. I am just a private individual, not a competitive rider or anything... but I am a 2-stroke enthusiast at heart.
Jan

[ApolloMotoMoto]

ApolloMotoMoto,
The reason why I thought not to go too small with the squish is the following:


A 125RSA has a squish gap of 0.7mm

Jan

You super sure about that? ;)

It was a MotoGP engine, and the squish gap IS a "tunable feature" of the engine. Are you super confident that everytime the RSA125's rolled off the paddock they did so set to 0.7mm squish gap???

I will repeat that Wayne shared a rather large clue, and if you do the deep dive (husaberg where are you!) this has been discussed probably 10-20 times over the course of this thread; what squish gaps WERE actually used in racing, what was tested on the track but never really "raced" and what was tested on the dyno. I can assure you it was not a static single numer over the entire racing pedigree of the engine.

I can absolutely assure you that no matter how "inadequate" your crankshafts are, they PALE in comparison to what I am playing with.

I build and tune "80cc Motorized Bicycle Engine Kit" engines from such fine makers as Jilin-Zeda Technology Corporation, Runtime Products, and Zong Dong Freight Corportation (not joking).

It is made with Chinese "cough" equivalent to something like SCM440, called CR40.

The videos you see on facebook of the fine manufacturing conditions that you will find in a shop with dirt floors, you can start to understand what I am working with.

I am certainly not running them as they come "out of the box" :D, and with correct preperation, mostly a good press fit and well trued, I am running my 42mm stroke at 0.30mm squish gap without clipping at 15k RPM's.


I totally understand your hesitation in theory, but in practice your concern is actually unfounded (especially if your piston speed is significantly lower than the RSA), and you are leaving a key piece of the Rosetta Stone un-leveraged because of it.

[Jan Van Hamme]

You super sure about that? ;)
.
No, I'm not sure about that at all. That's just what I read and found in a datasheet.
I also have no idea how a racing engine is tuned when it goes on the track or on the test bench.
There are people with tons of experience and knowledge that far exceed mine, and there are also probably a lot of falsehoods to be found here and there on forums.
It's not easy to always make the right synthesis that would then be the correct one.
At the end of the day, I really value the practical experience and approach of those who have already proven themselves.
After all, the world doesn't revolve around just pressing the run button on a 5-axis CNC machine.

[Niels Abildgaard]

You super sure about that? ;)

I
I can absolutely assure you that no matter how "inadequate" your crankshafts are, they PALE in comparison to what I am playing with.

I build and tune "80cc Motorized Bicycle Engine Kit" engines from such fine makers as Jilin-Zeda Technology Corporation, Runtime Products, and Zong Dong Freight Corportation (not joking).

It is made with Chinese "cough" equivalent to something like SCM440, called CR40.

The videos you see on facebook of the fine manufacturing conditions that you will find in a shop with dirt floors, you can start to understand what I am working with.

I am certainly not running them as they come "out of the box" :D, and with correct preperation, mostly a good press fit and well trued, I am running my 42mm stroke at 0.30mm squish gap without clipping at 15k RPM's.




Sounds interesting.Have You put pictures somewhere?

[ApolloMotoMoto]

Sounds interesting.Have You put pictures somewhere?

Yea I think I can find a few ;)

[Niels Abildgaard]

Yea I think I can find a few ;)


Very interesting.
How much is each engine ab China and how much modification is allowed in this class?
Can we have a picture of bike with engine?

[wobbly]

Here is my understanding of the issue - mostly from the usual on line conjecture.
Jan stated he had tested the RSA to 14,000 with 0.4mm gap and had no problem.
The engine, as delivered, was at 0,6.
Many team engineers at the track increased that to 0.7 as it was easier to tune and rev'd slightly harder.

Even with a crap crank and bearings, a 57 stroke at 9500 is a million miles away from clipping.
Here are the numbers I have 14:1, on E10 Unleaded, 0.6mm/50% = 40.8m/s , 9500 = 18m/s - safe as hell.

[ApolloMotoMoto]

Very interesting.
How much is each engine ab China and how much modification is allowed in this class?
Can we have a picture of bike with engine?


I'll see what I can dig up...


The "motorized bicycle" engine kits are ~$200 a piece to start with ;)

There are many classes that allow various levels of modification;

There is the ChinaGirl "Series":

ChinaGirl SuperStock class for unmodified engines.

ChinaGirl SuperSport class allowing intake/ exhaust/ head/ ignition modification, by no internal engine mods.

ChinaGirl Superbike class allowing essentially ANY modification a person can dream up within a given displacement limit of 90cc, but it must utilize the stock Chinese cast carnkcases and cylinders (modification of these parts is allowed, just no "custom" cast/CNC crankcases or cylinders).

And, there is the "Formula" Series:

Formula 2 allowing for any SINGLE SPEED/DIRECT DRIVE configuration of air cooled 2-stroke engine design to compete with a displacement limit of 100cc.

Formula 1 allowing for any SINGLE SPEED/DIRECT DRIVE configuration of water or air cooled 2 stroke engine design to compete with a displacement limit of 125cc.

CNC crankcases allowed, ANY cylinder from any source that meets the requirements allowed.

There are NO fuel rules.

As of yet there are no "elecronics restrictions", anything you can dream up through electronic/digital controls is allowed until something shows up that requires regulation.

[Frits Overmars]

Jan stated he had tested the RSA to 14,000 with 0.4mm gap and had no problem.
Many team engineers at the track increased that to 0.7 as it was easier to tune and rev'd slightly harder.46 years ago I was investigating the lower squish gap limit for the grandfather of the RSA, the Rotax 124. I ran it to 14.000 rpm with 0,4 mm squish gap and had no problem either (a well-set up RSA even revs to 14.500 rpm without problems).
Increasing the squish gap reduces the squish velocity and the combustion speed, raises the EGT and increases overrev, which in some circumstances can make life easier for the rider, even if it costs power. So that is what these team mechanics did.

We may need to define 'crap bearings'. The ball bearings in the Rotax 124 and the roller bearings in the Aprilia RSW and RSA are fine. The Aprilias with their 54,5 mm stroke ran a piston speed of 26,3 m/s at 14.500 rpm with 0,4 mm squish gap without problems.
But when I was searching the squish gap limit for the Rotax 124, I also had a 50cc Kreidler with its typical angular contact crankshaft ball bearings on the dyno.
The Kreidler with its 39,7 mm stroke, a much lighter piston and a piston speed of only 21,2 m/s at 16.000 rpm required a squish gap of at least 0,7 mm because those bearings allowed much more crankshaft flex. Crap bearings? They ran very light but shimming them was a pain and you cannot get away with the squish that roller bearings allow.

[F5 Dave]

Ahh thanks, my Suzuki 50 i set up as 0.5mm. I was running 2 base gasket and all was well. But if I reused the base gaskets twice the piston would tickle the head. 15mm pin from memory. I started running bigger pin and yamaha rod. Never thought to see if a stronger crank assembly could take closer squish.

[Vannik]

Thanks for making the effort. And for Spank for sorting the issue. It must be hard for amateurs to cope with odd issues.

Seems I am only halfway back, I can get access from work but still not from home. And work has nothing to do with 2T engines so not really good to access from here.

Who do I contact about sorting it out all the way?

[husaberg]

Seems I am only halfway back, I can get access from work but still not from home. And work has nothing to do with 2T engines so not really good to access from here.

Who do I contact about sorting it out all the way?

Ask here.
https://www.kiwibiker.co.nz/forums/showthread.php/190561-IP-issue?p=1131243035#post1131243035
preferably quote Spankme. (thats not a joke)
https://www.kiwibiker.co.nz/forums/showthread.php/190561-IP-issue?p=1131243055#post1131243055

[Niels Abildgaard]

I'll see what I can dig up...


The "motorized bicycle" engine kits are ~$200 a piece to start with ;)

There are many classes that allow various levels of modification;

There is the ChinaGirl "Series":

ChinaGirl SuperStock class for unmodified engines.

ChinaGirl SuperSport class allowing intake/ exhaust/ head/ ignition modification, by no internal engine mods.

ChinaGirl Superbike class allowing essentially ANY modification a person can dream up within a given displacement limit of 90cc, but it must utilize the stock Chinese cast carnkcases and cylinders (modification of these parts is allowed, just no "custom" cast/CNC crankcases or cylinders).

And, there is the "Formula" Series:

Formula 2 allowing for any SINGLE SPEED/DIRECT DRIVE configuration of air cooled 2-stroke engine design to compete with a displacement limit of 100cc.

Formula 1 allowing for any SINGLE SPEED/DIRECT DRIVE configuration of water or air cooled 2 stroke engine design to compete with a displacement limit of 125cc.

