ESE's works engine tuner

[aljaxon]

You are trying to mix the FOS concept with the Wobbly concept and you were told more than once that it won't work. I've been trying to answer your questions in the French Pit-Lane forum, but as several people pointed out, you keep repeating the same questions when the answers do not suit you. You even started a new Pit-Lane thread to do it, and now you come here to do it once again.

You'd be wasting valuable time doing that. A typical suction wave might travel at about 300 m/s while a typical stuffing wave might travel at about 600 m/s.
Suction waves always travel slower than stuffing waves. Some reading about gas dynamics might be useful.
Re your quest for a wider power band: forget about cone angles for a while. Concentrate on Helmholtz resonance and try a shallow header in combination with a large pipe volume.


i'm sure ive read about Helmholtz briefly maybe even on this thread or the pit lane. i will read up again.

before the waves return back to the cylinder i assume they all travel at the same speed outwards. so its only on the way back where the speed differs?

i wanted to design a pipe working out the differing gas speeds and the differing speeds of the crank to see if i can get some magical design. but if its a waste of time then i have to copy others.

[aljaxon]

snip . Concentrate on Helmholtz resonance and try a shallow header in combination with a large pipe volume.


ive had a good search and a read including your post on pitlane and im trying to figure out how the resonance affects an exhaust pipe. thinking this had to be 90 degrees like blowing over the bottle. resonator. then i wondered a helmoltz resonator - is that much like a boost bottle?

then i wondered has anyone designed a helmholtz resonator for the exhaust pipe attached at the header to change the wave speed to a particual speed to suit the pipes dimensions? im assuming the resonator overides the initial speed of the wave and its its volume that dictates the outgoing speed?
if so, you could have a motor controlled piston to reduce or enlarge the size of the resonator to govern what speed you want the waves at. in effect peak power at all the rev range. including tickover.:eek:

if only things like this worked in real life.

[Frits Overmars]

.. im trying to find a pipe to work with the wobbly duct. you told me the FOS concept wont work with it. but you say the FOS concept is a good start point from which to test and develop, can i not do the same so as to get it working with the wobbly duct? Read my lips: no. And I repeatedly told you why: the FOS concept is based on the exhaust port blowdown area. The Wobbly-duct is based on the total exhaust port area.
i still want to know what i CAN do in the way of designing a pipe to go with the wobbly duct. can you or anyone please explain in simple terms why the FOS wont work with the duct? I just did. I cannot think of any simpler terms.
is the thinking that smaller belly diameter is for wider power motocross and larger belly diameter is for gp race bikes held by both jennings and blair not valid anymore? and those constants 2.125 - 3.5 x ex port diameter for the mid section are not applicable?You're doing it again: I tried to give you a guideline earlier today and you keep questioning my advice. Then what is the point of asking for it?
...has anyone designed a helmholtz resonator for the exhaust pipe attached at the header to change the wave speed to a particual speed to suit the pipes dimensions? im assuming the resonator overides the initial speed of the wave and its its volume that dictates the outgoing speed?Honda, Suzuki, Kawasaki and a dozen other manufacturers did. And no, a Helmholtz resonator does not alter the speed of the wave; it alters the frequency of the system.
You may want to take a look at https://1drv.ms/u/s!Atyzb5b7jtWNmVcX3c8D4Xr5eKjL?e=nxuw41 ; look for 'Helmholtz Blues' in the folder 'FOS tips & concepts'.

[wobbly]

Frits is correct , his calculations for pipe dimensions are based on the Exhaust Blowdown value - and this is of course directly related to the bmep capability of the engine.
All my rule of thumb does is give a guide as to what the exit area of the duct should be , but , again this is not bmep dependent.
It should be based on Blowdown , but , all I have done is looked at literally hundreds of worked projects and extrapolated the data that works as a baseline based on the Exhaust port effective area.
Historically we have been advised to make the duct exit anywhere from 100% to 120% , and that simply does not work in engines that are modified to achieve anything like decent power outputs , more
especially when Blowdown ( not even mentioned as a factor in Jennings book for example ) has been optimized to the bmep projection.
To convert the rule of thumb to be based on Blowdown isnt going to happen , to me its like obsessing over variable wave speed when you dont have a grasp of even basic pipe geometry.

[aljaxon]

You are trying to mix the FOS concept with the Wobbly concept and you were told more than once that it won't work.

frits this is off the janbros excell and this is where i first heard of the wobbly duct. maybe it needs editting?

In the original FOS PIPE, you have the possibility to integrate a Wobbly Exhaust Duct/Spigot.
This greatly improves performance. Chose 1 at number of exhaust ports if you have a single exhaust port, chose 2 when you have auxiliary
ports or a double port. Single port needs 90% cross sectional area and multiple 75%, at 1,5 times bore distance, see picture.
Untill that point, you do not "round of" the duct much, the transition to fully round is done in the spigot (from 1,5 to 2* bore), with and end-diameter-area that eaquals
the total exhaust port area.

[aljaxon]

Frits is correct , his calculations for pipe dimensions are based on the Exhaust Blowdown value - and this is of course directly related to the bmep capability of the engine.
All my rule of thumb does is give a guide as to what the exit area of the duct should be , but , again this is not bmep dependent.
It should be based on Blowdown , but , all I have done is looked at literally hundreds of worked projects and extrapolated the data that works as a baseline based on the Exhaust port effective area.
Historically we have been advised to make the duct exit anywhere from 100% to 120% , and that simply does not work in
To convert the rule of thumb to be based on Blowdown isnt going to happen , to me its like obsessing over variable wave speed when you dont have a grasp of even basic pipe geometry.

well im confused so much now. ive made pipes using blair and FOS but just blagged the starting diameter to match my cylinder. and the pipes have worked well. not brilliant. and not much difference between them

i will use those generally accepted angles for my header diffuser and rear cone that you brushed upon and have mentioned previously and also stick to those percentages.
i think i do have a grasp of basic pipe geometry but most of it is from jennings and blair. sharp angles = peakier but narrow power. and the opposite.

i am feeling like ive asked for too much info, testing the patience of people much in the way of asking lionel messi how to tie his shoelaces. maybe im trying to check formula 1 trye pressure by kicking them

so ill just be a silent observer from now on.
thanks for the suggestions.

[aljaxon]

Read my lips: no. And I repeatedly told you why: the FOS concept is based on the exhaust port blowdown area. The Wobbly-duct is based on the total exhaust port area.I just did. I cannot think of any simpler terms.You're doing it again: I tried to give you a guideline earlier today and you keep questioning my advice. Then what is the point of asking for it?Honda, Suzuki, Kawasaki and a dozen other manufacturers did. And no, a Helmholtz resonator does not alter the speed of the wave; it alters the frequency of the system.
You may want to take a look at https://1drv.ms/u/s!Atyzb5b7jtWNmVcX3c8D4Xr5eKjL?e=nxuw41 ; look for 'Helmholtz Blues' in the folder 'FOS tips & concepts'.


frits thanks for taking the time to give me advice but im not clever enough to take a lot of it on board. and you have run out of patience with me a long time ago and im not learning anything.
i wont bother you again.
but i will add this
what ive found with your FOS is that to derive at D1 you calculate lmax and X but the figure doesnt always match up with what the cylinders actual diameter is. and there is no deviation on that.
sometimes the cylinder cannot be altered if you wanted to keep the period header attachment circular nut.
all i ever wanted was a way around that discrepancy in diameters
but i never got one from you.
cheers
ill let someone else bug you.

[JanBros]

frits this is off the janbros excell and this is where i first heard of the wobbly duct. maybe it needs editting?

In the original FOS PIPE, you have the possibility to integrate a Wobbly Exhaust Duct/Spigot.
This greatly improves performance. Chose 1 at number of exhaust ports if you have a single exhaust port, chose 2 when you have auxiliary
ports or a double port. Single port needs 90% cross sectional area and multiple 75%, at 1,5 times bore distance, see picture.
Untill that point, you do not "round of" the duct much, the transition to fully round is done in the spigot (from 1,5 to 2* bore), with and end-diameter-area that eaquals
the total exhaust port area.

I already told you I'm about as novice as you (well, not quite as novice as you I know now, but certainly no expert), and my excell isn't the truth, the whole truth and nothing but the truth
it simply gathers all the info the true experts have given (for free, tnx again :not:, also the reason I put it on the internet for free, I wouldn't dare to ask money for idea's and concepts that are not mine) . if you have read the doc I also put online, you would already know this, and the "FOS concept" is included in it, in which you can see the Wobbly duct isn't part of it. And it is not because I integrated it as an option or say/quote some things about it, that it automaticaly means everything I say in it is 100% true or compatible.
It helps me and hopefully others to have fun while playing with and trying to improve 2-stroke engines. no more, no less.

[Frits Overmars]

frits this is off the janbros excell and this is where i first heard of the wobbly duct. maybe it needs editting?

In the original FOS PIPE, you have the possibility to integrate a Wobbly Exhaust Duct/Spigot.....Yeah, that text might steer you in the wrong direction, Al. I had nothing to do with it and for all I know neither has Wobbly.

[JanBros]

what ive found with your FOS is that to derive at D1 you calculate lmax and X but the figure doesnt always match up with what the cylinders actual diameter is. and there is no deviation on that.
sometimes the cylinder cannot be altered if you wanted to keep the period header attachment circular nut.
all i ever wanted was a way around that discrepancy in diameters


that is not the fault of the FOS concept, but the "fault" of the cyllinder-maker. it is up to you to be creative and adapt.

[wobbly]

So this is where we get differing perceptions on what is possible.
In the current fastest 125 engines on the planet I get the roof of the duct TIG welded and then its re machined on a 6 axis Rottler CNC designed for cutting 4T head ports.
Costs an absolute fortune to gain about 1 Hp in 50.
And in so many projects I simply couldn't count , I have counterbored the Exhaust duct then pressed in and welded an insert to be able to reduce the exit diameter.
Both are " easy " if you are trying to achieve the best result.

[F5 Dave]

If it had pedals, we didn't get it. No need for our rules.

(OK a friend has a solex somewhere). But all the 50s we git worth mentioning were the std non pedal, non restricted versions. At least my frame of reference the 80s.

We got A50, RD50, MB or MT50, GT50. Then RG50. Then a few exotics like RZ50, TZR50, Derbi,
Aprilia. But those weren't official imports.
I think it was the mid 90s before you couldn't put your learner arse on an RGV250 so pedallies weren't a thing.

Maybe you could ride a scooter on a car licence. Too far back.

[TZ350]

.
353963

Is there no winning with this thing!!!! Now that I have found a way to stop it shaking its cylinder hold down nuts loose. It has started cracking its cylinder. Crack runs between two cylinder studs and right through the transfer duct.

[Grumph]

As long as it's not an air leak - and the liner is still intact and in place - keep going.
There's a process used to make porous castings good which involves using epoxy under vacuum.
Wouldn't surprise me if someone in Auckland can do it if it becomes necessary. Neil would know.

BTW : What was the solution with the nuts ?

[TZ350]

As long as it's not an air leak - and the liner is still intact and in place - keep going. There's a process used to make porous castings good which involves using epoxy under vacuum. Wouldn't surprise me if someone in Auckland can do it if it becomes necessary. Neil would know.BTW : What was the solution with the nuts ?

Thanks for the epoxy idea. I had not thought of that but I have some experience with vacuum impregnating magnet coils, so might be worth a try. But there are holes and the transfer port edge has distorted. I might get it welded and then finish it off by vacuum epoxying it.

Nordlock washers were the solution.

[aljaxon]

So this is where we get differing perceptions on what is possible.
In the current fastest 125 engines on the planet I get the roof of the duct TIG welded and then its re machined on a 6 axis Rottler CNC designed for cutting 4T head ports.
Costs an absolute fortune to gain about 1 Hp in 50.
And in so many projects I simply couldn't count , I have counterbored the Exhaust duct then pressed in and welded an insert to be able to reduce the exit diameter.
Both are " easy " if you are trying to achieve the best result.


wobbly on that 50v i did not want to alter the cylinder. i wanted it to look standard.

but on this latest puch project i have indeed welded up the duct and machined it so the diameter matches perfectly with your ducts converging 1.5 x bore bit. i even got a cone section at the correct diameter and flatten it slightly oval so as to machine the cylinder outlet to have the same ovality. and then the rest or the 1.5 duct goes back to circular.


i considered doing what you did - counter boring and fitting an insert but there would have been a step somewhere or gaps at the sides where the port diverges more than the insert that would have needed welding (cant do ac welding)

unless i really go overboard on the insert outside diameter.... penny just dropped.

btw this is me being silent.

[aljaxon]

Yeah, that text might steer you in the wrong direction, Al. I had nothing to do with it and for all I know neither has Wobbly.


frits i think you need to grasp that sometimes it appears i am not listening. i am listening, but sometimes i dont understand.
and so if i focus on things i do understand and conveniently ignore those i dont it makes me look like i am reading what i want to read.

its not through ignorance, (well it is in some meanings of the word as in not aware). i am not ignoring you but some stuff just stalls in my brain.
i am struggling to take a lot of this on board

i cannot understand the difference between a pipe designed for blowdown area and one for the ports actual area and if my blowdown are is effective diameter 18mm as opposed to actual 25mm how i use the 18mm in pipe design.

so much for me staying silent.

[aljaxon]

If it had pedals, we didn't get it. No need for our rules.

(OK a friend has a solex somewhere). But all the 50s we git worth mentioning were the std non pedal, non restricted versions. At least my frame of reference the 80s.

We got A50, RD50, MB or MT50, GT50. Then RG50. Then a few exotics like RZ50, TZR50, Derbi,
Aprilia. But those weren't official imports.
I think it was the mid 90s before you couldn't put your learner arse on an RGV250 so pedallies weren't a thing.

Maybe you could ride a scooter on a car licence. Too far back.


sounds a lott better than uk

my time was the 70's -50 cc with pedals (no honda c50) until 17, then a 250 on L plates then pass your test (10 minute piece or proverbial) and then ride anything. it changed around 1978 with mopeds restricted to 35mph and 125 the limit until you passed your test. and there was a time limit so this now expensive test £500? sent a lot of prospective bikers off the road to buy cars.

[Frits Overmars]

what ive found with your FOS is that to derive at D1 you calculate Lmax and X but the figure doesnt always match up with what the cylinders actual diameter is. and there is no deviation on that.
sometimes the cylinder cannot be altered if you wanted to keep the period header attachment circular nut.
all i ever wanted was a way around that discrepancy in diameters but i never got one from you.Al, it would be a shame if our paths parted in this way. But the aspect in which the FOS exhaust concept distinguishes itself most from other concepts is the determination of the initial diameters. And if those are too large in an existing cylinder, you have just two options: throw it away or apply an insert, like Wobbly just wrote. In almost all cylinders you can do that without changing their outer appearance.

Looking back at my contributions I found this picture of a KTM 50SX cylinder with a clearly oversized standard diameter, and of the same cylinder with an insert.
This picture is over ten years old and I posted it in KiwiBiker, Pit-Lane, Facebook and four other forums, so there has been ample opportunity to find it.
I know it's nearly impossible to check everywhere, but you must realize that it's totally impossible for me to tell every questioner where to find the answer to every question.
That is your own responsibility.
​Keep asking questions, but also do your own research so you won't have to repeat every mistake I and others have made in the past.
353967 353966

[aljaxon]

thanks for that frits, of course you are inundated with questions from all angles and thats one of the reasons i repeated the same question thinking you may not have seen it. you should have told me to go and play with diesels engines instead....

ive read everything in your files. even tried one of the dutch ones using google translate.

i am going to splash out on an ac welder (only got dc atm) so i am not hindered anymore by big holes.

[Condyn]

You can weld aluminum using a dc tig with the flux coated aluminum sticks.