CNC crankcases allowed, ANY cylinder from any source that meets the requirements allowed.

There are NO fuel rules.

As of yet there are no "elecronics restrictions", anything you can dream up through electronic/digital controls is allowed until something shows up that requires regulation.

Thank You for pictures and explanation.
Sounds lot of fun for reasonable funds.

[F5 Dave]

No. It's obviously totally ridiculous.

Fortunately I like totally ridiculous :woohoo:

[Vannik]

Ask here.
https://www.kiwibiker.co.nz/forums/showthread.php/190561-IP-issue?p=1131243035#post1131243035
preferably quote Spankme. (thats not a joke)
https://www.kiwibiker.co.nz/forums/showthread.php/190561-IP-issue?p=1131243055#post1131243055

Thank you, I have done so.

[Vannik]

Thank you, I have done so.

Connected from home for the first time since mid November!

[ApolloMotoMoto]

Connected from home for the first time since mid November!

Hoooray! Now its a "proper" homecoming ;)

[TZ350]

357773

Was pretty happy with the way the Suzuki RG50 rotary valve conversion is going.

The moth holes into the crankcase will get sealed up with some J-B Weld.

357774

Everything was a neet fit.

357775

RG50, rotary valve and 26mm carburettor.

Rotary Valve Suzuki RG50

[diesel pig]

I take it those are GP100/125 rotary valve parts? How are you going to drive the rotary valve between the carrier and the crankshaft? Are you going to sacrifice the taper part of a RG50 stator flywheel?

[TZ350]

I take it those are GP100/125 rotary valve parts? How are you going to drive the rotary valve between the carrier and the crankshaft? Are you going the sacrifice the taper part of a RG50 stator flywheel?

357782 RG50 crankcase

Yes, Suzuki GP100/125 rotary valve parts.

357780 AM6

This is an AM6 crank but the approach is the same with a RG50 one.

The long stroke AM6 crank and 95mm rod paired with an oversized cylinder can give you a 100 plus water cooled CC's in a light weight engine.

20mm sleeve and step on the trigger to support the RV hub.

The old flywheel hub is turned down to form the ignition trigger.

The trigger does not have to be pulled up tight on the taper.

The alloy cup pulls up against the end of the crank and just gently presses the trigger onto its taper so that it all comes apart again easily.

The direction of crank rotation naturally tightens the nut holding the trigger.

The crush from the "O" ring on the trigger is all that is needed to clamp the RV hub.

5mm pin in the crank to drive the RV hub.

357781 AM6

The RG50 crank is a bit longer than the AM6 so needs the thread cut off the RG and a 6mm thread tapped in to hold the trigger in place.

The RG crankcases without the crankcase reed and long rod leves an enormous cavity. No idea how much but there must be a lot more relative crankcase volume Than the Aprilia RSA125 had.

I figure, so long as a bit of mixture makes it upstairs to light the fire and get the pipe working, pipe resonance will take it from there. The greater the crankcase volume the more mixture the pipe can suck upstairs to the cylinder. Only works on RV engines, reed engines need some crankcase compression pressure to close the reeds after the suction stroke.

357783

To fit the RG50 crankcase in a NF4 frame we mill 30mm of the drive side mount after bogging up the inside with a bit of Knead-It. The full RV conversion takes about four of the big tubes.

Team ESE still have not made an 50cc engine that is good as the better Dutch efforts, but we live in hope.

Rotary Valve Suzuki RG50

[wobbly]

TeeZee, you are making some pretty wild assumptions, for no reason, as EngMod quickly tells you if an idea is sound or not.
You say you have more relative case volume than the Aprilia that had about a 1.23 ratio, and im sure with 100 people working in R&D that if a bigger case was better, it would have been tested and subsequently used in GP's
- why are you assuming bigger, is a better, if its never been tested in a controlled back to back.
But the sim will tell you immediately if bigger is better, and what the best timing's are for that setup.

And reed engines don't need " a smaller case volume to give some compression to close the reeds ", they need a smaller volume as going incrementally bigger requires thinner reeds to match the Helmholtz
of the case, and if its not done, this results in a power loss from the bigger case - not an increase.
Eventually the thinner reeds needed, then go spastic at high rpm, as they don't have sufficient stiffness to keep the harmonic frequencies under control.

This factor has resulted in the guide volume of about 1.3 ratio, much smaller than the Rotary Valve as used by Jan.
We are now getting much closer to the power of the Aprillia with reeds, and its not the smaller case fighting pipe suction to fill the cylinder that is the limiting factor.
As a 125 with a 1.3 ratio has a case volume of about 540cc, over 4X the cylinder displacement, how is that factor limiting what the pipe can pull up the transfer ducts.

[TZ350]

TeeZee, you are making some pretty wild assumptions, for no reason, as EngMod quickly tells you if an idea is sound or not.
You say you have more relative case volume than the Aprilia that had about a 1.23 ratio, and im sure with 100 people working in R&D that if a bigger case was better, it would have been tested and subsequently used in GP's - why are you assuming bigger, is a better, if its never been tested in a controlled back to back.

Somewhere back a bit Jan Thiel commented that he would have liked to have progressively tried more crankcase volume as he felt he was not at the limit yet and there was more power to be gained with more volume and studying crankcase flow. I guess he saw more volume as a good idea. Unfortunately he retired before he could. The people who took over corrected Jan's big crankcase volume mistake and were left wondering why the engine made less power.

I suspect EngMod2T as good as it is, is based on known good engines. We never got to see the ultimate RS125 and how big its crankcase volume would have been.

And also the volume I have is what I naturally get with the conversion I have done. Anything less would require crankcase stuffing. I don't have the labour available of a large workshop crew to make the incremental well documented back to back changes. Can't be bothered myself. It runs pretty good as is. Makes more power than any of the other 50's I have seen on this dyno. And yes you are right, Engmod2T would be a good guide but I would need to measure the actual crankcase volume. Again, at this point, for the moment I can't be bothered. Works well as is and for now I have other ideas to pursue. Engmode might be a good guide for my ideas about variable RV inlet timing.

[TZ350]

.

TeeZee, you are making some pretty wild assumptions, im sure with 100 people working in R&D .....

A 100 people working in R&D Oooh such luxury but alas there is only me and Cully ....

I have other ideas to pursue. Engmode would be a good guide for these ideas about variable RV inlet timing. But for now I will checkout if its even physically possible.

357784 357785

It looks like I can swing the outer cover 25 deg. Using a Power Valve servo.

The idea is at low RPM to move the cover against the direction of RV rotation. Here there will only be half the inlet tract in line with the crankcase.

At high RPM the cover would be moved in the direction of RV rotation and the full inlet tract will be open to the crankcase.

So, low RPM, half the inlet tract diameter exposed, Rotary valve timing. 155/65

High RPM, cover rotated 25 deg. Full diameter of inlet tract open. Later effective Rotary valve timing 130/90

This idea is based on a paper I read where it showed that after you have established the correct inlet duration you could move the duration (timing} to make best power at different RPM.

Not sure if I have got this right, I guess the R&D Dept will have to fluff around and find out.

Will have a look to see what Engmod has to say. But I am unsure how well it can cope with the discontinuity of the inlet tract. Might have to be another suck it and see experiment.

Rotary Valve Suzuki RG50

[wobbly]

My point was you dont need 100 people to see if a case volume change is worthwhile.
On my computer it takes well less than a minute to rerun a sim with a new case ratio.
I dont understand why you would actually build something with an unknown case ratio, when you can test it in minutes in the computer, thats what you paid the money for after all.

[husaberg]

357782 RG50 crankcase

Yes, Suzuki GP100/125 rotary valve parts.
AM6
.rats


Tin worm or Rats?
357786357787
section at top of pic of the valve?

[TZ350]

Tin worm or Rats? section at top of pic of the valve?

Good spotting. Overheating on an old motor from the valve rubbing on a slightly misaligned cover.

[TZ350]

TeeZee, you are making some pretty wild assumptions, for no reason, as EngMod quickly tells you if an idea is sound or not.
This factor has resulted in the guide volume of about 1.3 ratio, much smaller than the Rotary Valve as used by Jan.
We are now getting much closer to the power of the Aprillia with reeds, and its not the smaller case fighting pipe suction to fill the cylinder that is the limiting factor.
As a 125 with a 1.3 ratio has a case volume of about 540cc, over 4X the cylinder displacement, how is that factor limiting what the pipe can pull up the transfer ducts.

First off, let's be clear, I think EngMod2T is a spectacularly good program for simulating conventional 2T engines. It's an essential tool for any 2T tuner of a conventional engine. But I think it is limited by the conventional engines its based on. It can't predict what it does not know.

Now for crankcase volume. Let's explore it with a thought experiment. A two stroke works better, the better you can flush the cylinder and the better trapping purity you achieve the better the results. So logically, if you flush fresh charge through the cylinder for three weeks and a day the purity of the trapped charge is going to be 100%.

This is impactable due to the time constraints at 15.000 rpm. But something about 4X is good and maybe a little more might be better. So oversized case volume that comes easily from this conversion is not such a dreadful thing. It would be hard work with this engine to achieve a 1.3 ratio by case stuffing all for possibly little or no real return. Certainly not going to loose sleep over it and I post my findings so that others don't too.

Granted, with big case volumes there may be other issues like resonance in other ducts and the pipe. But a big case volume, bigger than 1.3 ratio does not look like the end of the earth for a RV engine.

There is also issues with managing a team of a 100 R&D types, group think and the personal preferences and the qualities of the leader. A Japanese Factory's GP development team stuck with 56/50 bore stroke for a long time while getting their noses wiped by the 50/50 team from another factory. If the 56/50 team had of had EnginMod2T they probably would have got past that blind spot quicker.

[wobbly]

I was never suggesting 1.3 was better, we know its not, but we know 1.23 is better for a Rotary Valve as its been done.
Your thinking says 1.2 or something is better, but have nothing to back up that theory.
Here is the RSA125 with a bigger case - sure as hell doesnt work on that engine with pretty much the accepted limit timings ( for the 250 ) of 91.5/142.5

Edit - Yamaha stuck with the 56/50.6 engine with the 3YL/4DP as it was based on the TZR case that was a current road bike. Kosinski and Harada won 250GP titles during that time with special factory only
stacked double crank, square , rotary valve TZM's. But it was obviously corporate policy at the time to utilise the road bike cases, nothing to do with short sightedness or lack of knowledge.
They went square in 2000 with the NX5 and won with Jaques on the 250, but those race only cases were sand cast and have had nothing but issues with main tunnels wearing out in no time.

[TZ350]

Your thinking says 1.2 or something is better, but have nothing to back up that theory.

My thinking is all about not being to hung up.

My experience with work on the Team ESE dyno. Is if it is difficult to achieve the ideal. A larger case volume on a RV engine than the currently accepted value is not the end of the earth, and that might be valuable re assurance for someone.

Wob, thank you for your insights.

[TZ350]

.
Repairing the moth holes in the crankcase.

357789 357790 357791

Sand away some of the inner RV plate.

Mask with sellotape.

Cover with J-B Weld epoxy steel resin.

Rotary Valve Suzuki RG50

[F5 Dave]

TZ, are you going to see Yamaha rod to get those revs without smoking the poor RG crank?


Just got handed a spare Classic racer magazine on Sunday. Haven't opened it but it has OJ's 2000(?) 250 Yamaha on the front.
Closest we saw it at Philip Island was moving or other side f track from pits, so quite looking forward to the article.

[TZ350]

TZ, are you going to see Yamaha rod to get those revs without smoking the poor RG crank?

AM6 rod kit.

There are a couple of these rotary valve Suzuki RG50 engine conversions in the works. Two 50cc another, possibly a turbo 70 or an 85. We have also found ways to get 110 cc's out of one of these. If the 110 materialises and works. We will take it to Christchurch for the next Battle of the Buckets.

357792

Basic AM6 stuff is pretty affordable of Aliexpress.

357794

After transfering the RG50 primary gear. GN125 clutches can be made to fit as well. Stay tuned for details.

357795

Also GN125 clutch spring kits can work wonders for a standard RG50 clutch.

Rotary Valve Suzuki RG50

[Vannik]

I suspect EngMod2T as good as it is, is based on known good engines. We never got to see the ultimate RS125 and how big its crankcase volume would have been.


EngMod2T and 4T is not based on any engine but on thermodynamics and gasdynamics. Any shortcomings is from my lack of programming skills and/ or misunderstanding the physics. And from modeling combustion and scavenging as quasi-dimensional and not full 3D.

[F5 Dave]

I just usedDT175 springs and TS plates allowed 4rather than 3. But 100 power may unravel that.

[TZ350]

EngMod2T and 4T is not based on any engine but on thermodynamics and gasdynamics.

Good to know, thanks. I knew it was good and now understand why.


I just used TS plates allowed 4 rather than 3.

Yes, I remember you sharing that info. We have been doing that ever after you clued us in.

[Noxin]

Many team engineers at the track increased that to 0.7 as it was easier to tune and rev'd slightly harder.


What was the main effect that simplified the tune and harder rev?
Was it the lowered compression ratio or the squish gap itself?

[wobbly]

Increasing the squish gap, decreases the MSV. Small changes have quite significant effect on this parameter.
In the RSW going from 0.6 to 0.7mm gives a change of 48M/s to 42M/s = 12.5%

Lowering the MSV is analogous to retarding the ignition timing, as the reduction in the speed of the turbulent eddies exiting from the squish annulus ( curtain area )
reduces the flame fronts burn speed thru the chamber - also with the upside of decreasing the losses due to compressing the trapped mixture later.
Retarding the timing or reducing the MSV, thus has the mixture burning later in the cycle, and this puts less heat into the piston and more heat into the pipe.

There is a minor effect from reducing the static compression ratio, and this has similar effects as the reduction in MSV - more heat into the pipe
As far as tuning goes the lower com and reduced flame speed allows higher egt numbers without getting into deto, giving a higher bulk gas temp and thus increased wave front speed thru the pipe = more overev power.

[TZ350]

Some posts on crankcase volume.

https://www.kiwibiker.co.nz/forums/images/misc/quote_icon.png Originally Posted by Frits Overmars https://www.kiwibiker.co.nz/forums/images/buttons/viewpost-right.png (https://www.kiwibiker.co.nz/forums/showthread.php?p=1130253001#post1130253001)
In order to take full benefit of a large crankcase volume you need free-flowing transfer ducts. That means: large cross sections, short gas column lengths and large time.areas.

https://www.kiwibiker.co.nz/forums/images/misc/quote_icon.png Originally Posted by Frits Overmars https://www.kiwibiker.co.nz/forums/images/buttons/viewpost-right.png (https://www.kiwibiker.co.nz/forums/showthread.php?p=1130330060#post1130330060)
An Aprilia RSW125 has a TDC crankcase volume of 650 cc. An RSA125 has 675 cc and a bit more power. See where this is going?

https://www.kiwibiker.co.nz/forums/images/misc/quote_icon.png Originally Posted by Frits Overmars https://www.kiwibiker.co.nz/forums/images/buttons/viewpost-right.png (https://www.kiwibiker.co.nz/forums/showthread.php?p=1130500811#post1130500811)
Increasing the crankcase volume has several consequences. One of those is that the flow through the carb will be more even, less violent, which usually results in a leaner mixture.

https://www.kiwibiker.co.nz/forums/images/misc/quote_icon.png Originally Posted by Frits Overmars https://www.kiwibiker.co.nz/forums/images/buttons/viewpost-right.png (https://www.kiwibiker.co.nz/forums/showthread.php?p=1130549426#post1130549426)
make sure your crankcase volume is not too small. I have seen lots of cases with too little volume, but none with too much yet. The optimum primary compression ratio is probably less than 1.3.

https://www.kiwibiker.co.nz/forums/images/misc/quote_icon.png Originally Posted by wobbly https://www.kiwibiker.co.nz/forums/images/buttons/viewpost-right.png (https://www.kiwibiker.co.nz/forums/showthread.php?p=1130549579#post1130549579)
In my testing I have found no more power going to a bigger than 1.3 case on a reed engine.
This is a function I believe of the efficiency of the rotary valve intake system being able to better fill the case at high rpm,using the 1.24 as Frits has described , but having said that I have only just crept over 50 Hp with a 125 reed, and the Aprilia RV made alot more than that, so maybe a huge case simply isnt needed at the lower bmep.

https://www.kiwibiker.co.nz/forums/images/misc/quote_icon.png Originally Posted by Frits Overmars https://www.kiwibiker.co.nz/forums/images/buttons/viewpost-right.png (https://www.kiwibiker.co.nz/forums/showthread.php?p=1130852554#post1130852554)
Off the pipe you need a pump with the minimum amount of dead volume; on the pipe you'll want the engine to breathe directly from open air (mixed with a bit of fuel and oil). But that oil has to pass through the crankcase to keep the bearings happy. Hence my 24/7-setup

https://www.kiwibiker.co.nz/forums/images/misc/quote_icon.png Originally Posted by wobbly https://www.kiwibiker.co.nz/forums/images/buttons/viewpost-right.png (https://www.kiwibiker.co.nz/forums/showthread.php?p=1130852561#post1130852561)
There are several issues involved with the reed engine and its case volume - that has effects not seen in an RV setup. The bigger the case the less are the pressure swings from piston movement and the pipe action ( assuming the same depression at the Ex port created by the pipe ) around BDC.