There is no magical calculator or formula for making the best pipe possible in the field. You have to test dozens of designs. The dyno/sim only does part of the work. I have pipes that dyno like shit, but hoard trophies on race day via the dynamics posed by the specific application. Start rolling cones

[palezu]

Hello fellow 2-stroke sufferers,
I want to do a report of my High Power 50cc project after some 2 years of trials and tribulations.
In 2021 I cast this 50cc watercooled cylinder from cast iron (the sewing machine, some may remember).
It was supposed to be a record breaker. I based the radial transfer angles on Frits' MB40 transfer angle picture: https://servimg.com/view/19023519/1#
The axial angles were 20*(A), 10*(B) and 55 for C. (Now that I look at this again, I realize that the axial angles in Frits' concept are much different...doh.)
The inner wall is a "generous" bulge without much thought put into it. The transfer entries are also not much thought, I just drew something that roughly resembled Frits' MB40 cylinder.
The cylinder is mounted to AM6 engine using a 15mm thick spacer plate which is probably very unideal. The transfer ducts are very short.

The exhaust duct is a normal 3-part, with wobbly's 1.5*bore length and restricted outlet area. The duct is water cooled on the top side completely. The auxiliary ducts are very long and quite slim, later I shortened the bridges quite a lot.
Main exhaust port floor is 3mm above BDC.
I made a lot of errors with the exhaust port design. At first I made it too low and the timing was only about 185 degrees. This was because I had thought that a properly designed auxiliary duct would flow so well that
the cylinder would easily surpass a typical power of a stud-compromised triple exhaust even with a low timing.
I made the auxiliary windows quite small, there was a lot of room to enlarge them. Then I made the outlet about 75% of the port effective area, but since the cylinder ports were already small, the outlet area ended up being equivalent to only a 20mm round port which was way too small.

On the first tests the cylinder was about as weak as a unported stock AM6 cylinder with a general powerpipe. My pipe is made with Blair's formulas, designed power peak at 14000, belly diameter 82mm, tuned length 710mm. At first only about 8hp at the rear wheel and not much revs.

First major improvement came from raising the exhaust port to 198 degrees and enlarging the auxiliaries. Peak power didn't improve much but I got way more usable range on high rpm. Second major improvement was again from the exhaust area, by enlarging the duct and header diameter from 22mm to 25mm brought some 2.5hp more power. Record power is now 12.5hp at 12800 measured on rear wheel. With some fine adjustment and a new piston ring I think it could do close to 13. But still that is nothing. This cylinder design is ought to give 18+ rear wheel horses when you think of all the ideas that have been read from this forum and implemented.

In addition to those mods I have also tried almost everything else possible. I have tried compression ratios of 15:1 and 13.5:1 with maybe only a slight improvement on rpm range and less power. I have tried 53% and 40% squish ratio, squish gap from 0.4 to 0.65mm and different ignition timing without much improvement to speak of.
Porting the cases for a more direct reed flow path. Different reed valve. Much stiffer petals. Different manufacturer carburetor. Basically only loses power or there is only a very slight improvement. My last trial was the crankcase compression. Changed the compression from 1.19 to 1.23 with a 45cc stuffer. The crankcase volume at TDC is 266cc by the way. Crankcase compression did nothing, only lost power on powerband beginning.

Current tail restriction is 15mm. I also tried to make a completely different looking exhaust with a 20mm fatter belly and about 30mm shorter TL. Even this was a failure, there was noticeably less peak power but the rpm range was pretty much identical.

I still have some hope of getting a bit more by enlarging the exhaust duct further. Apparently the 75% rule doesn't seem to work in a 50cc cylinder. At least I can assure it doesn't work if the cylinder ports are even a little bit on the small side.

But I would be surprised if enlarging the duct a bit more would give more than 1hp. It may be the case that the FOS-MB40 transfer concept does not work in a 50cc cylinder, or then I have done something wrong. Many people think that it is the missing B duct hooks that cause it but I really doubt that. 2strokestuffing had already tried to add the hooks and it didn't seem to do much at all. (but he too had a badly restricted exhaust channel which probably hinders all other changes). I have also tried to choke the B ducts with 3D printed plugs but didn't get a breakthrough. Funnily enough, adding a plug which reduced the entry area to maybe 15% of the original, in only the LEFT B duct, didn't make any difference to the power curve. Adding plugs to both ducts reduced power a lot.

Description for pictures:

1. cores in the mould. The water flow is so that cold water enters the cylinder head from the C port side and flows out above the exhaust duct. The engine stays remarkably cool under driving conditions with a standard Derbi moped radiator, which I think may be an indication of the effectiveness of the "reversed" water flow heat transfer. Or then it is just due to low power.
2. transfer duct top view
3. B duct side profile. The duct is modeled in the cad as if the cylinder bore was 36mm for core making reasons. The 2mm straight part is bored out.
4. Cylinder with some machining done
5. Cylinder adapter plate in the cases. There is also a resin-silicone-mess crankcase stuffer there which failed miserably later.
6. Exhaust port after raising it to 198(main port, aux is a bit lower)

One friend has an AM6 engine with an original single exhaust port Minarelli cylinder, another guy ported that cylinder and the bike pushed out 12.4hp to the rear wheel, so my cylinder is clearly failed. I am desperate to get more power next year but haven't yet made up my mind what to do next :rolleyes:. Maybe a new cylinder but what to change?

[wobbly]

Here is a few ideas for you.
Years ago I did an RG50 Gamma based engine in EngMod shooting for 20Hp @ 13500 on AvGas.
The TL was 738 with an 80% duct exit of 23mm as this wasnt changed from stock, the stinger nozzle was 13.7mm and the mid was 106mm.
Porting was simply a scaled down RS125 Honda as it had a T port and the axial angles turned out to be exactly as Frits later produced drawing suggested.

Case compression was 1.3 , as anything bigger than this with reeds is doomed to failure , only a Rotary Valve engine would be happy at a big 1.23 ratio.
Big cases over 1.3 ratio need very thin reeds to match the Helmholtz forcing frequency mid powerband , and of course they then flutter like hell and destroy themselves in protest.
It had a VF3 from a KX85 in it - too big really but it was the best I could find at the time and it fitted easily enough with some welding on the case and cylinder.

This engine made 17.6 Hp @ 13600 sprocket power - so all but exactly the simulation crank power that was predicted.
It could have made more at higher rpm but using the stock gearbox the rev drops were to large to expect a bigger bmep to work effectively.
Bottom line is that if everything is matched correctly in EngMod the result is as expected , every time.

EDIT - having the Exhaust duct 3mm above BDC has been dyno tested and proven to work in full noise 125 engines - no one to my knowledge has been any higher and proven the concept on a dyno.

[palezu]

Regarding the case compression. I am thinking that I should have seen an improvement by changing it into the right direction but there was a major loss about 1000rpm before peak power. The 45cc (47.6cc) stuffer reduced the TDC volume by 15%. Feels like the change should be apparent.
Or maybe the choice of reeds is now wrong. Before the case stuffing I had softer reeds(didn't measure) and then changed to 0.4mm (and lost a lot of midrange but gained a little top). After case stuffing I still have the thick reeds. Maybe the softer reeds would work better now. It is tiring, seems there is always a possibility that one change is ruined by another...

[wobbly]

Well its the old story of bullshit in = bullshit out. When you are miles away from optimum and take a step in the right direction there are no rules that
say that improvement will do anything to help.
When you have a whole string of sub optimum choices the chances of getter anything meaningful with a single change are close to zero.
I have 10 disappointments on the dyno most days , if one tiny thing works without needing 3 other changes to regain synergy I'm over the moon with joy.

[Jan Van Hamme]

Hi,
Can anyone give advice please? If you need to shorten a piston skirt, how do you rebalance the piston?
With the method in the left column or the right column?
Best regards Jan.

353983

[Ns1Montesa]

Hi,
Can anyone give advice please? If you need to shorten a piston skirt, how do you rebalance the piston?
With the method in the left column or the right column?
Best regards Jan.

353983

Hello Jan. I would say balancing it like on the right side of your drawing makes more sense. Imbalance between right and left side of the wrist pin leads to a torque around the wristpin when Piston is accelerated. Would be interessting how high the resulting forces are.

[aljaxon]

You can weld aluminum using a dc tig with the flux coated aluminum sticks.

There is no magical calculator or formula for making the best pipe possible in the field. You have to test dozens of designs. The dyno/sim only does part of the work. I have pipes that dyno like shit, but hoard trophies on race day via the dynamics posed by the specific application. Start rolling cones

i missed this post. i did search to see if you can weld aluminium with dc and a youtube video showed a guy doing it. he reversed the polarity and the welds looked terrible but held fast. i tried it with a flux coated stick scrounged of a welder pal last year. he told me to scrape the flux off? i may have tried both ways i cant remember it was last year on a stud hole i'd gone through via the ex port. all i got was just a sparkly fizzing mess. some guy said you need helium?

ive only wanted an ac rig for almost the last 10 years and its nearly xmas....

as for pipes i know without a sim and just a dyno im not going to be able to test and refine and then repeat this noting improvements.
peeing into the wind trying to find the best pipe.

i will make two pipes for this project same percentages length wise but slightly different angles and just select the best performance.
it will be pot luck narrowed down by using recommendations on here etc.

i made 2 sets of pipes for my rd350 and settled with the second set and that was 12 years ago. im know they could easily be bettered but they seem good enough.

this was the constrictor on my mobylette that i didnt want to change. i did bore it out so it was wafer thin. and on another cylinder i binned that mounting idea and used studs.

https://i.ebayimg.com/images/g/48IAAOSwbkdhxHDg/s-l1600.jpg

[aljaxon]

. It is tiring, seems there is always a possibility that one change is ruined by another...

lol isnt that the case. just with tweaking an exhaust design never mind all the variables you have to contend with.

[aljaxon]

. Concentrate on Helmholtz resonance and try a shallow header in combination with a large pipe volume.

hi frits, just read your helmholtz lesson translation and i think im 11yrs old.
im struggling to understand how when the pressures in Pcyl and Pout (pipe) are equal, that gives you maximum speed of the mass. isnt it already slowing down at this point?

all ive ever read about with pipe design is to do with the sonic waves and very little to the actual gas flow which i found weird because at first glance to the uneducated you would think an exhaust was only about gas flow. that is until you learn about the sound waves helping hands.

[beta]

Hello fellow 2-stroke sufferers,
I want to do a report of my High Power 50cc project after some 2 years of trials and tribulations.
In 2021 I cast this 50cc watercooled cylinder from cast iron (the sewing machine, some may remember).
It was supposed to be a record breaker. I based the radial transfer angles on Frits' MB40 transfer angle picture: https://servimg.com/view/19023519/1#
The axial angles were 20*(A), 10*(B) and 55 for C. (Now that I look at this again, I realize that the axial angles in Frits' concept are much different...doh.)
The inner wall is a "generous" bulge without much thought put into it. The transfer entries are also not much thought, I just drew something that roughly resembled Frits' MB40 cylinder.
The cylinder is mounted to AM6 engine using a 15mm thick spacer plate which is probably very unideal. The transfer ducts are very short.

The exhaust duct is a normal 3-part, with wobbly's 1.5*bore length and restricted outlet area. The duct is water cooled on the top side completely. The auxiliary ducts are very long and quite slim, later I shortened the bridges quite a lot.
Main exhaust port floor is 3mm above BDC.
I made a lot of errors with the exhaust port design. At first I made it too low and the timing was only about 185 degrees. This was because I had thought that a properly designed auxiliary duct would flow so well that
the cylinder would easily surpass a typical power of a stud-compromised triple exhaust even with a low timing.
I made the auxiliary windows quite small, there was a lot of room to enlarge them. Then I made the outlet about 75% of the port effective area, but since the cylinder ports were already small, the outlet area ended up being equivalent to only a 20mm round port which was way too small.

On the first tests the cylinder was about as weak as a unported stock AM6 cylinder with a general powerpipe. My pipe is made with Blair's formulas, designed power peak at 14000, belly diameter 82mm, tuned length 710mm. At first only about 8hp at the rear wheel and not much revs.

First major improvement came from raising the exhaust port to 198 degrees and enlarging the auxiliaries. Peak power didn't improve much but I got way more usable range on high rpm. Second major improvement was again from the exhaust area, by enlarging the duct and header diameter from 22mm to 25mm brought some 2.5hp more power. Record power is now 12.5hp at 12800 measured on rear wheel. With some fine adjustment and a new piston ring I think it could do close to 13. But still that is nothing. This cylinder design is ought to give 18+ rear wheel horses when you think of all the ideas that have been read from this forum and implemented.

In addition to those mods I have also tried almost everything else possible. I have tried compression ratios of 15:1 and 13.5:1 with maybe only a slight improvement on rpm range and less power. I have tried 53% and 40% squish ratio, squish gap from 0.4 to 0.65mm and different ignition timing without much improvement to speak of.
Porting the cases for a more direct reed flow path. Different reed valve. Much stiffer petals. Different manufacturer carburetor. Basically only loses power or there is only a very slight improvement. My last trial was the crankcase compression. Changed the compression from 1.19 to 1.23 with a 45cc stuffer. The crankcase volume at TDC is 266cc by the way. Crankcase compression did nothing, only lost power on powerband beginning.

Current tail restriction is 15mm. I also tried to make a completely different looking exhaust with a 20mm fatter belly and about 30mm shorter TL. Even this was a failure, there was noticeably less peak power but the rpm range was pretty much identical.

I still have some hope of getting a bit more by enlarging the exhaust duct further. Apparently the 75% rule doesn't seem to work in a 50cc cylinder. At least I can assure it doesn't work if the cylinder ports are even a little bit on the small side.

But I would be surprised if enlarging the duct a bit more would give more than 1hp. It may be the case that the FOS-MB40 transfer concept does not work in a 50cc cylinder, or then I have done something wrong. Many people think that it is the missing B duct hooks that cause it but I really doubt that. 2strokestuffing had already tried to add the hooks and it didn't seem to do much at all. (but he too had a badly restricted exhaust channel which probably hinders all other changes). I have also tried to choke the B ducts with 3D printed plugs but didn't get a breakthrough. Funnily enough, adding a plug which reduced the entry area to maybe 15% of the original, in only the LEFT B duct, didn't make any difference to the power curve. Adding plugs to both ducts reduced power a lot.

Description for pictures:

1. cores in the mould. The water flow is so that cold water enters the cylinder head from the C port side and flows out above the exhaust duct. The engine stays remarkably cool under driving conditions with a standard Derbi moped radiator, which I think may be an indication of the effectiveness of the "reversed" water flow heat transfer. Or then it is just due to low power.
2. transfer duct top view
3. B duct side profile. The duct is modeled in the cad as if the cylinder bore was 36mm for core making reasons. The 2mm straight part is bored out.
4. Cylinder with some machining done
5. Cylinder adapter plate in the cases. There is also a resin-silicone-mess crankcase stuffer there which failed miserably later.
6. Exhaust port after raising it to 198(main port, aux is a bit lower)

One friend has an AM6 engine with an original single exhaust port Minarelli cylinder, another guy ported that cylinder and the bike pushed out 12.4hp to the rear wheel, so my cylinder is clearly failed. I am desperate to get more power next year but haven't yet made up my mind what to do next :rolleyes:. Maybe a new cylinder but what to change?

If I could help you

1 the water jacket is too far from the transfers and in my opinion you need a lot more water around the exhaust duct, for me it stays cool because of the lack of power
2 transfers are totally wrong you need to measure the port area times the sin (axial angle) and then increase 7.5mm2 every 7.5mm of duct until the end of the duct, max area at the bottom need to be around 1.25-1.28 time the effective port area.
About port cordal lenght I think a good start is A port 0.426*bore, B port 0.41*bore C port 0.33*bore, Main Ex 0.71*bore and Aux 0.35*bore.
Position of the transfer ports really important: the divider from A to B (on the A side) move toward C port 0.12*bore.
Radial angles
A port: ex side towards the center of C, B side 15° towards opposite B (0° would be parallel to the piston pin)
B port : A side 10° towards C, C side towards the opposite exhaust divider
Axial angles
A port 25° min
B port 15° min
C port 55° min

3 totally wrong you have to adjust the shape and the area

on an am6 50cc I think 195-196 main and 191-192 aux would be good. the area of the aux duct at the dividers needs to be around 50% of the effective area of the aux port. 78-80% of the total area on the exit it's good
do a big staggered configuration on transfers like 132.5 128 126

If you make that corrections I think you can achieve 320-330cv/l (real)

PS
first you design the ports the rest of the duct geometry is a consequence

[Jan Van Hamme]

Hello Jan. I would say balancing it like on the right side of your drawing makes more sense. Imbalance between right and left side of the wrist pin leads to a torque around the wristpin when Piston is accelerated. Would be interessting how high the resulting forces are.