This changes the tuned frequency of the case vol, but this also requires thinner reeds to get them open fast and far enough. Of course changing the reed stiffness then changes the intake tuned frequency,they then hit the reed stops and flutter uncontrollably - and so it goes on and on.

I tried machining the KZ10B case back to make the volume smaller as I already had the 5mm laser cut spacer from a test making the case bigger by pushing the reed block outward. This failed miserably, so of course you then go the other way - this also failed,but only partially in that I did not then try differing reeds to compensate as I should have.

Adding a spacer behind the reed block HAS NOTHING to do with the intake length, this is already as short as it can be, with the rubber manifold recessed into the reed stuffer.

All I can say is that from a huge amount of sims and real world reed engine testing, that a very well tuned engine with good power capability ( bmep ) likes the case down near 1.3.

An engine with less power ( bmep ) capability ( for whatever reason ) tends to respond better to the case closer to 1.4.
When you are making 8 Bar and or 14 Bar BMEP of course these exceptions to the norm tend to prove the rule of thumb.

https://www.kiwibiker.co.nz/forums/images/misc/quote_icon.png Originally Posted by Frits Overmars https://www.kiwibiker.co.nz/forums/images/buttons/viewpost-right.png (https://www.kiwibiker.co.nz/forums/showthread.php?p=1130330850#post1130330850)
The smaller crank will give the pipe more crankcase volume to breathe from. This larger volume will also lower the resonance frequency of the inlet system, hence the drop at high rpm. It can be compensated with a shorter inlet tract, a bigger carb diameter and a later inlet closure. To put it real simple: if you have more volume, you need more time to fill it. But more time, i.e. later closure, has adverse effects at low revs. So my preference is a shorter tract (unless you go the 24/7-way and employ a reed for the low revs, and swing it out of the way at high revs).

https://www.kiwibiker.co.nz/forums/images/misc/quote_icon.png Originally Posted by Frits Overmars https://www.kiwibiker.co.nz/forums/images/buttons/viewpost-right.png (https://www.kiwibiker.co.nz/forums/showthread.php?p=1130803955#post1130803955)
crankcase compression ratio = TDC-volume / BDC-volume
TDC-volume = 680 cc (I'll take your word for it)
BDC-volume = TDC-volume - cylinder volume
cylinder volume = 173,7 cc
BDC-volume = 680 - 173,7 = 506,3 cc
crankcase compression ratio = 680 / 506,3 = 1,343
And now for some reverse engineering:
what TDC-volume will give a crankcase compression ratio of 1,43?
TDC-volume = comp.ratio / (comp.ratio - 1) * cylinder volume
TDC-volume = 1,43 / 0,43 * 173,7 = 577,7 cc.


Some of the posts where I came away from with the idea that bigger was better for rotary valve crankcase volume.

I found the EngMod2T section where crankcase compression ratio is calculated.

357799

I have a case volume of 120cc on my rotary valve 50. So will try a series of simulations using 1.4, 1.3, 1.2, 1.15, 1.1 and see where it goes.

Wob favors 1.23, I have great faith in EngMod so it will be interesting. Give me a bit of time to develop the Simulation for the current 50 and run it. When the engine is together we will put it on the dyno.

[wobbly]

Its not that I favour 1.23 - that's just what has been proven in the RSA, and when I ran bigger in the sim of that engine, you can see it lost considerable power everywhere.

120cc in a 50cc engine is insanely small @ 1.69 CCR
Getting to 1.2 CCR will need 264cc under the piston - obviously screaming out for a long rod and plenty of crank clearance in the case.

I see no point in going up as small as 1.3, as that is guaranteed to loose power - Jan has been there done that when he changed from a 115 rod to a 120.
You don't need to use the calculation page for CCR - simply put in the cc or the ratio in the engine dialogue page and the code does the rest, just be sure to invoke the " include the transfers " radio button.

Regarding testing your rotating valve cover idea, the code will deal with a step in area at the end of the manifold, exactly as it deals with a step or discontinuity in the pipe
where the manifold bolts on.
It cannot know the step is asymmetric, but that is taken care of reasonably well with the changes in timing you will enter.
The pipe step functionality is well proven to represent reality, even when those steps are just 1/2 moon's at the top and bottom of the duct exit - its the area change that is the overriding feature
in modelling the effects.

Neels has done alot of work recently on updating the functionality of the Rotary Valve inlet modelling, so you will benefit from that immediately.

[TZ350]

120cc in a 50cc engine is insanely small @ 1.69 CCR Getting to 1.2 CCR will need 264cc under the piston -

My gestumit calculations of 120cc at bdc are obviously badly out. As is, this motor will have more crankcase volume than a standard RG50.

I will have to wait until the motor is assembled so I can do a proper liquid measurement. Thanks for your comments, very helpful.

Crankcase Compression Ratio
TDC-Volume / BDC-Volume
120 / 70 = 1.7
170 / 120 = 1.4
270 / 220 = 1.23 CCR

[TZ350]

.

Aligning up the primary drive gears. AM6 crank and RG50 clutch basket.

357801

First step is to cut the starter gear of the back of the RG50 clutch basket.

357802

The next step is drill the hub so it slides further onto the input shaft and then make a driving coller for it. I made this one out of an aneld engine sprocket.

357803

As everything has moved inboard. I made this basket for the clutch release bearing.

357804

All good. For a bigger engine you could use a GP/TF/TS five plate clutch. There is plenty of room under the Suzuki RG50's clutch cover.

Rotary Valve Suzuki RG50

[TZ350]

.

357805

This is what a really wild rotary valve looks like. Interestingly, on the dyno it started easily, made very good power, and even idled. Throttled well enough on the dyno but I was not game to try it on the track. I had heard the stories about the difficulties of tuning a late closing RV and was not keen to put the time into it. Another day maybe.

[F5 Dave]

Rob, just leaving the large area of Suzuki 1/2 case reed out will create a large area of mixture to the rear side of the case. I'd far prefer it in the transfer area where it can quickly be drawn into the cylinder. Gas will still need time to accelerate and move.

[TZ350]

.

Hi F5. Yes, lots of stagnant volume. Unsure about it myself. Latter plan is to have something removable to fill that void. Going to try to get sensible dyno results for comparison. But really good back to back tests that give some confidence seem hard to achieve in my experience but we will give it a go.

Currently trying to find some two stroke combination that makes up for the scarcity of up to date two stroke machinery available in NZ. Not many Derbi or Aprilia 50 engines around or even Aprilia 125's. Mostly last century Suzuki farm bike stuff.

[TZ350]

Crank stuffers? An Aprilia RSW125 has a TDC crankcase volume of 650 cc. An RSA125 has 675 cc and a bit more power. See where this is going?

My confidence about having greater crankcase volume was inspired by reading posts like this.

[TZ350]

.

357807 357808

Top end 110cc.

357809357810

Bottom End 180cc

Did the tests several times until I was confident about the numbers.

Crankcase Compression Ratio
TDC-Volume / BDC-Volume = Crankcase Compression Ratio.
290 / 240 = 1.2 CCR

Worked out much better than I was expecting ....... :woohoo:

So now I have a better figure to use in my EngMod2T simulation.

When I have the new engine together I will see if I can make an even more accurate measurement.

Rotary Valve Suzuki RG50

[wobbly]

The RSW Vs the RSA is not even a close apples for apples comparison regarding the physical layout and many other detail changes - I have serious difficulties attributing
the RSA power increase to simply 25cc of CCR = going from 1.238 to 1.227 = only 8/10ths of 1 % change.
That % would be 0.4 Hp in 54, sure, absolutely worth doing, along with at least 5 other changes with far more significance.
But the RSA had its own downsides - the rear valves gear drive, and the front mounted bent pipe that also negatively affected the bikes weight balance and thus its handling.
Jan has said that given the opportunity to do it again, he would far rather have a valve on each side, not one on the back.

[TZ350]

.

The Dutch are at 20RWHP with their 50's. This is where we are at now. Not even the best for NZ but we are working on it.

357814

This is someone else's but essentially the same motor as I am building. Hopefully with some direction from EngineMod2T we can do a bit better with our Rotary Valve Suzuki RG50 motors.

[Frits Overmars]

The Dutch are at 20RWHP with their 50's.In 2025 each FreeTech50 bike in the first start row had about 24 rear wheel HP.