Thank you for explaining.
I have now calculated it at 11000rpm. I arrive at extra force of 9.275N perpendicular to the cylinder wall at the bottom of the skirt.

bore 57mm x stroke 50mm
Distance center wristpin to bottom skirt 33mm
Cutaway mass =4g
F=m.a
s=a.t2/2
v=a.t
M=F.s

That is 22000 times per minute 9.275N extra force on and off on the skirt at max rpm.

[Frits Overmars]

When you are miles away from optimum and take a step in the right direction there are no rules that say that improvement will do anything to help.
When you have a whole string of sub optimum choices the chances of getter anything meaningful with a single change are close to zero...........353985

[TZ350]

.

Hi, Can anyone give advice please? If you need to shorten a piston skirt, how do you rebalance the piston?

353986

Not sure if this is any help. Modified piston at the top. Suzuki RG50 Gamma 13 RWHP @ 14,000 rpm.
We cut the skirts on our Suzuki RG50's right back to get the inlet timing we wanted.
The exhaust side was left with enough to cover the exhaust port at BDC and the inlet side was cut back to the piston pin bosses.
Never had any problems with the pistons themselves.

[Ns1Montesa]

Thank you for explaining.
I have now calculated it at 11000rpm. I arrive at extra force of 9.275N perpendicular to the cylinder wall at the bottom of the skirt.

bore 57mm x stroke 50mm
Distance center wristpin to bottom skirt 33mm
Cutaway mass =4g
F=m.a
s=a.t2/2
v=a.t
M=F.s

That is 22000 times per minute 9.275N extra force on and off on the skirt at max rpm.



This were only my thougts about your problem. As I am only a amateur tuner i dont know if balancing piston plays any role at all. There are so many forces while a piston engine is rumning. I am not sure if 9N makes any difference.

Around two years ago I asked some questions in this thread about getting more power out of Honda MBX/MTXNS1 80cc engine.
When time allows I am still playing around. A few days ago I tried shorter intake. I followed Frits advice of making manifold as short as possible. Frits idea is to mount the carb via pinged O ring. I have to thank Frits for this idea.
Compared the shorty intake against an intake made of rubber, which is about 10mm longer. shorty gives more power across the whole power band. I am not smart enough to explain what exactly happens. But seems like reed Petals are open for longer time.
I think most people here already know about this effect. But maybe this is of interesst for some tuners. For this small amount of effort it is a good power gain. Around 0.4HP out of 20HP.

[wobbly]

To answer why intake length ( from bellmouth end + end correction to the reed tips ) is important and is capable of adding considerable Hp.
There are two pressure ratios that affect reed opening and the duration of the this lift period.
First is depression within the case , and second is the wave bouncing up and down the intake tuned length , off the atmospheric end.

The optimum length for a specific rpm is when the two effects are operating together , but of opposite sign.
That is , the case goes negative at the same time as the intake has a positive pressure ratio at the reeds - this opens them quickly and holds them open.
The effect has an effective range of around 2000 rpm and is most usefully tuned to be near peak torque.

Here is an example of where the intake needed lengthening by 20mm to get the red trace ( case pressure ratio ) crossing the zero line at the same time as the
intake yellow line crosses zero ( intake pressure ratio ).
Thus we get the most efficient sonic " supercharging " of intake flow into the case as shown by the reed tip lift rising dramatically as the two opposing pressure ratios act in concert.

The effectiveness of this is also shown in KZ engines , where with peak power around 13500 shortening the intake length by counterboring the reed flange face and inserting the carb
4mm closer is worth close to 1 Hp in 50.

[Jan Van Hamme]

.


353986

Not sure if this is any help. Modified piston at the top. Suzuki RG50 Gamma 13 RWHP @ 14,000 rpm.
We cut the skirts on our Suzuki RG50's right back to get the inlet timing we wanted.
The exhaust side was left with enough to cover the exhaust port at BDC and the inlet side was cut back to the piston pin bosses.
Never had any problems with the pistons themselves.

I read on forums when people adjust piston skirts (enlarge windows, extra ports, shorten) this often leads to breakage. The explanation on forums about this is that you weaken the piston and that you disrupt the balance of the piston.
That's why I asked myself "how do you rebalance a piston?".
To achieve the desired STA in Engmod2T I need an inlet area of 1277mm2.
The existing inlet in the cylinder must be enlarged. The inlet consists of 3 slotted holes. See picture.
There are 2 windows in the piston skirt and these are not the same shape as the cylinder inlet. There is obstruction of gas flow.
I would either make 3 appropriate holes in a new piston with a full skirt, or make a large cutout so that the cylinder inlet is free. But that quickly causes wear and rattling of the piston.
I would like to simulate this in Engmod2T, but there is no option to model 3 cylinder intake slots. There is also no option to model a piston with 3 slotted holes. A cutout can be modeled. Maybe it can’t be modeled because it is so unusual or because it is not right to do it that way?
Machining piston skirts in a cast piston leads to microcracks and ultimately to breakage. A forged piston can handle this better, I read on forums.
So to try to prevent breakage I would adapt a forged piston to cylinder inlet shape, balance it (but 9N extra force seems completely negligible to me) , make the cylinder inlet slots 1277mm2 and try it.

[F5 Dave]

My several iterations ago RG50 was reliable with full skirt (I got more than enough area by grinding std twin inlets downward) until the bore wore in that area. Then it would crack skirts.
The remedy (warning: Dad joke) was boring.

[Jan Van Hamme]

..........353985

Hello Frits,

I don't know if your quote was intended for me, but I do feel it applies to me.
I give my quote in a general form.

I understand English, French and a little German.
However, writing and speaking in those languages is a disaster. That's why I translate from Dutch to English. Sorry everyone for the grammar and language errors.
My native language is Dutch, I live in East Flanders, 100m from the Dutch border with Zeeland.

I am an amateur, a modest novice who realizes that he still has to learn everything that others have already forgotten.
There is the Master of 2stroke, Frits, Neels, Wobbly,... and others.
All people with an amount of knowledge and experience that could fill an entire galaxy.

I have deep respect for you and them.

I still have to learn how to roll a cigarette that looks like an expansion pipe. They and you have made countless of them.
I have not yet seen the needles of a needle bearing fly out through the carburetor. They do.
It almost makes me scared in these first posts to ask about something that could be ridiculous.

I read forums, Frits's columns and all his tips and tricks, I try to use/understand a little bit of Engmod2t, I read Jan's masterpiece book in one go.
There is so much info on forums that I have a hard time understanding some things.

2 examples:
Jan Thiel wrote that he has never understood why people try to make pistons lighter. With a heavier piston he could do many test runs without losing power, he said. I believe every word he says.
Frits advises and motivates to round off the piston edge instead of the transfers. Better piston head cooling and flow and behaves like a delaval nozzle on the exhaust side. I would therefore like to provide my piston with such a rounding. Do I also have to make the same rounding in the combustion chamber? If not, am I not creating a detonation in that "lost space" if this zone does not also have a rounding? Is this only recommended for racing? And do you just stay away from it for street use?

A combination lock of 10? I only have 1 of the 10 and I don't even know if it is correct. Let alone the other 9.
That's why I'm asking this novice questions.

Groeten Jan


regards Jan

[F5 Dave]

It amuses me that English as 2nd or 3rd language apologise for language, but invariably post more legibly than us native speakers.
Whatever you are using, continue with confidence,
Welcome.

[Vannik]

Jan Thiel wrote that he has never understood why people try to make pistons lighter. With a heavier piston he could do many test runs without losing power, he said. I believe every word he says.

My understanding of Jan's comment is based on the fact that Aprilia made pistons so light that after a couple of runs the dome started to sag and compression and power was lost. So it was not the mass of the piston Jan was addressing but its mechanical strength at in-cylinder temperatures and the fact they made them too light. If I misunderstood Jan please tell me.

[Frits Overmars]

Hello Frits, I don't know if your quote was intended for me, but I do feel it applies to me. I am an amateur, a modest novice who realizes that he still has to learn everything that others have already forgotten.
There is the Master of 2stroke, Frits, Neels, Wobbly,... and others. All people with an amount of knowledge and experience that could fill an entire galaxy. I have deep respect for you and them.
I still have to learn how to roll a cigarette that looks like an expansion pipe. They and you have made countless of them. It almost makes me scared in these first posts to ask about something that could be ridiculous.Hi Jan, don't you worry about ridiculous questions. Every day I encounter a level of ridiculousness that you couldn't equal if you tried. Yes, I am referring to Fakebook.
That 'combination lock' tile was intended to confirm a comment made by Wobbly, but I think it's applicable for all of us.
Rolling a cigarette that looks like an expansion pipe? I used to be proud of rolling them into a nice cylindrical shape while driving, with one hand, on my knee. But that was 50 years ago when everyone and their mother smoked. Speaking of smoking: when I was still commuting back and forth between the Netherlands and Italy, I always had to bring tobacco and sigarette paper for Jan Thiel because it was hard to find over there.
Jans philosophy about smoking: "I read that if you start smoking at the age of 17, your life expectancy is that you will live to be 57. I started smoking at the age of 37, so I will live to be 77 and I'll never make that without smoking!" (Jan hasn't smoked for years and he is now 83).

I read forums, Frits's columns and all his tips and tricks, I try to use/understand a little bit of Engmod2t, I read Jan's masterpiece book in one go. 2 examples:
Jan Thiel wrote that he has never understood why people try to make pistons lighter. With a heavier piston he could do many test runs without losing power, he said. I believe every word he says.
Frits advises and motivates to round off the piston edge instead of the transfers. Better piston head cooling and flow and behaves like a delaval nozzle on the exhaust side. I would therefore like to provide my piston with such a rounding. Do I also have to make the same rounding in the combustion chamber? If not, am I not creating a detonation in that "lost space" if this zone does not also have a rounding? Is this only recommended for racing? And do you just stay away from it for street use?If you radius the piston timing edge, you need to make the same radius at the outer diameter of the squish band in the head, otherwise you'd create a detopnation zone.
And it's generally applicable, not just for racing (I radiused the piston of my moped in 1963 because I had no way of raising the transfer ports without ruining their shape).


My understanding of Jan's comment is based on the fact that Aprilia made pistons so light that after a couple of runs the dome started to sag and compression and power was lost. So it was not the mass of the piston Jan was addressing but its mechanical strength at in-cylinder temperatures and the fact they made them too light. If I misunderstood Jan please tell me.Jan was well accustomed to sagging piston domes. The pistons in his 125cc Garelli engines self-adjusted to their working conditions that way and the engines ran fine with them, gaining six straight world titles. But the Aprilia was from a different level. The unbeatable Garelli 125 twins produced 46 HP; the Aprilia 125 single produced 54 HP, so the thermal load in the single was a lot higher.

​

[Jan Van Hamme]

Hi Jan, don't you worry about ridiculous questions. Every day I encounter a level of ridiculousness that you couldn't equal if you tried. Yes, I am referring to Fakebook.
That 'combination lock' tile was intended to confirm a comment made by Wobbly, but I think it's applicable for all of us.
Rolling a cigarette that looks like an expansion pipe? I used to be proud of rolling them into a nice cylindrical shape while driving, with one hand, on my knee. But that was 50 years ago when everyone and their mother smoked. Speaking of smoking: when I was still commuting back and forth between the Netherlands and Italy, I always had to bring tobacco and sigarette paper for Jan Thiel because it was hard to find over there.
Jans philosophy about smoking: "I read that if you start smoking at the age of 17, your life expectancy is that you will live to be 57. I started smoking at the age of 37, so I will live to be 77 and I'll never make that without smoking!" (Jan hasn't smoked for years and he is now 83).
If you radius the piston timing edge, you need to make the same radius at the outer diameter of the squish band in the head, otherwise you'd create a detopnation zone.
And it's generally applicable, not just for racing (I radiused the piston of my moped in 1963 because I had no way of raising the transfer ports without ruining their shape).

Jan was well accustomed to sagging piston domes. The pistons in his 125cc Garelli engines self-adjusted to their working conditions that way and the engines ran fine with them, gaining six straight world titles. But the Aprilia was from a different level. The unbeatable Garelli 125 twins produced 46 HP; the Aprilia 125 single produced 54 HP, so the thermal load in the single was a lot higher.

​

Thank you very much for the words of wisdom.
In 1963... I was -7 years old. (Born december 1970)

Without the radius of the piston timing edge I would normally have to make my transfer port 12mm high to get the desired timing (129.4°).
The radius increases the timing.
To achieve the same 129.4° I can only go 11.11mm high. This reduces the transfer window area.
Does this not have a negative effect on the power? Or does the flow improvement due to the radius fully compensate for this transfer area reduction?

[Frits Overmars]

Without the radius of the piston timing edge I would normally have to make my transfer port 12mm high to get the desired timing (129.4°). The radius increases the timing. To achieve the same 129.4° I can only go 11.11mm high. This reduces the transfer window area.
Does this not have a negative effect on the power? Or does the flow improvement due to the radius fully compensate for this transfer area reduction?A radiused piston timing edge, and a radiused top edge on the exhaust port, give a more gradual initial port opening. If we want the effective timing to remain the same, we can make the geometrical timing (when you see the first glimpse of light through the port) a few degrees higher. The mathematical difference is not so easy to explain but the best practical approach is to measure the port timings with a 0,7 mm feeler gauge bent at 45° and assume that radiused and non-radiused piston and port edges should give the same piston position when measuring.

[wobbly]

If you draw the radius piston concept out in CAD you will see that using the dead stop method ( standardized now as a 0.7mm blade that gives an easy calculation of 1mm of port height difference )
the cylinder will need to be dropped 0.6X the radius on the piston to get the same port height/timing.
Thus for a 1mm radius the cylinder needs to be dropped 0.6mm.
At BDC we will now have effectively 0.6mm of radiused piston timing edge sitting above the duct floor.
As testing would indicate , if this is done power increases , so maybe the reduced effective port area has a downside , but this is swamped by the flow increase factor.

As my testing has discovered , the boost port flow regime is a bigger issue.
What I believe happens is that as the boost port is severely angled upward the flow going over the radius attaches to the piston and is pulled downward - directly increasing short circuiting
by changing the leaning tower angle away from the rear wall.

One solution is to cut the piston radius using a dividing head , and stopping the radius cutter just short each side of the boost port.
But this changes the boost port timing , as now the cylinder has been dropped to suit all the other ports.
Another solution is to lift the boost port floor upward well above BDC , so the flow column doesnt have a chance of attaching during the bulk flow period around BDC.

I have not had a chance to actually try either of these options in a back to back test.
The result of simply radiusing the piston and dropping the cylinder is a good increase in power up the front side , but overev directly after peak is diminished alot more - maybe not an issue for many
but NFG for a KZ.

[skako]

My suggestion on how to measure the effective height of the port, for any piston position.
Prof. Jante tested the roundness of the piston edge on a 2-stroke diesel engine type NZD 12.5.
Jante determined that the optimal radius of rounding of the edge of the piston is about 5.5% of the cylinder diameter.
This should be taken into account when looking at the drawing.
The dimensions in the drawing are only for better understanding.

[Jan Van Hamme]

My suggestion on how to measure the effective height of the port, for any piston position.
Prof. Jante tested the roundness of the piston edge on a 2-stroke diesel engine type NZD 12.5.
Jante determined that the optimal radius of rounding of the edge of the piston is about 5.5% of the cylinder diameter.
This should be taken into account when looking at the drawing.
The dimensions in the drawing are only for better understanding.