[wobbly]

After wasting near on 5 years of his and our time building completely dumb off the wall shit on UTube, Alex is now running a pretty much conventional 50cc 2T
and is achieving 27HP at the sprocket on petrol for his Bonneville LSR project.
During this time I wasted a bunch of time arguing with him about CCR, as he originally had a reed inlet system and by shear chance had close to a 1.3 CCR ratio but then decided to suddenly change to a rotary valve.
As usual that initially made about as much power as a chainsaw, until he finally listened and changed the case to around 1.2 CCR in part by adding a heap of clearance around the crank.
I havnt commented since about his engine, as Im afraid he will go wildly off on another tangent, and automatically start thinking " bigger is better ".

It will be a very interesting and worthwhile exercise to model your rotary 50cc TeeZee in EngMod, try the CCR in increments, then see what happens with the dyno real world tests.
In that case, I dont think absolute power numbers are the goal at all, but seeing the trend will be very informative.

[pirkka1]

50cc power levels and dynos have been a HOT topic recently here Finland

<iframe width="560" height="315" src="https://www.youtube.com/embed/-mI_Xb-c04A?si=e-s1U69E93m5BAvW" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>

Do all commercial dynos have "Fudge" factors like dynojet?,and can 20+ Rear Wheel Horsepower be measured straight from the roller without fudge?
??

[wobbly]

Read this, explains it all.

http://www.factorypro.com/dyno/true1.html

[TZ350]

.
357815 357816

I have started setting up the engine part of the project in EngMod2T. The first simulation does not match the dyno results of my friends bike. Which has the same engine as the one I am building.
I will need to enter his pipe specs before things properly align. My friend has a 50cc high end Barakit pipe on his bike that we dynoed.
I have tried modeling the pipe without much success.

If anyone has a drawing for the 50cc high end Barakit pipe they could post. I would be very grateful.

I have graphed the EngMod2T output in kW as that sort of represents rwhp after transmission losses. The DynoJet graph is in std RWHP.

[TZ350]

In 2025 each FreeTech50 bike in the first start row had about 24 rear wheel HP.

I expect that at least some of the bikes on the front row have cylinders that the clever tuners have made themselves. Bikes on rows behind are probably sporting special aftermarket cylinders they have purchased.

There is a lot about FreeTech50 that is similar to F5 Buckets. Making your own cylinder is Ok and to be applauded but you need skills like Flettner's. In F5 Buckets you can't just buy your HP. You are expected to make your own from basic non competition engine parts. Excepting, Carb, Ignition, Piston Pipe and anything you can make yourself like a cylinder is unrestricted.

357817 357818

Not possessing Flettners skills I think my best rout is to convert a Suzuki RG50 to rotary valve so I can make use of a basic inexpensive cast iron version of the 50cc AM6 cylinders from China. There is nothing "race" about them other than some over excited advertising.

We have a few RG50 bottom ends but no good cylinders. We have worn them out ages ago and they are like rocking horse poo to replace. The best we ever achieved with them was 14 RWHP.

I am not expecting to break 20 RWHP any time soon. But it will be a lot of fun trying and not to expensive which is what Buckets is mostly about, fun and not being to expensive.

[Betaversio]

.
357815 357816

I have started setting up the engine part of the project in EngMod2T. The first simulation does not match the dyno results of my friends bike. Which has the same engine as the one I am building.
I will need to enter his pipe specs before things properly align. My friend has a 50cc high end Barakit pipe on his bike that we dynoed.
I have tried modeling the pipe without much success.

If anyone has a drawing for the 50cc high end Barakit pipe they could post. I would be very grateful.

I have graphed the EngMod2T output in kW as that sort of represents rwhp after transmission losses. The DynoJet graph is in std RWHP.

You have to try and model all mechanics (port and channel dimensions, compression ratios, timings, reed valves etc.) as precisely as possible. For cylinder ports, buy Vinamold to get flow widths correctly. Measuring pipe by hand is good practise, and you have to learn how to do it. It is part of simulator skill. In simulator, you need VERY precise dimensions for pipe to get it matching. You can measure pipe volume (using water) and check if it does match with calculated volume. I once tried to calibrate with 55 mm error in pipe length. It was not possible at all. After correct pipe calibration was somewhat correct after 5 runs. Use always turbulent model when doing calibration.

Vannik, if you happen to read this, does pipe volume number in EngMod mean only "pipe" volume or including exhaust channel also?

Then you have to set up combustion efficiency, transfer model and motor / pipe temperatures. By combustion efficiency you will scale BMEP value into correct number. By pipe temperature you will scale motor rpm into correct. And transfer model, avoid best models (RSW125) unless you have engine with very good scavenging. I have found that if transfer model is correct, then pipe temperatures are easy to calibrate. With wrong model it can be pain in the ass.

Re dyno graph: You need correct engine power to calibrate with. Without precisely known added value in your dyno I would probably just assume that your Dynojet rwhp equals somewhat real engine hp. I have not used Dynojet, so all info I know is in link that wobbly posted some hours ago.

Re simu graph: While showing simulator graphs, just show simulator graph. It does show engine power and it is ok, no need to try to quess some rwhp at that point.

And then, go and convert this dynojet graph in paper to .pou file using Post2T. Then you can overlap these in Post2T when doing calibration runs and it is easy to compare.

-A

[TZ350]

.


Use always turbulent model when doing calibration.

357819 Yes, turbulent mode gives a different result all right.

[Vannik]

Vannik, if you happen to read this, does pipe volume number in EngMod mean only "pipe" volume or including exhaust channel also?


The exhaust port duct volume is included.

[pirkka1]

Read this, explains it all.

http://www.factorypro.com/dyno/true1.html

Thanks, that pretty much confirms our experience.
Our small CC(50-125~) tuning community has now 5 DIY inertia dynos that i know of, mine being the latest, and we have always used/referred to using "True RWHP". I dynoed a 2017 bone stock KTM 300 EXC (with a 17" street tire)at ~37Hp for example.
357821
Some have brake dynos but i dont think they are easily compared due to differing load,losses and temps etc.
Most are running free GSF-dyno software,one Simpledyno and one PEREK Dyno controller. all of them showing pretty much within 1hp in 14 so 7% of eachother tested side by side. but 20-30~% less than commercial dynos.
Would for sure be fun to have a dutch 24whp bike visit one of our dynos, atleast just to see how far behind we are in development :D

[wobbly]

From having done many racebike sims and then having used a DynoJet to to test the project built directly off the sim result, the average loss from crank power, down to the roller
and thus including the built in fudge factor - is close to 14%.
The only different result was a 125 kart setup, with both rear wheels on the roller.
This would have had less tyre/wheel inertia, giving a higher dyno reading, in that case the loss was closer to 12%.
On my inertia engine dyno, with accurate inertia and the as measured dyno rolling friction, I get an 8% loss as measured at the gearbox sprocket - for the 125/50Hp
kart engines I test all the time.

The readings are accurate, as I tested 4 different engines when a new junior class was being researched for Kartsport NZ.
My results were all but identical to all of the manufacturers eddy current dyno results, run in sweep mode.
All the results are slightly different ( more accurate ) since loading the FOS weather correction factor, now available at my request in the latest Sport Devices software.

[TZ350]

.
I was unsure what the "Turbulent" setting in EngMod2T meant. Here is the answer from Google AI:-

In the context of EngMod2T (a two-stroke engine simulation software), "turbulent" refers to a modeling setting used to simulate chaotic, high-velocity gas flow, particularly within the cylinder and exhaust ports, rather than smooth (laminar) flow. <button jsuid="CNodhb_d" tabindex="0" data-amic="true" data-icl-uuid="f9c25b68-f5b1-48db-b271-d23fe31f1c56" aria-label="View related links" class="rBl3me" jsaction="click:&CNodhb_b|S9kKve;mouseenter:&CNodhb_b|sbHm2b;mouseleave:&CNodhb_b|Tx5Rb" data-wiz-attrbind="disabled=CNodhb_b/C5gNJc;aria-label=CNodhb_b/bOjMyf;class=CNodhb_b/UpSNec" data-ved="2ahUKEwipuJzc9cqSAxXRRmwGHWQqF9UQye0OegQIARAB" style="margin: 0px 6px 0px 0px; background-color: rgb(229, 237, 255); border-width: initial; border-style: none; border-color: initial; border-radius: 10px; height: 20px; padding: 0px; width: 20px; position: relative; outline: 0px; cursor: pointer;"><svg style="margin-top: 3px;" fill="currentColor" width="12px" height="12px" focusable="false" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"></svg>
</button>
Here is what "turbulent" means in EngMod2T:<button jsuid="CNodhb_i" tabindex="0" data-amic="true" data-icl-uuid="cc3eed44-0e0d-4fc1-90ba-6a672db039ba" aria-label="View related links" class="rBl3me" jsaction="click:&CNodhb_g|S9kKve;mouseenter:&CNodhb_g|sbHm2b;mouseleave:&CNodhb_g|Tx5Rb" data-wiz-attrbind="disabled=CNodhb_g/C5gNJc;aria-label=CNodhb_g/bOjMyf;class=CNodhb_g/UpSNec" data-ved="2ahUKEwipuJzc9cqSAxXRRmwGHWQqF9UQye0OegQIAhAB" style="margin: 0px 6px 0px 0px; background-color: rgb(229, 237, 255); border-width: initial; border-style: none; border-color: initial; border-radius: 10px; height: 20px; padding: 0px; width: 20px; position: relative; outline: 0px; cursor: pointer;"><svg style="margin-top: 3px;" fill="currentColor" width="12px" height="12px" focusable="false" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"></svg>
</button>