I had seen in Frits' tips and concepts that the radius had to be 5% of the stroke. That's how I drew it too.
A combination lock of 10?
...I think my novice radius timing question here is going into Pandora's open box. Where we have to decipher the Davinci code using a cracked enigma machine!

In Engmod2T my RD125LC from 1982 (199°/129,4°/YZ125reedvalve) with a non radius timing edge reaches 34.5HP at 11000rpm.
I think I would do well to try to put that into practice first.
Through a reinforced coupling and a self-balanced and aligned crankshaft with silver-plated bearings and a solid lightened VHM 110mm conrod, maybe with ceramic main bearings, an Italkit PI.01.58A.V2 piston where i make the windows in the same shape as the inlet port,I hope to be able to transfer 31 HP to the ground without breakage.
If that works, I will be extremely satisfied.

[husaberg]

In 1963... I was -7 years old. (Born december 1970)


An accountant....;)

[Jan Van Hamme]

An accountant....;)

No, not an accountant.
I have a bachelor's degree in mechanical design and production technology.
That's nothing compared to an accountant.
Late at night, slumped in the sofa after about 3 "Rochefort 10" beers, I can no longer count whether there were 3 or 4.

[Frits Overmars]

My suggestion on how to measure the effective height of the port, for any piston position.
Prof. Jante tested the roundness of the piston edge on a 2-stroke diesel engine type NZD 12.5.
Jante determined that the optimal radius of rounding of the edge of the piston is about 5.5% of the cylinder diameter.
This should be taken into account when looking at the drawing. The dimensions in the drawing are only for better understanding.Excellent, Skako. So you have Jante's books too? For those who are curious now: "Über Verbrennungsmotoren und Kraftfahrwesen, Band 2" by professor Alfred Jante.
It won't be easy to find those books now, but if you manage to do so, please let me know; there is still a volume missing in my library.

The research on of the exhaust top edge radius, page 333 and subsequent, shows that Jantes NZD 12.5 research engine had a bore of 90 mm and a stroke of 125 mm.
My research into the effects of the bore/stroke ratio led me to make the radius dependent not on the bore, but on the stroke, and I found an optimum at 5% of the stroke.
354006

[Frits Overmars]

If both the piston and the exhaust port have a timing radius, and if both radiuses are not tangential to the bore, and if the top of the exhaust port has an elliptical shape, then calculating the open port passage degree by degree for the purpose of determining the angle.area becomes quite a job. Thank god for computers.
354007

[Jan Van Hamme]

Excellent, Skako. So you have Jante's books too? For those who are curious now: "Über Verbrennungsmotoren und Kraftfahrwesen, Band 2" by professor Alfred Jante.
It won't be easy to find those books now, but if you manage to do so, please let me know; there is still a volume missing in my library.

Frits, I found this one.

[skako]

Excellent, Skako. So you have Jante's books too? .....


Yes Frits, I have that book on my desk. I saw her for the first time in 1985. I was looking for her for many years. I managed to get it 8 years ago.
Guys, forgive me for my (creative) mess. I know it's not a virtue. I am interested in everything and bring everything to the table. But it is my work corner where I enjoy it in my own way. Only my wife resents me very much for that.
But which man is perfect in life?

[Frits Overmars]

Frits, I found this one.Thank you very much Jan. I've got Band 2 here but am still looking for Band 1. I will contact them and see what they've got.

[Frits Overmars]

Yes Frits, I have that book on my desk. I saw her for the first time in 1985. I was looking for her for many years. I managed to get it 8 years ago.Your book is in better shape than mine, Skako. You wouldn't happen to have two copies of Band 1, would you? :innocent:
354014

[skako]

Your book is in better shape than mine, Skako. You wouldn't happen to have two copies of Band 1, would you? :innocent:


I'm sorry I don't have band 1.
Band 2 is the only one I have from Jante.

[Jan Van Hamme]

Thank you very much Jan. I've got Band 2 here but am still looking for Band 1. I will contact them and see what they've got.


Maybe Band 1 from this other website ? I don't know how Band 1 looks like.

[skako]

I'm sorry I don't have band 1.
Band 2 is the only one I have from Jante.


Excellent, Skako. So you have Jante's books too? For those who are curious now: "Über Verbrennungsmotoren und Kraftfahrwesen, Band 2" by professor Alfred Jante.
It won't be easy to find those books now, but if you manage to do so, please let me know; there is still a volume missing in my library.

The research on of the exhaust top edge radius, page 333 and subsequent, shows that Jantes NZD 12.5 research engine had a bore of 90 mm and a stroke of 125 mm.
My research into the effects of the bore/stroke ratio led me to make the radius dependent not on the bore, but on the stroke, and I found an optimum at 5% of the stroke.
354006
On page 319, the exhaust duct has a large radius drop that is approximately 78% of the cylinder diameter, at an angle of about 35° to the horizontal plane. The large radius on the upper edge of the port transitions into a smaller radius that is about 11% of the cylinder diameter.
These ratios are according to my approximate estimation based on the data and drawings that can be seen in book Band 2.
Sorry, I did something wrong with these double repeats.

[Frits Overmars]

Maybe Band 1 from this other website ? I don't know how Band 1 looks like.Thank you once more Jan. I am going to try that.

[Pursang]

If both the piston and the exhaust port have a timing radius, and if both radiuses are not tangential to the bore, and if the top of the exhaust port has an elliptical shape, then calculating the open port passage degree by degree for the purpose of determining the angle.area becomes quite a job. Thank god for computers.
354007

Reminiscent of the significant improvement in flow that can be achieved by using multiple angle cuts on poppet valves and seats.
https://www.k20a.org/attachments/valve-1-jpg.9963/

[F5 Dave]

If both the piston and the exhaust port have a timing radius, and if both radiuses are not tangential to the bore, and if the top of the exhaust port has an elliptical shape, then calculating the open port passage degree by degree for the purpose of determining the angle.area becomes quite a job. Thank god for computers.


Oh he absolutely hates them. They have helped disprove his existence multiple times and you don't even want to know the logical logistics for him to even form that opinion.

[Frits Overmars]

Reminiscent of the significant improvement in flow that can be achieved by using multiple angle cuts on poppet valves and seats.
https://www.k20a.org/attachments/valve-1-jpg.9963/Watching that image makes me want to cry. What happened to common sense? I can't imagine anyone would want to improve flow by cutting multiple angles on poppet valves and seats. I would leave out the poppet valves completely. I would also leave out the four-strokes completely. But if you insist on four-strokes, imagine the significant improvement in flow that can be achieved by substituting those multiple angle cuts with radiuses.
I happen to know some otherwise decent people who work on four-strokes, so I'm not completely unaware of what goes on there. Radiusing is common practice in competition four-strokes and has been so for a number of decades.

[wobbly]

Yes Frits , radiused geometry is now commonplace since Rottler introduced multiple axis CNC porting machines with spindle cutting heads that can also form any shape in the seat area.

[SwePatrick]

Just some info of my tzr250 i´m converting to fuelinjection.
It isn´t by far finished in dyno(mapping) but it seems very promising, a lot of wheelspin halters my progress, but i´ll change the tire for the coming weekend(reduce slip).

But i wanted to share with you the gains of having a seriously short intake compared to normal.
In my case the normal intake with carburetor was about 130mm long.
It is now only 35mm long.

And in picture below, in the white quadrant there wasn´t any power before, it just fell on it´s nose after ~11500rpm, at 12000rpm i had about 5-8hp left, now it is above 50hp.
And i haven´t really lost anything in midrange and on the left side of the curve, i can´t say exactly as it is slipping on the dyno.(maybe after this coming weekend i got more info on that)
I also marked with a red arrow some slight misifre i had, probably due to not 100% correct fuelmap yet, it was worse at first, but after some pulls when i richened it up in steps, it started to go away.
If probably is just adding some more fuel in that area it will go away, and maybe some more hp.
But my tire was melting so i had to end the dynoday.
IR gun said the tire was 82-85c hot, it was very 'wet' when i laid my hand on it, i actually got stained black *lol*
Best before ending it was 71.4hp, i have dynoed more with carburetors.
That was with a lot less wheelslip, so probably it is equal now, but i can´t say just yet.

I will when i feel i am very close, mount the wideband sensors and finetune it.

Best of all, rock solid idle and lowrpm drivability, really smooth.
And idles perfect from cold to hot, and coming down to idle perfect after some hard pulls on dyno.

Very pleased so far =)

354018

[SwePatrick]

Watching that image makes me want to cry. What happened to common sense? I can't imagine anyone would want to improve flow by cutting multiple angles on poppet valves and seats. I would leave out the poppet valves completely. I would also leave out the four-strokes completely. But if you insist on four-strokes, imagine the significant improvement in flow that can be achieved by substituting those multiple angle cuts with radiuses.
I happen to know some otherwise decent people who work on four-strokes, so I'm not completely unaware of what goes on there. Radiusing is common practice in competition four-strokes and has been so for a number of decades.

I need to argue with you Frits.
You are not always correct.
Radius seats are commonly NOT used due to wet flow do not like it.
In exhaust you can use it.
I´ve been porting foulstroke heads on a very serious level for about 5-6yrs ago and further back in time.
I often reached the same levels of power as professionals did, this with my 'hobbylevel' of knowledge.
On turbocharged engines i often reached far more power, or to say it otherwise 'the same power' but at far less boostpressure.

The idea of not having radiused seat on intake is that you need those abrupt corners between the different faces to keep the fuel atomized and suspended in air column.
It has been verified many many times in motorsport.
We can take Pro stock in dragracing, 8liter V8 with poor technology is reaching more power per litre than many highly tuned engines with 4valve technology.
And the tuners all agree there, you need those non radiused seats.

Dry flow is an another thing though =)

[Pursang]

Yes Frits , radiused geometry is now commonplace since Rottler introduced multiple axis CNC porting machines with spindle cutting heads that can also form any shape in the seat area.

Multiple angle cuts were obviously not optimum but were a means to achieve some consistency in multiple cylinders with manual machining operations. It was more about the similarity of the image than the finer details.

As wobbly says, Four Strokes now have 5 axis CNC porting machines. The valve pocket and tract is not too hard to imagine as a transfer port or exhaust duct.
https://www.chevelles.com/attachments/tfs175cnc1-jpg.732006/

If 'precision' radiused port openings and piston edges are able to produce valuable improvements in flow volume and directional control a Computer controlled tool would allow quick and consistent experiments and/or performance upgrades to production units.

[aljaxon]

spent the last few days searching this thread and i like the idea of a two stage header with wobblys 2/3 1/3 dimensions but am struggling to fit in the 3.5/5.5 angles along with a 3 stage diffuser with a sharper angle last cone to give more front side power. if i try and incorporate all this and the 32/68%
my belly goes too large in diameter. over 3.5x my duct exit diameter. 25mm . i cant have the main diffuser more than 12 degrees. and even then my last diffuser isnt much steeper.
can i use a two stage header but with angles 60% of the recomended @ 2.1/ 3.3 ? that only saves me a fraction.
or can i ignore belly diameter and my diffuse sections would go 8-12-18 degrees and follow roughly the lengths of the various pipes ive seen on here. wobblys wr200 pipe layout seems similar to my needs except it doesnt have the steeper
last diffuser
my rear cone im guessing a bit less by 2 or 3 degrees. 22.

aiming for wide power emphasis on front side.

i can make 3 pipes with variations and see how they perform on the dyno.

[wobbly]

As with all of the results gained from the black art of pipe design everything is a compromise and no free lunches are available.
To gain front side I would go with a slightly steeper single stage header say 4* with a two stage diffuser , making the second cone quite long and steep.
But 18* is very steep in any mans pipe design manual ,so I think shooting at that number is too limiting , if a smallish center section is deemed desirable.
Why the emphasis on a pipe with a narrow belly , this is only mandatory in old engine designs with lift shaft transfer ducts and no inner radius to keep the transfer streams on track,
away from the Exhaust port.

EDIT - SwePatrick , just a couple of observations re your SportsDevices printout.
Why is there a ratio difference with the two files shown ?
The DIN700 correction is useless for a 2T - JIS D1001 is far better or the latest update V41 has the FOS correction option that works very well.
Your graph is showing either you do not have enough trigger teeth to give enough data points for better resolution , or you have very low smoothing in operation - no way does
an inertia wheel jerk from rpm to rpm point like that.
Here is a sample run off my SportDeviced rig - it has 124 teeth on a starter ring gear 1:1 with the wheel , and minimal smoothing.

[SwePatrick]

away from the Exhaust port.

EDIT - SwePatrick , just a couple of observations re your SportsDevices printout.
Why is there a ratio difference with the two files shown ?
The DIN700 correction is useless for a 2T - JIS D1001 is far better or the latest update V41 has the FOS correction option that works very well.
Your graph is showing either you do not have enough trigger teeth to give enough data points for better resolution , or you have very low smoothing in operation - no way does
an inertia wheel jerk from rpm to rpm point like that.
Here is a sample run off my SportDeviced rig - it has 124 teeth on a starter ring gear 1:1 with the wheel , and minimal smoothing.

Different days, different gears(front sprocket, and also slip), i thought that was obvious as the name of the runs kind of hinting on that =)
But upcoming weekend it will sadly enough differ again as i´m about to change rear rim and tire to a known good kombo that doesn´t melt on the roller :blink:
I do run quite low smoothing as i want to se small changes in fuel and ignition map, running more smoothing just lowers the numbers very little, up to only ~1hp.
And this isn´t any hunt for most hp in the world at this point, so i don´t need to be 100% correct, i only need to see changes.

I´m not a fan of FOS compensation as it is the one that adds the most power, but i also need to say i actually haven´t studied what to use, i only just chose the one that a friend of mine runs in he´s cardyno and settled with that.

I´m running if i remember 16 tooth on the triggerwheel at the roller, (the one that was included).
Earlier i had Performancetrends system and it never showed what you mention even though i just had one triggerpoint per revolution.
And about v4.1, it is actually quite buggy.
You can also spot there is no torque reported, i later on loaded the runs into v4.0 and it showed torque, so it was recorded, but not presented in v4.1.

But i also got a starterring, so i might test that in the future. :niceone:

[SwePatrick]

A little video of me just not getting it(to start with) :laugh::laugh::facepalm:
I have my excuses, but i won´t drag them to the surface here :)


https://www.youtube.com/watch?v=W_a7x64mMB4

[TZ350]

313065313064

This exhaust port floor dam gave a very positive result on the dyno but the cylinder was written off before I could finish the experiment. An exhaust port floor dam is something I am defiantly going to include in my next motor.


We Know for a fact that on a 54.5mm stroke race engine lifting the Ex floor several mm made more power.
It was tested properly in a real back to back by Mr Thiel.
Blindly thinking lifting it more will automatically be better is a dangerous assumption, and could well end up like most assumptions
in just being an error waiting to be revealed.
Sure a longer stroke would need alot more, but how much has still actually to be tested properly.
TeeZee tested it on a cylinder that was a good one, he buggered that up in some way, then added a high floor or dam and made it better.
Not very conclusive or scientifically relevant to a non buggered up cylinder.

354021

There was some talk about razed exhaust port floors.
This is Team ESE's attempt. Alloy insert shaped to the exhaust duct floor. Retained by screws and sealed with high temperature epoxy.
It worked well enough, certainly didn't have any catastrophic negative effects on performance like so many of our other out of the box ideas have done.
Was it better, yes it looked like it but hard no know definitively. It showed promise. If it was easy I would do it again.
The hand dug side ports worked out Ok too.
We eventually destroyed this cylinder trying to improve it, as you do.
The pursuit of one off special cylinders that take a lot of work were abandoned by the team as replicating them for other team members was not practicable.