Combustion Modeling: EngMod2T allows for "Turbulent entrainment combustion," which uses turbulence modeling to calculate how air and fuel mix and burn within the combustion chamber.
Flow Modeling: Selecting "Turbulent" (usually the default) instead of "Laminar" tells the software to account for chaotic eddy formations, which is essential for accurate simulation of high-speed engine flows.
Performance Impact: Turbulent flow significantly impacts engine scavenging (how well exhaust is replaced by fresh charge). Proper turbulence modeling helps the software predict how flow separation occurs in the ports and how effectively the cylinder is purged.
Default State: Because most real-world engine scenarios involve high speeds, turbulent flow is the default setting for simulation. <button jsuid="CNodhb_y" tabindex="0" data-amic="true" data-icl-uuid="5b0eae1b-6e3c-4d4f-8d5e-659dd83b9534" aria-label="View related links" class="rBl3me" jsaction="click:&CNodhb_w|S9kKve;mouseenter:&CNodhb_w|sbHm2b;mouseleave:&CNodhb_w|Tx5Rb" data-wiz-attrbind="disabled=CNodhb_w/C5gNJc;aria-label=CNodhb_w/bOjMyf;class=CNodhb_w/UpSNec" data-ved="2ahUKEwipuJzc9cqSAxXRRmwGHWQqF9UQye0OegQIAxAE" style="margin: 0px 6px 0px 0px; background-color: rgb(229, 237, 255); border-width: initial; border-style: none; border-color: initial; border-radius: 10px; height: 20px; padding: 0px; width: 20px; position: relative; outline: 0px; cursor: pointer;"><svg style="margin-top: 3px;" fill="currentColor" width="12px" height="12px" focusable="false" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"></svg>
</button>

If a simulation is running too slowly, or if it is unclear whether the flow is laminar or turbulent, users might start with "laminar" to test, but true engine operation is almost always "turbulent".

[pete376403]

NZ company that offers directly coupled (car wheel hub or bike chain drive) dynos to eliminate all the variables of tyre adhesion, slip, etc. Located in Victoria St, Lower Hutt. While working for HP I did a (PC) service call there, security up the wazoo, they bought the PC and bits down to the lunchroom so as not to let me in the main office. They have some good testimonials for car and bike customers https://dynapack.com/

[diesel pig]

one of the very few reasons an Ignitech will not produce accurate ignition curves , is EMI. You MUST use resistor plugs and caps. The other issue is the proximity of the trigger or any other input/output
wiring to the coil charge wires.
They are on opposite ends of the loom plug for a reason.
I always run the coil wires on one side of the bike ( or whatever ) frame, and the triggers etc on the other side.
These simple things remove 99% of issues.
Also depin any unused loom wires, DONT coil them up to operate as very good antennae.

Thanks, Once again for pointing this out, I was just today moving a bike with a ignitech mounted on it, which I have been having ignition problems with for a while and I checked where the unshielded pick up coil wires are running. It is within 5mm of the Ignition coil. I think I now know why I was having problems.

[jamathi]

The RSW Vs the RSA is not even a close apples for apples comparison regarding the physical layout and many other detail changes - I have serious difficulties attributing
the RSA power increase to simply 25cc of CCR = going from 1.238 to 1.227 = only 8/10ths of 1 % change.
That % would be 0.4 Hp in 54, sure, absolutely worth doing, along with at least 5 other changes with far more significance.
But the RSA had its own downsides - the rear valves gear drive, and the front mounted bent pipe that also negatively affected the bikes weight balance and thus its handling.
Jan has said that given the opportunity to do it again, he would far rather have a valve on each side, not one on the back.

I did an ENGMOT-simulation with a disc on each side: no good.
The idea for the RSA came from the flowbench, I saw how much the conrod obstructed the flow.
The result somewhat disappointed me, but I still had some ideas about the internal flow in the crankcase.
But then I retired, and development went the wrong way.
I am still convinced that 60HP would have been possible. but instead a 'Honda-type' exhaust port was tried...........
How STUPID can you be: 3HP less............
I still don't understand this, after all the problems we had at DERBI, where ALL exhaust bridges broke...
We also saw that a bent pipe lost some power.
In the design phase I proposed having an insert in the crankcase, between cylinder and crankshaft so that experiments with in-crankcase flow, turning vanes and case-volume would be easy and quick, I am still regretting this was not done: it was the only way to reach 60HP... as the cylinder had reached its limit.....

[Betaversio]

From having done many racebike sims and then having used a DynoJet to to test the project built directly off the sim result, the average loss from crank power, down to the roller and thus including the built in fudge factor - is close to 14%.

I have to ask it. Including fudge factor: Dynojet reads 100 hp, then you put additional factor of 1.14 wich means 114hp from engine? And if we get fudge off, there is 80 hp real power in dyno roll?

[wobbly]

Jan , I have not looked into the twin rotary valve concept, and I should not assume anything about how Neels modelled this, but being a single dimensional model
I have doubts that the flow regime into the case itself can be replicated correctly ( whatever that may be ).
This is also affected by the fact that Neels has very recently updated the code to more accurately replicate the inlet duct extension, past the valve, and this has proved to give much better results.

Re the DynoJet numbers, all I can report is what my results were from many sims, and subsequent rear wheel Hp numbers.
So yes, I built a 485cc Banshee based racebike that made 102 RWHP, the sim said it was 58 Crank per cylinder.
Another 3YL/4DP TZ250 made 80 Hp on a Dynojet, the sim said 46/cylinder - so I can be pretty damn sure that when I finally fit the modified 3XV cylinders and new pipes where the sim says 55Hp/cylinder
that bike will read at around 95RWHP.

[husaberg]

Wasn't there multiple cnc set of case done not long after the the 2t were booted out of GP that took Aprilia cylinders
I can't recall what it was called but pretty sure it was Dutch and i have some pics...
edit
Dolf van der wood

https://www.kiwibiker.co.nz/forums/album.php?albumid=4862&attachmentid=304664
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=303497&d=1413067355https://www.kiwibiker.co.nz/forums/album.php?albumid=4862&attachmentid=304666
https://www.kiwibiker.co.nz/forums/album.php?albumid=4862&attachmentid=304666

[Frits Overmars]

Wasn't there multiple cnc set of case done not long after the the 2t were booted out of GP that took Aprilia cylinders. I can't recall what it was called but pretty sure it was Dutch and i have some pics...
edit Dolf van der wood
https://www.kiwibiker.co.nz/forums/album.php?albumid=4862&attachmentid=304664
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=303497&d=1413067355https://www.kiwibiker.co.nz/forums/album.php?albumid=4862&attachmentid=304666
https://www.kiwibiker.co.nz/forums/album.php?albumid=4862&attachmentid=304666Those were the twin-disk Aprilia cases, designed by my friend Dolph van der Woude, who also gave Aprilia their first 250cc GP win and who also designed the Aprilia 250cc V-twin, and produced by Thijs Hessels.
357825357826357824

[diesel pig]

Those were the twin-disk Aprilia cases, designed by my friend Dolph van der Woude, who also gave Aprilia their first 250cc GP win and who also designed the Aprilia 250cc V-twin, and produced by Thijs Hessels.
357825357826357824

If there is a flat disc cover at each end of the crankcase. How does the primary drive work? and of cause, do you know wither it was ever finished and ran?

[Frits Overmars]

If there is a flat disc cover at each end of the crankcase. How does the primary drive work? and of cause, do you know wither it was ever finished and ran?To the best of my knowledge it was never finished because the whole purpose was to built a better 125cc road racing engine. And this endeavour was killed off by the FIM decision to substitute the 125cc class with 250cc (cheaper, cleaner and more reliable, haha!) foulstrokes.
I do not feel at liberty to answer your other questions, except: ask yourself how you would drive the twin(!) balance shafts.