[aljaxon]

As with all of the results gained from the black art of pipe design everything is a compromise and no free lunches are available.
To gain front side I would go with a slightly steeper single stage header say 4* with a two stage diffuser , making the second cone quite long and steep.
But 18* is very steep in any mans pipe design manual ,so I think shooting at that number is too limiting , if a smallish center section is deemed desirable.
Why the emphasis on a pipe with a narrow belly , this is only mandatory in old engine designs with lift shaft transfer ducts and no inner radius to keep the transfer streams on track,
away from the Exhaust port.



thanks for the reply wobbly, i appreciate your help. re the 18° i saw an r1 pipe design of yours on here with a last steep section of 24° and just dumbed it down a bit and plucked 18 out of the air. skip to last bit if you want to ignore my ramblings ***

re narrow belly, if i use the same angles as 125/200cc pipes my 25mm start diameter grows to 100mm or more. remembering your tz750 that wouldnt run well with 100mm
ive only just noticed this that smaller start diams grow much larger proportionatley despite using the same angles.
2t calc blair and frits suggest less than 3.5 x start diameter for the belly. this ensures that smaller start diameter pipes = lesser header diffuser angles.
to use the same angles on my 25mm my pipe will have a much larger pipe volume to cyl volume.
i need to research this.


******
it was messing with my head but then i looked at it this way. i start at 20mm smaller diameter than a 125cc pipe. and using the same angles i carry on always being 20mm behind. so a 130mid section on a 125 pipe i am 110mm. or if 130 is only for race bikes a 120 mid i am 100mm.

and im only 74.6cc's

so can i use the same angles?

[aljaxon]

with those angles i get a belly of 113.8. thats sticking to 32% 68% good or bad?
https://live.staticflickr.com/65535/53336689772_f08b5e6a05_c.jpg

purely by searching through all this threads millions of pages and cherry picking stuff which is said to work well this is the pipe i'd love to build.
but i know how it works. in real life there will be one or two major flaws in the design which no matter of clever fancy ideas can override. still at 32% 68%
https://live.staticflickr.com/65535/53337805413_c3ecdb75bd_c.jpg

[Frits Overmars]

....2t calc blair and frits suggest less than 3.5 x start diameter for the belly.I did? Damn, I really did. And it's only 45 years ago so it must be state of the art :p.
354023
A belly diameter of 2.9 times the initial diameter was incredibly fat at the time. The predominant response was "He's crazy".
Oh well, that was also said when I preferred a large crankcase volume to a small one and a low compression ratio to a high one.




















​

[aljaxon]

about as up to date as me....

ive never seen anyone suggest that 4.5 x could work and thats what mine would be if i stuck to those angles.
ive only just realised that the 3x or whatever belly factor dictates smaller angles on smaller diameters. amongst other factors.
and thats why i previously quoted the belly factor as if it mattered because on all the calcs or software ive used it only refers to that as opposed to actual angles.

ive searched on here but cant find anything to tell me at what point too much pipe volume/cyl volume is bad.

i see it referred to on pipe dimension diagrams but no explanation.

i prefer low pressure nowadays. im on 5mg of ramipril.
maybe i could put some into my fuel tank?

[jonny quest]

Aljaxon, your center section doesn't need to be straight.

Put some taper in it to get the diffuser and tailcone angles you want.

[aljaxon]

yeah thanks johnny quest, ive noticed that looking at some of the designs on this thread

but that would be throwing yet another variable into an already cluttered mix.
im thinking my rear cone is steep enough for what i want?

but i will remember that for a future design.

its for a road bike where cruising needs more front end power and maybe a wider power band?

ive just made a turntable for my welder and am impatient to get a pipe designed so i can see how my welds will improve.

[wobbly]

Looking at extreme examples and taking those as useful guides is a doomed exercise. The R1 pipe design took 3 months of continuous simulation/build/dyno time to achieve what was the most powerful
current 125 race engine on the planet , the TZ750 had the worst port/duct geometry ever conceived and was instantly overscavenged at the drop of a hat by anything even approaching an aggressive pipe.
Both tell you nothing of any use in a somewhat properly designed small modern roadbike scenario.

Back to basics - a 24* rear cone , no matter how fat the pipe , is going to suppress overev in a small roadbike to the point that you would need to shorten the TL so much , all the front side will be lost.
If your porting layout is done somewhat properly then the 3 to 3.5 belly is just fine as with a long TL and the 32/68% points in place , then all the angles will be shallow by nature.

One of the lessons I have learned is that a very strong arbiter of a powerband fit for the end use , is a combination of Exhaust timing and TL that achieves superposition to increase power where its needed most.
There is an infinite number of combinations , but quite a narrow band of useful ones that achieve superposition at a chosen useful rpm.
The old guide of using around 192* of Exhaust duration also just happens to give a wider range of useful combinations.

Same with the intake tuned length , usually the 3rd harmonic is the most practical combination of length that will fit , and effectiveness.
But of course both these effects can only be compared in a good simulation code.

[JanBros]

A belly diameter of 2.9 times the initial diameter was incredibly fat at the time. The predominant response was "He's crazy".
Oh well, that was also said when I preferred a large crankcase volume to a small one and a low compression ratio to a high one.
​

and when you proposed a reedvalve in the top of the piston, they loved it :killingme

[Frits Overmars]

and when you proposed a reedvalve in the top of the piston, they loved it :killingmeYeah, that was a great April Fool's joke :clap:

[Wos]

Al, it would be a shame if our paths parted in this way. But the aspect in which the FOS exhaust concept distinguishes itself most from other concepts is the determination of the initial diameters. And if those are too large in an existing cylinder, you have just two options: throw it away or apply an insert, like Wobbly just wrote. In almost all cylinders you can do that without changing their outer appearance.

Looking back at my contributions I found this picture of a KTM 50SX cylinder with a clearly oversized standard diameter, and of the same cylinder with an insert.
This picture is over ten years old and I posted it in KiwiBiker, Pit-Lane, Facebook and four other forums, so there has been ample opportunity to find it.
I know it's nearly impossible to check everywhere, but you must realize that it's totally impossible for me to tell every questioner where to find the answer to every question.
That is your own responsibility.
​Keep asking questions, but also do your own research so you won't have to repeat every mistake I and others have made in the past.
353967 353966


HELLO Frits,

Our Rotax 124 cylinder has a exhaust diameter of 41,5 mm🙃🤣

Welding is to risky as cylinders are hard to find and very expensive...

So we like to do a insert to reduce to about 35.

Please give us some advice

Which is best way to go and avoiding overheating of the insert.

Shrink ist in? Glue it with jb weld?

Which aluminium alloy for the insert?
Something like the diecast Alu of the cylinder?

Thanks Frits! 😀

Vielen Dank
Grüße

Wolfgang

[Frits Overmars]

Our Rotax 124 cylinder has a exhaust diameter of 41,5 mm. Welding is to risky as cylinders are hard to find and very expensive. So we like to do a insert to reduce to about 35. Which is best way to go and avoiding overheating of the insert. Shrink it in? Glue it with jb weld? Which aluminium alloy for the insert? Something like the diecast Alu of the cylinder?
WolfgangA very light shrink fit would be best, combined with some heat resistant glue if you wish. I'll leave the choice of material up to you.
But I have a different suggestion: if Rotax 124-cylinders are expensive and hard to find, you might think about using a modern kart cylinder.

[Wos]

A very light shrink fit would be best, combined with some heat resistant glue if you wish. I'll leave the choice of material up to you.
But I have a different suggestion: if Rotax 124-cylinders are expensive and hard to find, you might think about using a modern kart cylinder.

Thank you Frits

Think we try aluminium alloy with hi silicium, with equal heat behavior

The classic enduro reglementation Frits🙄.
Have to stay with watercooled

Are there aircooled modern available rotax in kart sports?

Job on the crank is done Frits, wobbly etc😃...3 mm less in diameter...radius for better flow😉👍

Frame is all complete ...waiting for rotax 124🤩

Grüße Wolfgang

[wobbly]

Frits is right , counterbore the cylinder with a light press fit - you dont need any glue , the insert will be located in the duct by the step and cant move outward as its retained by the flange face.
Been there done that , it works perfectly.
Edit , the insert can also be only welded around the exit face on a spigot type duct - I have done that as well with no issues.

[Wos]

Frits is right , counterbore the cylinder with a light press fit - you dont need any glue , the insert will be located in the duct by the step and cant move outward as its retained by the flange face.
Been there done that , it works perfectly.
Edit , the insert can also be only welded around the exit face on a spigot type duct - I have done that as well with no issues.

Thanks wobbly and frits

Light shrink or press fit will give best heat transfer👍...but only with small tolerances and perfect shape, when there is realy no gap between..

Other idea to use thermal paste in addition...it is ressistant up to 230 celsius degree...

Thanks again!👍

Grüße Wolfgang

[Wos]

Hi Together,

This is the original works shape of disc valve inlet duct. Oval like a egg.

Isnt it better to open and close suddenly? Like i sketched on the housing?

Merci danke thanks..

Wolfgang

[Wos]

Hi Together,

This is the original works shape of disc valve inlet duct. Oval like a egg.

Isnt it better to open and close suddenly? Like i sketched on the housing?

Merci danke thanks..

Wolfgang

[wobbly]

That shape gives the max intake area if that is needed , but the disc closing edge badly wears the case.
This is due to the fast air column pressing on the shutting area.
To fix this you need the closing edge on the disc angled forward so that the outer radius keep longer contact with the case surface.
I will find a picture and post it.
This configuration has no effect on power with the same closing timing.

The best shape is to reduce the boss diameter on the disc and have the longest width on crank centerline - and or increase the disc diameter.
This reduces the port width and gives greater STA for the same timings.

[Wos]

That shape gives the max intake area if that is needed , but the disc closing edge badly wears the case.
This is due to the fast air column pressing on the shutting area.
To fix this you need the closing edge on the disc angled forward so that the outer radius keep longer contact with the case surface.
I will find a picture and post it.
This configuration has no effect on power with the same closing timing.

The best shape is to reduce the boss diameter on the disc and have the longest width on crank centerline - and or increase the disc diameter.
This reduces the port width and gives greater STA for the same timings.

Ok wobbly...if we need ...top answer!

Think wee need quick force on mass in rotax dammed snorkel??...and maybe a softer closing could be have two positiv effects...more guidance...and a lower/ softer...time shifted...bounce
Back of the mass in snorkel?...

Thank you very much !!

Grüße

from disc valve beginner Wolfgang

[wobbly]

Dont even think about damn snorkels , its not physically possible to make a RV intake too short using a normal carb even with Frits insert O Ring idea.

[TZ350]

That shape gives the max intake area if that is needed , but the disc closing edge badly wears the case. This is due to the fast air column pressing on the shutting area. To fix this you need the closing edge on the disc angled forward so that the outer radius keep longer contact with the case surface. I will find a picture and post it. This configuration has no effect on power with the same closing timing.

354033 354034

Picture of an RSW250 rotary disk and the other where Frits points out the error of my ways.
The disks rotate anti-clockwise in these pictures.
You can see the beginnings of wear on the rounded closing side of my disk. There was corresponding wear on the closing edge of the crankcases' inlet port.

[Wos]

Ok wobbly...if we need ...top answer!

Think wee need quick force on mass in rotax dammed snorkel??...and maybe a softer closing could be have two positiv effects...more guidance...and a lower/ softer...time shifted...bounce
Back of the mass in snorkel?...

Thank you very much !!

Grüße

from disc valve beginner Wolfgang


Dont even think about damn snorkels , its not physically possible to make a RV intake too short using a normal carb even with Frits insert O Ring idea.

Good morning wobb and tz

Thanks for tips and warnings:clap:


I know frits idea with a kind off "guidance bar". Is it that what you call o-ring?

We have a enduro. Boots of rider aside motor covers :brick: ...no space to mont carb on disc cover directly

But we are talking about low revs for enduro use... a overrev to 10500..11000 ...

Am i wrong with my theory, that faster opening helps to accelerate mass quicker in fucking long :mad::motu: missconstruction
:nya: to fill crankcase faster??

Thanks for your help and advice :cool:

Grüße Wolfgang

[Frits Overmars]

I know frits idea with a kind off "guidance bar". Is it that what you call o-ring?
354037
This is the bronze inlet disk guidance bar.

.
354038
This is the ultra-short carb mounting with the O-ring O.

[Wos]

354037
This is the bronze inlet disk guidance bar.

.
354038
This is the ultra-short carb mounting with the O-ring O.

Very short frits... top...thank you

Clutch cover...disc side has height of 85 mm... mikuni 34 about 78 length...6 mm for gap between airbox and carb to breeth... have calculated this:niceone:
Its possible...

But need to cut off part clutch cover...do oilsealing it...its of Magnesium...do complete new channel to airbox...all bullet proof to airbox ... folks... sorry not this winter :rolleyes:
Have patience with us please:not:

And let me please ask if it would help open suddenly...


Grüße Wolfgang

[wobbly]

Short answer about the angled straight sided port , yes it does make a little more power .
I tested all this at ZipKart when the 256 first came out - dozens of valve opening and closing shapes and must of been a hundred timing combinations.
Once we had the straight port sides we couldnt go back , but even with the angled closing side on the valve it never really solved the wear issue.
Not worth the small increase in power in my opinion.

[Wos]

Short answer about the angled straight sided port , yes it does make a little more power .
I tested all this at ZipKart when the 256 first came out - dozens of valve opening and closing shapes and must of been a hundred timing combinations.
Once we had the straight port sides we couldnt go back , but even with the angled closing side on the valve it never really solved the wear issue.
Not worth the small increase in power in my opinion.

Hey wobb...thank you

Be sure that we have things in mind that are worth to do:wings:

Lite piston
Welding head to built a squish area
Reduce ex duct
Changing transfers to more upward
Max ex duct to 70 percent and 30 blowdown
New nikasil coating
Build a pipe
Programming a ignition curve

A lot to do as we only meet every possibe friday:woohoo: :cheers:

Viele Grüße to all

Wolfgang

[TZ350]

354050 354051 354052

For something different. The dyno drum had become worn smooth allowing the bikes wheel to spin up more easily than it should.

It had been a problem for a while. Taking the drum out and re knurling it seemed like an impossible task.

Today the Laser guy came and started to restore the traction surface of the drum by deep etching it.

The surface now has the same grippy feel to it that it had when new. A Laser! Who would have thought!

Amazing technology. It can engrave in different colours and even QR codes below the surface of the stainless top layer so the design stays stainless clean for ever.

Lots of other normal engraving tricks too. For effects like, deep or through engraving to just removing a layer of paint or anodising to reveal a logo or design.

It was just a chance encounter that we heard about this. It took only a couple of hours start to finish to restore the dyno drum. Great value.

[F5 Dave]

Great stuff Rob. I had the same issue on 'my' (Vash's) dynojet. Was showing up on my 100hp RZ so resorting to deep clean and ultimately tightening the straps a bit more than ideal. Not my problem (or Mike's, RIP dude) anymore.

[Strokerhaus]

354037
This is the bronze inlet disk guidance bar.

.
354038
This is the ultra-short carb mounting with the O-ring O.

This must be an Ultra Ultra short carb mounting, this is a Gardner carb built into an Armstrong disc valve cover. It was also done on a Barton I believe.
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=354056&d=1701166875&thumb=1&stc=1

[Frits Overmars]

This must be an Ultra Ultra short carb mounting, this is a Gardner carb built into an Armstrong disc valve cover. It was also done on a Barton I believe.
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=354056&d=1701166875&thumb=1&stc=1Yes, you cannot do much shorter than that.
But Armstrong only got away with it because the Gardner carb does not have an integral float that would have been severely confused by vibrations.

[Flettner]

Yes, you cannot do much shorter than that.
But Armstrong only got away with it because the Gardner carb does not have an integral float that would have been severely confused by vibrations.

Inlet can be shorter, with no carburetor and sliding throttle 'Gibs'.

[SwePatrick]

Inlet can be shorter, with no carburetor and sliding throttle 'Gibs'.

My intake is just 32mm long =)

Follow my work on youtube in post below this.

[SwePatrick]

Part two of my tzr 250 injection project.

Please press like and subscribe. :niceone:

Part three will be last part in this series, i´ll add nitrous in that one, aiming for ~100ps to the tire. :devil2:


https://youtu.be/A1MBeJX_WFI

[pete376403]

Inlet can be shorter, with no carburetor and sliding throttle 'Gibs'.


Kevin Cameron used, because it was much shorter, a Tillotsen carb on the 350 Bighorn racer he built.

[Frits Overmars]

Inlet can be shorter, with no carburetor and sliding throttle 'Gibs'.Yup. And with your transfer port injection you won't have float vibration problems either.

[lodgernz]

Interesting History:
http://www.classic50racingclub.co.uk/The-Piovaticci-Racing-Motorcycles/

[Gradella23]

Hello everyone,
I'm finishing the design for my next cylinder. It's a Honda nsr 125 racing cylinder, it'll be produced both for 110mm and for the original 104mm conrod.
Now, i have some doubts about the right place to put the water entrance: in the original engine, the water enters on the right side of the cylinder base, and exits all the way up over the head.
This is not good imho, cause the cool water is immediately in contact with the hot exhaust duct, and not with the transfers for which I've made also an inner cooling duct.
Considering that there is no flow from the basement, and that to be adaptable to the original engine we cannot reverse flow, where is the best place to enter given my colling design?
I was thinking about a spigot as low as possibile on the rear center of the cylinder base, with the exit on top of the head on the front side.

[beta]

Hello everyone,
I'm finishing the design for my next cylinder. It's a Honda nsr 125 racing cylinder, it'll be produced both for 110mm and for the original 104mm conrod.
Now, i have some doubts about the right place to put the water entrance: in the original engine, the water enters on the right side of the cylinder base, and exits all the way up over the head.
This is not good imho, cause the cool water is immediately in contact with the hot exhaust duct, and not with the transfers for which I've made also an inner cooling duct.
Considering that there is no flow from the basement, and that to be adaptable to the original engine we cannot reverse flow, where is the best place to enter given my colling design?
I was thinking about a spigot as low as possibile on the rear center of the cylinder base, with the exit on top of the head on the front side.

come geometrie dei travasi c'è ancora molto margine a vedere le foto, per l'acqua dentro l'intradosso per far le cose fatte bene ci vuole l'intradosso grosso, così prendi due piccioni con una fava e migliori pure le sezioni. I booster la parte iniziale è migliorabile un bel po'

[wobbly]

I agree , having the cold water enter at the boost port , go around BOTH sides of the transfers ( not just a small hole ) right down to the deck to cool the case surface as well, then forward to the Exhaust duct.
Exit is into the head above the Exhaust port , across the head and out above the boost again.
I have done this on several old TZ engines by adding a copper gasket or weld on spacer plate to force flow thru the cylinder first.
They used to run at 70*C or more , but with a widened pump impeller running at 50* is normal.

Edit - I have been trying for years to get TM to take the cold water from between the gearbox /crankcase and take it forward over the mains , then up each side of the boost port.
Having measured it , the transfer entry area under the cylinder, each side of the crank is bloody hot.
Having water in the case under the Exhaust means you can also bleed a small amount around the duct that can then exit upwards to the head - again keeping hot water away from the transfers.

[Gradella23]

come geometrie dei travasi c'è ancora molto margine a vedere le foto, per l'acqua dentro l'intradosso per far le cose fatte bene ci vuole l'intradosso grosso, così prendi due piccioni con una fava e migliori pure le sezioni. I booster la parte iniziale è migliorabile un bel po'

ciao, cosa intendi con geometrie dei travasi?
il condotto dell'intradosso può essere sicuramente allargato, ci devo lavorare, a maggior ragione volendo entrare da dietro. Sui booster intendi la geometria del condotto o il raffreddamento?



I agree , having the cold water enter at the boost port , go around BOTH sides of the transfers ( not just a small hole ) right down to the deck to cool the case surface as well, then forward to the Exhaust duct.
Exit is into the head above the Exhaust port , across the head and out above the boost again.
I have done this on several old TZ engines by adding a copper gasket or weld on spacer plate to force flow thru the cylinder first.
They used to run at 70*C or more , but with a widened pump impeller running at 50* is normal.

Edit - I have been trying for years to get TM to take the cold water from between the gearbox /crankcase and take it forward over the mains , then up each side of the boost port.
Having measured it , the transfer entry area under the cylinder, each side of the crank is bloody hot.
Having water in the case under the Exhaust means you can also bleed a small amount around the duct that can then exit upwards to the head - again keeping hot water away from the transfers.

Hello wobbly, i read your previous comment on the matter, thanks for the contribution.
Ok so having no flow from the crankcase the best option remains the rear cylinder base entry i sketched above, with enlarged inner transfer duct, am i right?

[Flettner]

Building a water cooled version with powervalves next. Quick and dirty, cast the cylinder then weld an aluminium jacket around it. Water cooled crankcase also.
This direct air cooled one has done two events now, trouble free.

[wobbly]

Yes enlarge the duct inner tunnel , but the water is a long way above the transfer tops as well , can you add a water channel around the outside , right down to the deck to cool
that as well.

[TZ350]

.
Special long stroke (44mm) RG50 crank with 95mm rod and big bore kit. Aiming for a turbocharged and fuel injected rotary valve 69cc RG.

354071 A 354072 B

Ok, lets see if I have got this balance factor thing right this time.

A = 147.8g
B = 71.5g

(B/A)*100 = BF

BF = (71.5/147.8)*100 = 48.4%

Ok, so currently its a little less than 50%. So I need to add weight to the counter ballance or drill some holes on the big end pin side.

[jbiplane]

Installed mesh in reed valve housing to dont allow broken petals damage engine
https://reaa.ru/attachments/mesh-jpg.543592/
Seems should not affect power

[F5 Dave]

Is that a real problem? Especially with Fibre based reeds.

[Pursang]

Is that a real problem? Especially with Fibre based reeds.

Operating hours will be low for drones flying to targets in Ukraine!

[F5 Dave]

Ooh. Too soon. :sweatdrop

[TZ350]

.

354081 354082

Something interesting on the dyno today. 92% unbridged exhaust port.

[TZ350]

.

Ok the 92% cylinder is not the one for the scooter but this home made cylinder has been successfully run in competition.

354085 354086

The cylinder uses a small tongue to guide the trapped "L" shaped ring back.

354084

The exhaust port floor forms a dam that starts about midway up the transfers.

[TZ350]

.

354087 354088

Transfers have removable covers and the transfer windows are CNC machined so that they are radially and angularity are symmetrical and match each other.

So for those wondering if screw top pistons, trapped "L" shaped rings and exhaust port floor dams are real. Then this is one cylinder where these features have been made to work.

[TZ350]

354050 354051 354052

Today the Laser guy came and started to restore the traction surface of the drum by deep etching it.

354089

Laser etched finish on the dyno drum. Tested it today, it seems to work, great restoration method for old DynoJet dyno drums.

[jbiplane]

I produce engines for amateur aviation, for customers like this https://www.fulcrum-engines.com/

Is that a real problem? Especially with Fibre based reeds.
I had a problen when at -28C original Moto Tassinari V-Force carbon petal in the center were broken and made some further damages.
It happen at 6 hours 40 minutes of permanent work at 6700rpm. It happen first time, but I very offset and dont want it happen again.
I will try make 0.4mm kevlar petals as instead of carbon in this valve.

[Pursang]

I produce engines for amateur aviation, for customers like this https://www.fulcrum-engines.com/

So does this Company!

354091

This looks like a 'business' opportunity!

354090

Slava Ukraini!

[Pursang]

I had a problen when at -28C original Moto Tassinari V-Force carbon petal in the center were broken and made some further damages.
It happen at 6 hours 40 minutes of permanent work at 6700rpm. It happen first time, but I very offset and dont want it happen again.
I will try make 0.4mm kevlar petals as instead of carbon in this valve.


-28C is the air temperature at 4000m., assuming a ground temp of around 0C. (like say.. mean Winter temp in Ukraine)
Specified operating altitude of a Shahed drone is 60 - 4000m.


I really hope I'm just a bit paranoid, but Russia's brutal and criminal assault on Ukraine Must Not be supported.

Slava Ukraini!

[TZ350]

354092

https://www.facebook.com/photo/?fbid=10161171465454322&set=a.41107369321&__cft__ (https://www.facebook.com/photo/?fbid=10161171465454322&set=a.41107369321&__cft__)[0]=AZXHmmgugPPjH36MU_QhfYvUjFJkaV_rD7IjwFlHO7BE2BSF8 W3WNAy-aByy-ojUy3VBdvoPTz-B6vvXWO8E5uZXbjEX4aGKd5sm_tMKsbjbBIuPSzLb3CvtcPJqX t6aGEWfPzqpSule3_Be9d7BHgeBzhe2zCfwX8N5RjWlGDKC3o6 gzJ30BBxrrHhhSVdZroJn8ZbPmj8gIZ91v5NOBtxS&__tn__=EH-y-R

Lets not point the finger at each other but save it for the politics that shook the jar and got the ants fighting.

[flyonly]

I have a friend who is having problems with a yz250 based kart engine running on methanol. Peak up is at 9250. This is the ignition curve he has. 354093
I think it’s too much and does not drop off.

He had melted pistons. Egt is getting to 620

An I on the right track to help him?


Sent from my iPhone using Tapatalk

[Frits Overmars]

I have a friend who is having problems with a yz250 based kart engine running on methanol. Peak up is at 9250. This is the ignition curve he has. 354093
I think it’s too much and does not drop off.kWith 'peak up' you mean maximum power? Then the ignition timing is more than 10° too early there.

[flyonly]

Yes. Peak up is meant to be peak hp. Dumb auto correct


Sent from my iPhone using Tapatalk

[wobbly]

The ignition is way too advanced , but that can be corrected by reducing the static setting - such that you get 15* at peak HP rpm.
But besides that issue , any engine that sees over 600* egt on Methanol is WAY too lean and WILL seize immediately.

[SwePatrick]

Depending on compressionratio 15degree might be low try ~17-18degree if having oem compressionratio.
BUT!! richen it up a LOT!
I´ve seen best results with methanol at ~430degree exhaust temp.
And by doing this you probably need to build a new pipe to get the peak at the same rpm.(shorter pipe for methanol engines)

[Wos]

I have a friend who is having problems with a yz250 based kart engine running on methanol. Peak up is at 9250. This is the ignition curve he has. 354093
I think it’s too much and does not drop off.

He had melted pistons. Egt is getting to 620

An I on the right track to help him?


Sent from my iPhone using Tapatalk

Seems to be a hpi ignition curve.

This cdi is available with second curve..switchable

But these universal cdi curves never fit perfect to application...

Also available for hpi inner rotor ignition are free prgrammable cdis

Or you use yamaha original ignition rotor stator and combine it with hpi cdi programmable for original yamaha ignition system..:woohoo:


Yz 250 original curv is only 20- 23 advance to 4000 then falling... reason seems to be to keep it rideable:msn-wink:

Next game changer was to reduze squish gap from about 1,8 mm to 0,9 within keeping compression ratio...area 50 percent... :cool:


Grüße Wolfgang

[41juergen]

Seems to be a hpi ignition curve.

This cdi is available with second curve..switchable

But these universal cdi curves never fit perfect to application...

Also available for hpi inner rotor ignition are free prgrammable cdis

Or you use yamaha original ignition rotor stator and combine it with hpi cdi programmable for original yamaha ignition system..:woohoo:


Yz 250 original curv is only 20- 23 advance to 4000 then falling... reason seems to be to keep it rideable:msn-wink:

Next game changer was to reduze squish gap from about 1,8 mm to 0,9 within keeping compression ratio...area 50 percent... :cool:


Grüße Wolfgang

Why don't you use a Zeeltronic or Ignitech, both are programable and you can adopt them to all needs...

[flyonly]

Why don't you use a Zeeltronic or Ignitech, both are programable and you can adopt them to all needs...

I am suggesting that. Maybe you can help with a related question. The flywheel has a magnetic pickup. Can these work with Zeeltronic and Ignitech? The kart has no battery so it would need to be an AC unit with an internal reg/rec. just not sure about the pick uphttps://uploads.tapatalk-cdn.com/20231205/8629b9fb1601ddc2990345ea89069abb.jpg


Sent from my iPhone using Tapatalk

[Peljhan]

You have programmable unit for PVL and Selettra available from Zeeltronic.
https://www.zeeltronic.com/page/psr-p01.php

Supported generators:
- PVL 50ohm stator 1424, 58mm rotor
- Selettra P3356, 60ohm stator, 58mm rotor

https://www.zeeltronic.com/page/psr-p02.php
Supported generators:
- PVL 50ohm stator 1419, 1424
- PVL 171ohm stator 1443

I don't know compatibility with HPI ignition

[wobbly]

That HPI analogue ignition has around 8* retard from 6000 to 9500.
So if it is statically retarded to give 15* at 9500 there will be 23* at 6000.
If you run 18:1 compression that Methanol will be happy with in a watercooled ( been there , done it , works perfectly ), then there is nothing wrong with that ignition curve across most of the powerband.
I dont know what sort of power the ignition puts into the gap , but if its even marginal then a fine wire plug like a R7376-11 will help.
The next step of course is to run a P2 Ignitech paralleled to double the CDI energy with the same volts.

[flyonly]

Wobbly

Can you get a magnetic pickup that works with that stator and the ignitech. I am more used to the lump of steel on the flywheel that acts as the pickup


Sent from my iPhone using Tapatalk

[Wos]

Hello together :Punk:

Hpi inner rotor programmable cdi works without battery dc

Zeeltronic says

USER MANUAL
PSR-P02 PROGRAMMABLE CDI IGNITION
PSR-P02 is programmable CDI and is specially designed to work with PVL ignition
with inner rotor. It does not work with original PVL ignition coil and require ignition coil
for CDI ignitions. PSR-P02 also requires small 9V, or 12V battery. Current draw is
very low and it is about 25mA when engine running. Small 9V block battery is enough
for more than 10h operation, when shift light and power jet are not used.

??? Bad for long distance endurance races:wait:⅜

Why take another manufacturer?
Are ignitech or zeeltronic cdi better, more advatages in programming???

I ask this for my fellow ... he used hpi analog this year and he wants to go next step forward :yes: programmable for next race

[yatasaki]

I am suggesting that. Maybe you can help with a related question. The flywheel has a magnetic pickup. Can these work with Zeeltronic and Ignitech? The kart has no battery so it would need to be an AC unit with an internal reg/rec. just not sure about the pick uphttps://uploads.tapatalk-cdn.com/20231205/8629b9fb1601ddc2990345ea89069abb.jpg


Sent from my iPhone using Tapatalk
Throw away that Chinese made "ignition" and get yourself hpi or selletra .
Save yourself time and pistons, only thing that is usable here is HPI rotor machined for pvl stator.
Severa independentl race applications went disaster after exactly one year of installing/using this ignition.
Ignition curve goes berserk usually on prolonged wot (straights)

[Wos]

Throw away that Chinese made "ignition" and get yourself hpi or selletra .
Save yourself time and pistons, only thing that is usable here is HPI rotor machined for pvl stator.
Severa independentl race applications went disaster after exactly one year of installing/using this ignition.
Ignition curve goes berserk usually on prolonged wot (straights)


Ups...even hpi is not without damages...

The 210 series with light...outside rotor collapsed with new inner stator on our enduro at coil for timing...ääh...fuck...2 dissapointing races in 2 weeks :(... ficken !



Please...give us answer which parts in special...which ignition went to disaster... and why ...sorry...not clear to me...

Try to avoid every Desaster in long lasting races

Thanks

Wolfgang

[TZ350]

.

Two strokes >104cc in the F4 Bucket racing class here in NZ are restricted to the equivalent area of a single 24mm carb.

Team ESE did a lot of work to improve flow through their 24mm carbs.

And recently someone did some comparative flow tests for us using a 28mm Keihin as a standard comparator.