[diesel pig]

To the best of my knowledge it was never finished because the whole purpose was to built a better 125cc road racing engine. And this endeavour was killed off by the FIM decision to substitute the 125cc class with 250cc (cheaper, cleaner and more reliable, haha!) foulstrokes.
I do not feel at liberty to answer your other questions, except: ask yourself how you would drive the twin(!) balance shafts.

I am wondering if that boss of material above the gearbox housing and behind the flange the cylinder would mount on, Has something to do with it. A row of thin gears or chain down one side maybe? After that I am out of ideas.
I am thinking two sightly smaller carbs that equals a one large one would generate better carburation at low to midway slide openings maybe?

[husaberg]

I am wondering if that boss of material above the gearbox housing and behind the flange the cylinder would mount on, Has something to do with it. A row of thin gears or chain down one side maybe? After that I am out of ideas.
I am thinking two sightly smaller carbs that equals a one large one would generate better carburation at low to midway slide openings maybe?

https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130312865&highlight=exactweld#post1130312865

Jan had mentioned a long time ago he was plaining on starting with twin 34mm

https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1131030731&highlight=exactweld#post1131030731

In regards to the primary here is how the exactweld did it
https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130703351#post1130703351

[diesel pig]

I must say I am very interested in the twin disc set up as LangTuning are working on a twin intake (using reeds) right behind the A and B ports on each side. I am very keen to know how it performs. It may the start of something very interestly. Who knows? That seems to be the way with 2 strokes if one gos to far out side the box of currant knowledge. One just has to build it and see.

[Frits Overmars]

I must say I am very interested in the twin disc set up as LangTuning are working on a twin intake (using reeds) right behind the A and B ports on each side. I am very keen to know how it performs. It may the start of something very interestly. Who knows? That seems to be the way with 2 strokes if one gos to far out side the box of currant knowledge. One just has to build it and see.Here you go DP. The technical rules of Langtunings's 'TunerBattle 2026' specified 'inlet on the cylinder' , otherwise the reed valves would have found a place on the crankcase. The engine has a bore and stroke of 57mm x 56mm and produces 50 rear wheel-HP at 11600 rpm.
357830
Here is designer Kevin Lorenz explaining the how and why: https://www.youtube.com/watch?v=5bm7xMG0dSs
(https://www.youtube.com/watch?v=5bm7xMG0dSs)
357829
There's another video in the making showing the cylinder preparation. I will post it here as soon as it's ready.

Here you go:
https://www.youtube.com/watch?v=EoteWuwdAUw

[diesel pig]

The Germans are interesting,They are either must stick to the rules with no end to it or when they do leave the reservation things get interesting real fast

[diesel pig]

After watching that first video, some thoughts, The cylinder has first class exhaust ports and Transfer ports design. I take it the rules mean it must have Air cooling? otherwise if it had water cooling I think it would be even better.

[wobbly]

Is there an easy way to translate a whole .docx, maybe someone can post the 2026 Tunerbattle on here

[Frits Overmars]

Is there an easy way to translate a whole .docx, maybe someone can post the 2026 Tunerbattle on hereHere is the Tunerbattle 2026 rulebook Wob.
https://www.simsonforum.net/thread/82726-lt-tunerbattle-2026-regelwerk/

If you search for Langtuning Tunerbattle 2026 or Langtuning Wintertreffen 2026 you will find more info and videos.

I use DeepL (https://www.deepl.com/nl/translator) for translations and I understand they also offer an option to translate complete .docx files but that may be a paid option; I'm not sure.

By the way: you do know that Youtube offers realtime translation, don't you?
357832

As for the exhaust pipe on the Tunerbattle-winning bike: yes, it is fat. Now why is everybody looking at me? I was only there for the free bratwurst.
Anyway, to quote Crocodile Dundee: That's not a pipe. This is a pipe.
357831

[wobbly]

Here is the resident BRC Towel Head with his new RPG I did for the 500cc mini sprint dirt trackers.
I will let you know if the NSA is watching this.

[ken seeber]

Just saw this. It'd be interesting to test the depth:


https://hotmart.com/en/marketplace/products/e-book-master-in-two-stroke/X102278817J

[diesel pig]

Just saw this. It'd be interesting to test the depth:


https://hotmart.com/en/marketplace/products/e-book-master-in-two-stroke/X102278817J

It would depend on the translation from portuguese to english, I would think. Depending on that , it could be interesting.

[Peter1962]

It would depend on the translation from portuguese to english, I would think. Depending on that , it could be interesting.

The Yamaha DT 180 is a 45 year old engine, air cooled, cylinder reed intake low performance soft enduro engine made back then for the Brazilian market. Why choosing such a poor starting point when you want to write a book anno 2026 on high performance tuning on two strokes ? :confused:

Would it not make more sense to start with a modern MX 125 engine like the yamaha yz125, or the KTM 125 SX or the KTM 250-300 SX, which have a real life market share, are being produced by the tens of thousands per year and are not boutique projects ? And which are on the technological level that manufacturers produce in 2026 and not that of 1981 ? Or with the snow sled engines, where two stroke still has a dominating market position and there is still development ?

https://sledmagazine.com/two-stroke-engine-options-2026-snowmobiles/

Why not start from the best performing and most modern normaly aspirated sled engine, the Polaris 9R, designed in 2022 ? Or the most modern MX engine, the ktm 250-300 TBI SX-XC in its latest itteration that dates from one year ago ? Those are real market comparissons, the yam dt180 is a relic.

[JanBros]

you could go even further : why not start with an Aprilia RSA125 ?
it doesn't matter what your starting point is, what matters is that what he is saying works. what matters is using cheap-ass engines available to everyone and one can do the same and check that the writers results are correct. when proven right, aply the same theories to whatever you want.

[diesel pig]

The Yamaha DT 180 is a 45 year old engine, air cooled, cylinder reed intake low performance soft enduro engine made back then for the Brazilian market. Why choosing such a poor starting point when you want to write a book anno 2026 on high performance tuning on two strokes ? :confused:

Would it not make more sense to start with a modern MX 125 engine like the yamaha yz125, or the KTM 125 SX or the KTM 250-300 SX, which have a real life market share, are being produced by the tens of thousands per year and are not boutique projects ? And which are on the technological level that manufacturers produce in 2026 and not that of 1981 ? Or with the snow sled engines, where two stroke still has a dominating market position and there is still development ?

https://sledmagazine.com/two-stroke-engine-options-2026-snowmobiles/

Why not start from the best performing and most modern normaly aspirated sled engine, the Polaris 9R, designed in 2022 ? Or the most modern MX engine, the ktm 250-300 TBI SX-XC in its latest itteration that dates from one year ago ? Those are real market comparissons, the yam dt180 is a relic.

Well you maybe right, It would take someone getting it and having a look at it. It could be like Bell's book, none of the the current tuners say it is wrong just old. With old ways of doing things.

[ApolloMotoMoto]

Just saw this. It'd be interesting to test the depth:


https://hotmart.com/en/marketplace/products/e-book-master-in-two-stroke/X102278817J

There was a bit of a row on one of the facebook groups about the content of this book a few months back...

Apparently a large amount of Frits Overmars work is included without attribution or explicit permission; the entire FOS Leaning Tower of Pisa Scavenging Theory, for example; with the FOS images copy-pasted directly into the books chapters.

I have not heard Frits actual opinion on the matter, but quite a few commentors seemed to think it was less than ethical.

I actually dont know what the "story" is, so I am not making any direct claims, just sharing what I heard "on the internet" ;)

[Frits Overmars]

I once read that plagiarism is the ultimate form of flattery, but I'm not too happy about my views being contaminated with other opinions without it being clear that those are not mine.

[SwePatrick]

Hello guys!

I´ve been in a little bit of hiatus from this forum.
But work has still been done :Punk::Punk::Punk:

I´m working as we speak on two different projects, and has finallized a another one, Zundapp 20whp+ 66cc, went very good, like a lot of plus :gob::gob::gob:, reached physical limits, 24whp at ~13300rpm
But it took me one crankshaft and three pistons, and hundreds of dynopulls, hours and hours testing, videos are available at my youtube channel.

Today though my TZR250 get´s the most attention, in posted video below i´m talking about that dimpling that has been taken too far on the web ;)
Also i have taken the challenge to try to cast a new intake for my old vintage KTM 125cc RV engine, small glimpses of that, me trying to shape a wooden plug.
So, no 3d printing, i´ll do it the old way, wooden plug and sand cast.