354096

28mm Keihin (3) flowed 23.2 CFM
24mm venturi insert (1) glued in the back of a bored out 24mm OKO. Gave 94% flow of the 28mm Keihin.
24mm OKO (4) with a std 24mm throat but the down side flared out to 28mm. Gave 86% flow of the 28mm Keihin.
24mm unmodified standard Suzuki GP125 carb (2). Gave 78% flow of the 28mm Keihin.

[F5 Dave]

Rob, I don't understand 1. The bellmouth appears cut off. The insert is long?
Is there any tapering?

[wobbly]

I have always thought running a PVL or Selettra stator with the Zeel was a Mickey Mouse solution , as you are using the existing HV source coil.
These are always compromised as the wire size and turns are limited to gain enough spark voltage , not ignition power.
The best solution be it a Zeel or Ignitech is a proper DC-DC converter , using a 12V generating stator.
TeeZee does a mod stator winding - but I think the best solution is an early 2000 rotor/stator off CR Honda MX 125/250 that had electronic powerjets and some had a
12V PV servo as well. Driving a reg/rec to give 14.2V charging thru a cap or battery.
These can be adapted onto near anything , as its a very common taper 1:10 . I even put one on a TZ400 twin with two triggers @ 180* off the single rotor lobe.

[TZ350]

Rob, I don't understand 1. The bellmouth appears cut off. The insert is long? Is there any tapering?

The insert is my best interpretation of a venturi. The lead convergent cone is aerofoil shaped. The constriction is 24mm and the tail is an energy recovering divergent cone. Like the X section of an aero wing.

The insert is glued and pressed in. It can't be removed from the carb body without wrecking the carb.

The insert is about 40mm long and the inlet tract to the rotary valve is about 68mm. The carb was enlarged in the area of the main jet to reduce the disruption to the airflow by the slide, Jet nozzle and needle.

The part of the bell mouth that was there for the air filter rubber boot, was cut off.

354097354098354099

This class legal 24mm OKO that has been modified, gives 94% of the flow of a genuine standard 28mm Keihin.

It is probably time to do away with the 24mm carb rule. No other F4 bike has that restriction.

[F5 Dave]

I've found that front face important to flow as the carb sucks right around corners apparently. I've made rounded slip ons like a finger to cover the air-boot part but make the area circularish in cross section, with small gains on the dyno. Kneedit built up on shown would be an easy test.

[Grumph]

How big was your bored out OKO?

I used a 29mm flatslide carb off an RG250 with an insert on the engine side which was shaped as you've done - but only about 15mm long

Never flow tested it but results were pretty good.

[TZ350]

How big was your bored out OKO?

24mm OKO was bored out to 28mm. It carbureted Ok. But when I tried this trick using bigger carbs like 38's there was an immediate flat spot if I whipped the throttle wide open quickly. Not very useful, but not a problem with the OKO.

[yatasaki]

Ups...even hpi is not without damages...

The 210 series with light...outside rotor collapsed with new inner stator on our enduro at coil for timing...ääh...fuck...2 dissapointing races in 2 weeks :(... ficken !



Please...give us answer which parts in special...which ignition went to disaster... and why ...sorry...not clear to me...

Try to avoid every Desaster in long lasting races

Thanks

Wolfgang
Sorry I typed to purchase hpi or selletra instead of PVL or selletra.
HPI 068k012& k017 in particular

[aljaxon]

i am needing a bit of an explanation of what starts to happen at the point where the belly changes into the rear or baffle cone.

to my thinking this is when the stuffing waves start returning to the cylinder. lets say tuned length is 9000rpm so these "start" waves at 9000rpm will be returning well before ex port closing. and they will return at ec well over the peak 9000 lets just say 12000rpm. could be a lot higher but its not the point.

and how do i get the "start waves" to not return so high rpm or so early at 9000rpm . my logic is to have a longer belly. but to retain the tuned length then the rear cone gets a sharper angle. and at some point too sharp is no good.

there is something im obviously missing. or is the rear cone just a compromise? in the old days thinking was that the rear cones midpoint was the tuned length so you had a bit of cone before and after to give you decent waves either side of peak power. but having the end of the cone for the tuned length there doesnt seem to be any cone physically to give you decent waves below peak rpm.

apologies for being a retard




.

[Wos]

Sorry I typed to purchase hpi or selletra instead of PVL or selletra.
HPI 068k012& k017 in particular

Ok yatasaki

Owner of hpi told us to outer rotor...there are problems with overheating when they are covered.
And he told...inner rotor hpi should be more ressistant to heat...

But what the hell we could do in enduro with water and mud...for 6 hours

Now installed hpi inner rotor...and the rider told...significant mor power as never before...same ignition timing...
Ok...that was at last race this year...lets see next year:rolleyes:

Wobbly!

Thanks...thaught about a solution with old crosser ignitions...that coils seem to be undestroiable ;)


And for newer Generation of crossers there are plug and Play programmables from hpi we are very happy with...squish...carb and map and you are in ballpark of factory bikes :niceone:


Grüße Wolfgang to all

[wobbly]

Luckily the explanation is simple , so any retard can get it.
Yes the rear cone used to be a compromise , with a single angle the mid point of the full uncut conic is the mean reflection point.
Not that that was any help to anyone , but that's the physics involved.

But if you want to reduce the reflection amplitude whilst the piston is dropping , or around BDC . then its a simple matter of reducing the cone angle.
Then later , as the piston is rising , reducing the port area , we can now increase the cones efficiency by increasing its angle - as the pipe surface furthest away is effective later and later in the waves
time signature.
Take this to the logical extreme and you get parabolic curved shape .
This was first used mid last century in clever designs , made of spun sheet metal , used in KT100 clutch pipes - way way before some clever dick thought to use the simpler multi angle approach.

Nowdays we can easily approximate the parabolic shape , with a 3 angle rear , and test first a single angle to confirm the TL , then beat the hell out of that in EngMod with three angles.
In that painful iterative process you can very accurately adjust the peak , and drop off angle after peak power , by the length and angle of the last steepest section.
The length and angle of the first two sections sets the ramp up shape of the front side power potential.

In this design I did for TM , I spent 3 months looking for the best combination of front side ramp and slow overev angle - made excruciatingly hard due to no PV and a straight line ignition.

[Frits Overmars]

what starts to happen at the point where the belly changes into the rear or baffle cone.
to my thinking this is when the stuffing waves start returning to the cylinder. lets say tuned length is 9000rpm so these "start" waves at 9000rpm will be returning well before ex port closing.Yes, hopefully. Otherwise the waves couldn't do much good, could they?


then... the rear cone gets a sharper angle. and at some point too sharp is no good.You've got that right, Al.


in the old days thinking was that the rear cones midpoint was the tuned length...In the old days thinking was also that the earth was flat. Every change in cross flow area causes a reflection, that is to say: over the entire length of the cone. The fact that in those old days people assumed the wave to start from the center of the cone, or, even more daft, from the middle of the total length of the imaginary end cone extended to zero diameter, was just an aid to form a mental picture (pun intended).

[skako]

Hello everyone,

several ignition timing simulations. Model C9 has variable time. Model C21 has a fixed time of 22° which can be seen in the attached pictures.
Model C9 and C21 at 9000 RPM have the same ignition time. All other model settings are the same for all models shown.
It is not clear to me, at 9000 RPM both models should have the same power.
The power graph would have to overlap or intersect each other at 9000 RPM? That's not the case here?
Maybe I didn't set the model right?
Can someone clarify this for me?

354101354102354103354104

[wobbly]

Haha Frits , the only mental picture I get from you saying " aid " is marital.

[wobbly]

Skako, the sim is calculating the pipe bulk temp in real time as the rpm points progress.
It cannot suddenly change the accumulated results at one specific rpm , unless you only run that one rpm individually and overlay the two results.
Thus what was happening directly before 9000 is affecting that result - just as would happen in reality.
Neels may have a better logic than mine here.

Two things to note - its absolutely impossible to run 95 Unleaded at 13:1 , I use 11.75 A/F ratio and that's pushing it hard.
Even 110 Octane would struggle to not detonate at 13:1 when making serious power.

Also you have not run the sim in Turbulent mode , then created a new Combustion Model from that run , with the real Delay/Duration and Vbe numbers that are affected by Compression/MSV/ timing and A/F etc
specific to your setup.
You enter the new saved Combustion file parameters , and then continue in Prescribed - its also way faster.
Just running the generic inputs can lead you well down a blind rabbit hole of non reality - again.

EDIT - running 22* of advance at peak power the thing will absolutely destroy itself , so something else is seriously wrong for the screen to not be screaming DETONATION at you during a sim run.

[F5 Dave]

In the old days thinking was also that the earth was flat. . .

Well I don't want to spoil Christmas for anyone
But Santa isn't real
. . . either is Jesus.

[TZ350]

.


Well I don't want to spoil Christmas for anyone but Santa isn't real.

354105 but the Xmas Elf is real... right!

[husaberg]

.



354105 but the Xmas Elf is real... right!

354108354106354107
why yes....

[Wos]

Hello everyone,

several ignition timing simulations. Model C9 has variable time. Model C21 has a fixed time of 22° which can be seen in the attached pictures.
Model C9 and C21 at 9000 RPM have the same ignition time. All other model settings are the same for all models shown.
It is not clear to me, at 9000 RPM both models should have the same power.
The power graph would have to overlap or intersect each other at 9000 RPM? That's not the case here?
Maybe I didn't set the model right?
Can someone clarify this for me?

354101354102354103354104

My personal picture is that all involved parts...cylinder, piston, head and pipe act as a storage of heat that was produced by all the parameters of combustion...so a change of ignition timing never can result in a complete sudden change of egt temperature... like maybe wanted...expected...predicted

So in a optimum ignition timing for specific arrangement, especially pipe....there has always to be a delay, for heating up or cooling down the egt...???

Am i right...or wrong? specialists here???:wait::wait::clap:

[skako]

I was thinking of testing with an electric Prony brake, where power (torque) can be accurately determined at constant RPM.
An accurate electric Prony can hold a loaded engine for 5+ minutes at exactly 9000 RPM. Then the influence of too hot or too cold exhaust pipe is no longer there. The gas mass flow is uniform throughout the entire engine with all gas dynamics within the exhaust pipe.
Why I mention Prony. Prony is a static brake at a constant RPM, while the Dyno test has to measure it in 1-2 seconds when the RPMs have already escaped to higher where we have new conditions.
If at a constant RPM the input parameters are the same, then the output result should be the same for all..
With due respect all, I think Vannik sees something more.

[aljaxon]

Luckily the explanation is simple , so any retard can get it.
Yes the rear cone used to be a compromise , with a single angle the mid point of the full uncut conic is the mean reflection point.
Not that that was any help to anyone , but that's the physics involved.

But if you want to reduce the reflection amplitude whilst the piston is dropping , or around BDC . then its a simple matter of reducing the cone angle.
Then later , as the piston is rising , reducing the port area , we can now increase the cones efficiency by increasing its angle - as the pipe surface furthest away is effective later and later in the waves
time signature.
Take this to the logical extreme and you get parabolic curved shape .
This was first used mid last century in clever designs , made of spun sheet metal , used in KT100 clutch pipes - way way before some clever dick thought to use the simpler multi angle approach.

Nowdays we can easily approximate the parabolic shape , with a 3 angle rear , and test first a single angle to confirm the TL , then beat the hell out of that in EngMod with three angles.
In that painful iterative process you can very accurately adjust the peak , and drop off angle after peak power , by the length and angle of the last steepest section.
The length and angle of the first two sections sets the ramp up shape of the front side power potential.

In this design I did for TM , I spent 3 months looking for the best combination of front side ramp and slow overev angle - made excruciatingly hard due to no PV and a straight line ignition.


thanks for that wobbly. i got almost all of that. I saw that R1 pipe design on here when i did a big search. it uses much shorter header and end of diffuser percentages than the 32 68 that i am using for the current front end pipe design
i suppose i can make a pipe with a straight rear cone and then a couple with different angled parabola's and dyno them and go from there. ive always done a single angle rear cone and split it for ease of fabrication. having 3 different cones will make rolling them much simpler, and im no longer scared of welding. before i used to shy away from it and tried to avoid extra seams/joints.

[aljaxon]

Yes, hopefully. Otherwise the waves couldn't do much good, could they?

You've got that right, Al.

In the old days thinking was also that the earth was flat. Every change in cross flow area causes a reflection, that is to say: over the entire length of the cone. The fact that in those old days people assumed the wave to start from the center of the cone, or, even more daft, from the middle of the total length of the imaginary end cone extended to zero diameter, was just an aid to form a mental picture (pun intended).


the earth is flat.
especially where i live. in fact its concave. and i assume you live/lived just across the north sea from me in the land of spetters? (very memorable (for more than one reason) dutch biking film) cant get much flatter than that.

i thought having the strongest stuffing wave returning just before ex port closure was best. sort of like halfway between transfer closure and ex port closure.
but the waves that occur at the start of the rear cone return far too early or at the desired time but at a much higher than peak rpm. those waves arent wanted if you dont want over rev. so im thinking why not have a much longer belly? purely in the case of my situation wanting little overev and more front side power so as to be able to cruise without tap dancing on the gear lever.

[skako]

Skako, the sim is calculating the pipe bulk temp in real time as the rpm points progress.
It cannot suddenly change the accumulated results at one specific rpm , unless you only run that one rpm individually and overlay the two results.
Thus what was happening directly before 9000 is affecting that result - just as would happen in reality.
Neels may have a better logic than mine here.

Two things to note - its absolutely impossible to run 95 Unleaded at 13:1 , I use 11.75 A/F ratio and that's pushing it hard.
Even 110 Octane would struggle to not detonate at 13:1 when making serious power.

Also you have not run the sim in Turbulent mode , then created a new Combustion Model from that run , with the real Delay/Duration and Vbe numbers that are affected by Compression/MSV/ timing and A/F etc
specific to your setup.
You enter the new saved Combustion file parameters , and then continue in Prescribed - its also way faster.
Just running the generic inputs can lead you well down a blind rabbit hole of non reality - again.

EDIT - running 22* of advance at peak power the thing will absolutely destroy itself , so something else is seriously wrong for the screen to not be screaming DETONATION at you during a sim run.

ok wobbly,
now I see, the simulation should go in several steps and not as I did in just one step.
I am new to using this simulator, still learning how to use it properly.
Thanks wobbly for pointing out my mistake.

[wobbly]

Wos , absolutely correct about the hysteresis in the temp system.
That sort of answers the next point for Sako - most tuners use inertial or Eddy dynos with constant load for testing of 2T engines specifically as it emulates
the very dynamics we see on track.
That is , more power = more acceleration.

We never , ever see 9000 rpm for more than a split second after getting off the gas and down changing into a corner.
The pipe temp has dropped in that period and then what happens on the dyno , happens on the track - we give it full throttle.
Thus a good sim on petrol will reflect this with a wall temp of near 325*C at the bottom of the powerband , then if the dyno run time is correct , we will see the wall temp the
pipe sees on the track at full noise - around 425.

This is not the egt as seen in the header , that is affected by the A/F ratio used and the combustion parameters ( Compression/MSV/Timing ) and this influences the pipe bulk gas temp
that ultimately affects the wave speed just as much as the pipe wall temp does.
This pipe wall temp on petrol has been proven very accurate in many sims from 50cc to 300cc - but only if a realistic A/F ratio is used for the fuel.

I can see no useable benefit at all to doing step and hold testing of a 2T - doing correctly timed dyno runs simulates reality - just as we are trying to do with a sim.

And Al , you have a serious Catch 22 with belly length - make it longer and that generates a steeper rear cone , sure that limits overev , but even more so it affects negatively the front side power.
Once again my favorite saying , sorry - no free lunch.
And as I have already said , that R1 pipe tells you nothing apart from the 3 cone rear setup, as its designed to generate max power spread from 10,000 to 14800 from an engine with no PV , no PJ
and is limited by a flat line ignition.