Yesterdays video and some playlists below:
Small things takes forever to get done! :facepalm::blink::yes::yes:


https://youtu.be/fnq2gH-J_q0

Zundapp project:
https://www.youtube.com/watch?v=GakCxxwjyps&list=PLLDlMxsVSMz9OyCijmCQ7CWvUDKS-hkIB

Yamaha project:
https://www.youtube.com/watch?v=56nynYbnbOY&list=PLLDlMxsVSMz8EqAOqhlZlzqZzinLcBSzz

[Peter1962]

you could go even further : why not start with an Aprilia RSA125 ?
it doesn't matter what your starting point is, what matters is that what he is saying works. what matters is using cheap-ass engines available to everyone and one can do the same and check that the writers results are correct. when proven right, aply the same theories to whatever you want.

The KTM 250-300 range (latest evolution was 2025) and also the 125 (latest evolution whas 2023), and the yamaha yz 125 (latest evolution was 2023) and its much older brothter the yz 250 (basicaly still the same engine as the 1999 version...) are the bulk of the actual two stroke market anno 2026. Plus the boutique brands like TM, Sherco and Beta, primarily in the enduro market, not so in the MX market. They are produced in big numbers, don't you think thats a more realistic and relevant starting point then an obsolete soft-enduro bike from decades past ?

There is no problem with nostalgia. I like nostalgia myself.

But when it comes to evolution, I think it's more interesting to see the posibilities in reference to 2026 technique than to 1985 technique.

[Peter1962]

Here is the resident BRC Towel Head with his new RPG I did for the 500cc mini sprint dirt trackers.
I will let you know if the NSA is watching this.

:laugh::laugh::laugh:

Better than a Javelin !

Ideal to blow the competition away.

[Condyn]

I have a question regarding a figment of my memory that might not exist in reality lol. I seem to remember Wobbly saying the first signs of detonation are visible on the bottom of the piston ring. If this is in fact true, how and why is that the case? And if I am way off, sorry In advance.

[pete376403]

I have a question regarding a figment of my memory that might not exist in reality lol. I seem to remember Wobbly saying the first signs of detonation are visible on the bottom of the piston ring. If this is in fact true, how and why is that the case? And if I am way off, sorry In advance.

Jennings said the char on the underside of the piston crown was his best way of determining jetting and (possibly) onset of detonation. I recall he wrote the underside could be "black as an AMA race officials heart" and be ok but once it started to char, disaster was close by.

[wobbly]

Condyn, it may be a figment, but not of your imagination.
The greatest heat path from the exposed piston crown , is thru the ring, out to the bore.
Under compression pressure the ring is forced out, and downward onto the pistons bottom groove face.
When excess pressure and or temperature reach a critical level, this initiates the formation of free radicals , by spontaneous disassociation of the fuel/air mixtures chemical structure.

The creation of free radicals has two end results.
The formation of shock waves thru the combustion space ( knock ), and secondly, the huge amount of energy required to start this process is removed from the fuels available finite energy value.

This unauthorized use of the available fuel energy dramatically reduces the combustion temperature, and thus EGT drops.
Free radicals are highly reactive, and as the hottest place to see their formation ( the ring's bottom seal face ) this is the area that is the first to be attacked by the free electrons trying to return to their correct valency.

Thus one can detect the free radical formation at its earliest stage, as pitting on the on the ring bottom surface.
The next area to be attacked by the rampant recombinant seeking electrons, is the overheated sharp piston timing edge and the squish bands extremities.
This pitting is the very earliest sign of detonation, and was considered as being the absolute limit of tuning, without a power reduction.
It was coined by my ex boss - Franco Drudi of TM fame , as " power detonation ".

But as even forming a few random free radicals, must by definition , be removing combustion energy, this empirical postulation is flawed.
Thus I abandoned the idea, and started to closely monitor EGT delta's as the carb was leaned down.
This ended up as my assertion that by taking the " best power EGT " number from the dyno ( the EGT number where one jet size did not increase the temp by the same set amount as previously )
and plotting that against the Density Altitude, you could create a highly accurate spread sheet graphical guide for jetting on any day.

Here is my document showing this with a sample graph.

Forza Bez

[Condyn]

Thank you for the explanation. It matches what I am seeing. My customer sent me his datalog Which seemed strange to me because there was random downward spikes in the rpm logs which mostly occurred late in the races, or at the end of a long straightaway. His wash was non existent but the transfer windows/ducts looked somewhat wet. The plugs look like they have flecks of aluminum on them, but it must be microscopic damage because the pistons look undamaged, unless the flecks are coming from the ring grove ( which I have not asked for a photo of ) where it is getting pounded by the ring. 357855357856

[wobbly]

A normal ring has a bright shiny bottom surface from being pressed down and moved back and forth into the Exhaust port.
That ring has serious deto, the bottom ring groove face will be torn up.
The EGT dropping at the end of the straights is a sure and obvious sign deto is occurring.
Kart datalog gauges have warning lights to show just under the max achievable EGT value and prevent damage.

[porttiming124]

Question for Wayne. You already said that on a 2-cylinder engine with a Y-pipe, you cut the piston skirt on the exhaust side so that the exhaust port remains slightly open when the piston is at top dead center. Is this a fragile area? If I run tests on the dyno, can I go to 1mm per step? How many millimeters did you leave the port open when you were finished? Do you remember, to give me an idea please?
Thank you .

[wobbly]

The initial engine was a " stock " SeaDoo 951, this had the skirt 3mm above the port floor.
This created havoc with the tuning of the pumpers, that were already severely reverse jetted at about 2 1/2 B - 1/4 T.
That wasnt possible with the cut skirts, and the needles ended up near closer together.
It was near on 4 boat lengths faster to the first buoy, and won a title at Havasu.

Another cheat on that engine was a clear ceramic coating on the piston crown and combustion chamber, inboard of the squish area.
The tech officer commented that it was no wonder we had won so easily, as the squish was shinny metal, and inside that was real burnt black - and no one else had that clearly defined pattern.
I said " yea I tuned it near death ", which was close to the truth.

Later we did a stroked/big bore open class SeaDoo at 1140cc with twin pipes and fuel injection - the cut skirts did not work in that scenario.

[lodgernz]

A normal ring has a bright shiny bottom surface from being pressed down and moved back and forth

That's what Epstein said

[wobbly]

That's what Epstein said.

Reminds me of a visit to the doctor where I told him my anus was painful - he said where exactly, my reply was around the entrance.
He said as long as you keep calling it an entrance , it will keep on being painful.

[lodgernz]

.

Reminds me of a visit to the doctor where I told him my anus was painful - he said where exactly, my reply was around the entrance.
He said as long as you keep calling it an entrance , it will keep on being painful.

Almost wet myself larfing!

[wobbly]

For more information there is this unwanted but apparently thoughtful Xmas gift. Free to anyone wanting to bone up on the subject. Very in depth.

[porttiming124]

The initial engine was a " stock " SeaDoo 951, this had the skirt 3mm above the port floor.
This created havoc with the tuning of the pumpers, that were already severely reverse jetted at about 2 1/2 B - 1/4 T.
That wasnt possible with the cut skirts, and the needles ended up near closer together.
It was near on 4 boat lengths faster to the first buoy, and won a title at Havasu.

Another cheat on that engine was a clear ceramic coating on the piston crown and combustion chamber, inboard of the squish area.
The tech officer commented that it was no wonder we had won so easily, as the squish was shinny metal, and inside that was real burnt black - and no one else had that clearly defined pattern.
I said " yea I tuned it near death ", which was close to the truth.

Later we did a stroked/big bore open class SeaDoo at 1140cc with twin pipes and fuel injection - the cut skirts did not work in that scenario.


It couldn't be clearer, thank you Wayne.

[koenich]

Several racebikes I look after already have the Mychron 5 2T with expansion to run 2X EGT - so I am looking for the most cost effective way of getting suspension data into
that package.
Bit older but might be still of interest - just saw that you can expand the Mychron 5 and 6 with an ACC3 - Analog Can Converter which runs @ 1000 Hz, not limited by the 25 Hz of the Mychron.

https://www.aim-sportline.com/en/products/acc3/documentation.htm#start

Can purchased for all sorts of inputs, e.g. 2 x TC and 2 x Analog 5V for suspension or 4 x Analog 5V.

[Flettner]

In reality, how useful would Engmod2 be for optimizing my AG100, twin port?
Or my new disc valve engine with the VVT sliding gib. Also twin port.

[Vannik]

In reality, how useful would Engmod2 be for optimizing my AG100, twin port?
Or my new disc valve engine with the VVT sliding gib. Also twin port.

As soon as you have activated your copy I will send you a pack file of the Greeves Oulton with two exhaust ports and exhaust pipes. So no problem with the first part. I am working on the second and third parts - variable disk valve timing and inlets on both sides. It can already do a 3 cylinder Volvo Penta (designed by Konig) that has two rotary inlets on the center cylinder.