[aljaxon]

Wos , absolutely correct about the hysteresis in the temp system.
That sort of answers the next point for Sako - most tuners use inertial or Eddy dynos with constant load for testing of 2T engines specifically as it emulates
the very dynamics we see on track.
That is , more power = more acceleration.

We never , ever see 9000 rpm for more than a split second after getting off the gas and down changing into a corner.
The pipe temp has dropped in that period and then what happens on the dyno , happens on the track - we give it full throttle.
Thus a good sim on petrol will reflect this with a wall temp of near 325*C at the bottom of the powerband , then if the dyno run time is correct , we will see the wall temp the
pipe sees on the track at full noise - around 425.

This is not the egt as seen in the header , that is affected by the A/F ratio used and the combustion parameters ( Compression/MSV/Timing ) and this influences the pipe bulk gas temp
that ultimately affects the wave speed just as much as the pipe wall temp does.
This pipe wall temp on petrol has been proven very accurate in many sims from 50cc to 300cc - but only if a realistic A/F ratio is used for the fuel.

I can see no useable benefit at all to doing step and hold testing of a 2T - doing correctly timed dyno runs simulates reality - just as we are trying to do with a sim.

And Al , you have a serious Catch 22 with belly length - make it longer and that generates a steeper rear cone , sure that limits overev , but even more so it affects negatively the front side power.
Once again my favorite saying , sorry - no free lunch.
And as I have already said , that R1 pipe tells you nothing apart from the 3 cone rear setup, as its designed to generate max power spread from 10,000 to 14800 from an engine with no PV , no PJ
and is limited by a flat line ignition.

cheers wobbly
i started thinking i can fiddle with multi different angled rear cone sections to get the one that matters shallower. like an initial sharp angled cone followed by a shallower cone. but then i suppose the initial sharper cone would rob too much of the available energy?
only way i can think to do anything is is to have a longer belly but with a narrow diameter to reduce that the rear cone angle. so all my diffuser angles need reducing. also maybe a slowly tapering belly?

im getting a bit too trigger happy now cos i need to get the sections ordered from the laser cutters in time for me to play over christmas.

[wobbly]

Rear cones with a steep initial angle that then flattens our are useless , been there last century - no breakfast or free lunch.
Saw that as a recommended example in an iterative sequence recommended by the Mota simulation package - they obviously havnt actually built one as it for sure doesnt work.
Yes , tapering the belly to reduce the rear cone works - the R1 has that feature as does the R2

[Wos]

Hello wobbly,

With programmable ignition we try to produce cold egt with high retard to force pipe resonance begin as soon as possible...


For me i recogniced that its alwasys a gamble were to stop this high retard and lowering it as this is necessary to avoid Detonation risk
Every engine Konfiguration has diffrent behaviour...

So far found non rule...for a first curve it has been always a shoot from the hipps...if i had a pipe with resonance peek 8500 took 5000 ...from 26 degree to 19 in 500 reve... better falling earlier and deeper to minimize risk for first try

Is there any rule of thumb how much lowering... and were to start?



Thank you very much once again! :)

Wolfgang

[JanBros]

@ Wobbly : you once said that for a CVT +/- 33-67% lengths for header and diffusor are too long, better 30-64%. what do you do with the lost length ? just make the pipe shorter (which seems wrong to me) or add to the belly ?

[wobbly]

Wos - the most useable midrange advance is 30 to 32* and this can be a straight line from around 2000 rpm to the point that the pipe starts to be effective and power is rising sharply
per rpm step . This much static can only be used ( on petrol ) as long as the engine is not run for any extended period in that area - even warming up under load at part throttle.
The next hard and fast rule is that if the compression is optimized for the fuel then its all but guaranteed you will need 15* advance at peak power.
Thus you can draw a straight line from the 30* turnover point to that rpm.
How much retard after peak power depends upon how much overev is needed. Then a flat line prevents excess egt rise that would need richer jetting to cool/ not make power.
The straight line retard can be bent upward into a convex form by looking at the TubMax graph shape and pushing your luck with detonation.

But the logic of using alot of advance to " get the pipe into resonance quicker " seems counterintuitive to me.
The less advance , the hotter the pipe becomes , quicker .
And if you have a port timing/pipe TL pairing that creates superposition within the powerband - the hotter the pipe , the quicker you get into that area.
Sure , pushing the advance gives great throttle response , but Hp wise you are fighting excess compression losses BTDC as the piston is pushing against static compression as well as the quickly rising
combustion pressure , thus slowing down the piston speed driven by only by crank inertia.

JanBros - yes a shorter header pulls down the port negative pressure ratio earlier in the depression cycle , favouring power around peak.
And the shorter total diffuser length gives steeper diffuser angles that favor power around peak. Front side , after the clutch has locked is set by the length and steepness of the
final diffuser , then the rear cone angle(s) will set the amount of useable power directly after peak.

If you use the small duct exit approach with no steps - and a steeply angled slip joint , the peak and overev will be dramatically enhanced , so you the have the choice of either steepening the rear cones to pump up the peak and reduce the overev potential or just lengthening the pipe to get more front side.
In all of this you are manipulating the powerband shape with the cones - all the mid does is to connect the effects together at a specific TL.
Sure it has an effect on pipe volume but imho that is the least useable aspect of pipe design variables - its a by product , not an input.

[Wos]

Wos - the most useable midrange advance is 30 to 32* and this can be a straight line from around 2000 rpm to the point that the pipe starts to be effective and power is rising sharply
per rpm step . This much static can only be used ( on petrol ) as long as the engine is not run for any extended period in that area - even warming up under load at part throttle.
The next hard and fast rule is that if the compression is optimized for the fuel then its all but guaranteed you will need 15* advance at peak power.
Thus you can draw a straight line from the 30* turnover point to that rpm.
How much retard after peak power depends upon how much overev is needed. Then a flat line prevents excess egt rise that would need richer jetting to cool/ not make power.
The straight line retard can be bent upward into a convex form by looking at the TubMax graph shape and pushing your luck with detonation.

But the logic of using alot of advance to " get the pipe into resonance quicker " seems counterintuitive to me.
The less advance , the hotter the pipe becomes , quicker .
And if you have a port timing/pipe TL pairing that creates superposition within the powerband - the hotter the pipe , the quicker you get into that area.
Sure , pushing the advance gives great throttle response , but Hp wise you are fighting excess compression losses BTDC as the piston is pushing against static compression as well as the quickly rising
combustion pressure , thus slowing down the piston speed driven by only by crank inertia.

JanBros - yes a shorter header pulls down the port negative pressure ratio earlier in the depression cycle , favouring power around peak.
And the shorter total diffuser length gives steeper diffuser angles that favor power around peak. Front side , after the clutch has locked is set by the length and steepness of the
final diffuser , then the rear cone angle(s) will set the amount of useable power directly after peak.

If you use the small duct exit approach with no steps - and a steeply angled slip joint , the peak and overev will be dramatically enhanced , so you the have the choice of either steepening the rear cones to pump up the peak and reduce the overev potential or just lengthening the pipe to get more front side.
In all of this you are manipulating the powerband shape with the cones - all the mid does is to connect the effects together at a specific TL.
Sure it has an effect on pipe volume but imho that is the least useable aspect of pipe design variables - its a by product , not an input.

Thank you wob

Spoke in case of low reving oldi classic enduros but also from enduro in general

There we need driveability... torque bevore beinn on pipe...and this is the reason why i stay far under 30 degree...never had needs over 26 degree as drivability was lost ...and we are happy to use the area of reso when its begins to start with "cold" egt... as our pipe is not not long enought ...to short

...after this have to keep too long thing on pipe by hotter egt.. and having some overev by more hot egt

Maybe very contraintuitiv ...as we are limited in exhaust port on oldi 1980 too...

I confirm 15 degree to powerpeak


so my conclusions is... its more difficult to find good timing on 1980 enduro than on some roadracers

On our contests conditions vary...tracks unknown...no Chance to learn shifting points...

But...have another Projekt where your advice will help us for sure in future ;)..a roadracer

Thanks!!!! One more!

Wolfgang

[lodgernz]

We never , ever see 9000 rpm for more than a split second after getting off the gas and down changing into a corner.
The pipe temp has dropped in that period and then what happens on the dyno , happens on the track - we give it full throttle.
Thus a good sim on petrol will reflect this with a wall temp of near 325*C at the bottom of the powerband , then if the dyno run time is correct , we will see the wall temp the
pipe sees on the track at full noise - around 425.

This is not the egt as seen in the header , that is affected by the A/F ratio used and the combustion parameters ( Compression/MSV/Timing ) and this influences the pipe bulk gas temp
that ultimately affects the wave speed just as much as the pipe wall temp does.
This pipe wall temp on petrol has been proven very accurate in many sims from 50cc to 300cc - but only if a realistic A/F ratio is used for the fuel.


Wobbly, this is the first time I have seen any mention of pipe wall temperature.

Would you mind giving us a quick rundown of where to place the sensor, what best sensor, how to interpret results?

[Condyn]

What is the reason why so many championship winning engines seem to end up square, or nearly square? I realize I could spend ages simulating different bore/stroke, port configurations, but the curiosity just struck.

Most of the CVT snowmobile engines I work on are over-square ( short stroke ) so I am asking mainly to get opinions, or more likely facts, on what short comings I am or could be up against with them.

[wobbly]

Lodger , when I asked Neels to add in the option of varying pipe wall temp ( to better simulate reality ) he asked for some actual numbers.
I used a K surface probe clamped onto the outer wall in the mid header , mid body and rear cone end.
These figures from back to back multiple runs re created the egt as seen on track data from the lowest to the highest rpm used , and gave 3 sets of surface numbers.
These then averaged gave 325*C at the bottom of the power band , rising to 425*C after peak power at full throttle.
And when then inputted as actual temps in the sim I got really good correlation for the KZ engine as dynoed and simulated.

I have put these into many , many sims and they have proven to give good baselines for many different applications.
The code uses this input as well as the gas temp generated by all the combustion factors such as A/F , advance , MSV , Compression etc as they all affect actual bulk temp inside
the pipe.

A/F is very important with 11.5 showing good results for unleaded pump and up to 13 for 110 leaded race gas - using compression to suit.
This translates into around actual 620 EGT and 680 EGT for those fuels @ 3X bore from the piston.
If you use the pipe programs from FOS or Neels version in the sim , this also seems to correlate well to between 500*C and 600*C of bulk gas temp throughout the pipe.

[lodgernz]

Wonderful info. Thank you Wobbly.

[wobbly]

A square engine is the best compromise between rpm capability and achievable port time area.
Sure a short stroke can theoretically rev higher , but the piston is heavier so not alot is usually gained.
For the same port timing the short stroke is severely limited in port height despite its larger bore circumferences useable area.

Best example was Yamaha doggedly sticking to 56/50.6 in the TZ all the way up thru the 4DP models - they were completely useless in 125 and 250 GP.
They didnt rev any harder than a square Honda or Aprilia and got their arses kicked Hp wise.
All the way up to 2000 when they finally swallowed corporate pride , bought a Czech anemometric flow visualizer , dumped shit that never worked like twin boost ports , went square
and won first and second in 260GP easily with Jacques.

Sure the Aprilia boys stole points off each other that year , but I was at Philip Island for the final round and the two Yamaha's scrapped over the title right to the finish line -
the whole length of the straight ahead.

[Frits Overmars]

Condyn, Here's a text I happened to have lying around, that might clarify things a bit.

Oversquare is good for four-strokes, where the diameter of the valves that fit into the head is determined by the cylinder bore.
For two-strokes it's the other way around.
I'll give you an example, with a simple rectangular exhaust port, with a port height of 50% of the stroke and a port width of 70% of the bore.
For an engine with 100 mm bore and 100 mm stroke (that's 785,4 cc) this would mean a port height of 50 mm, a port width of 70 mm and a port area of 50 x 70 = 3500 mm².

Let us see what happens when we make that engine really oversquare. We double its bore: 200 mm instead of 100 mm.
But in order to maintain the original cylinder capacity, the stroke must shrink from 100 mm to 25 mm.

Now let's look at that exhaust port again. Its height becomes 50% of 25 mm = 12,5 mm, its width becomes 70% of 200 mm = 140 mm, and its port area becomes 12,5 x 140 = 1750 mm². We've lost 50% of our original port area!

This means that our oversquare engine can rev only half as high as our original engine before running out of breath.
It can produce only half the power of the original engine. Oversquare is not good for two-strokes.

PS Wob, those short-stroke Yamahas were bad alright, but you are doing them an injustice.
From the RD56 onward (my favourite Yam, a simple aircooled twin that beat the mighty six cylinder Honda) the stroke has always been 50.7 mm, not 50.6 mm.

[wobbly]

Yea sorry Frits - Kocinski did it in 1990 and Harada won in 1993 on a 56 by 50.7 , then they were nowhere against the square Honda and Aprilia's till 2000 was my point really.

[Frits Overmars]

Yea sorry Frits - Kocinski did it in 1990 and Harada won in 1993 on a 56 by 50.7 , then they were nowhere against the square Honda and Aprilia's till 2000 was my point really.Point taken and agreed upon. My point was only that the short Yamaha stroke was a whole 0,1 mm longer than what you accused them of :p

[F5 Dave]

Point taken and agreed upon. My point was only that the short Yamaha stroke was a whole 0,1 mm longer than what you accused them of :p
Looser main bearings:laugh:

[husaberg]

Yea sorry Frits - Kocinski did it in 1990 and Harada won in 1993 on a 56 by 50.7 , then they were nowhere against the square Honda and Aprilia's till 2000 was my point really.


Point taken and agreed upon. My point was only that the short Yamaha stroke was a whole 0,1 mm longer than what you accused them of :p

Not that it matters i am Pretty sure the XR79 Kevin won the 93 500 championship was 56mm x 50.7mm.
I am also pretty sure the YZ500 0Wf2 Rainey rode that year before he was injured was also 56mm x 50.7mm.

[JanBros]

JanBros - yes a shorter header pulls down the port negative pressure ratio earlier in the depression cycle , favouring power around peak.
And the shorter total diffuser length gives steeper diffuser angles that favor power around peak. Front side , after the clutch has locked is set by the length and steepness of the
final diffuser , then the rear cone angle(s) will set the amount of useable power directly after peak.


tnx for all your advice.

while trying to design a pipe, my brain short-cutted.
I'm struggling with why the diffuser needs to begin earlier (shorter header). why not just keep the +/- 66-34% , keep the header angle small and make the first diffuser steeper, and maybe make the belly a bit bigger to get steeper angles? isn't it so that the first parts of each sector are for the higher rev's (end powerband) and the last parts for the lower rev's (where the powerband begin's, what you call front side) ? and having the diffuser earlier makes it a bit "out of sync" with the rear cones ?

so what is the advantage off having the diffuser begin earlier ?

[Condyn]

Thank you Wobbly and Frits for clearly painting the picture of why square is better!

JanBros, take what I say with a grain of salt as I am only a hobbiest chump, but a head pipe typically has an angle of between 2-4 degrees and the first diffuser section will be much steeper than that resulting in a more pronounced suction.

Everything I am about to say is talking about my elevator shaft 70s air cooled piston port

On a cvt engine that TRADITIONALLY is tailored for a small amount of front side and mostly peak operating rpm, using a header longer than about 31 percent In my experience ends dismally. With a long header 32-34 there is usually a torque hole in the dyno graph or a double peak before falling off. Not good for a CVT, because if you fall in the hole, there is no getting through it. The header seems to be the most sensitive part of the pipe that sets up everything else. As of late I have been trending towards more shallow headers closer to 3 degrees with good elapsed time field testing results, but still keeping them around 30 percent. I have not dyno tested the more shallow (than my average) headers yet, but if they are working better in the field that is all that matters to me. Maybe the shallow header is helping spread the power out, and maybe that is exactly what is needed in my short duration drag runs where the pipe temp never stabilizes. All of this is just my thoughts and any of it could be dead wrong. I am open to any constructive criticism.

[wobbly]

Its all to do with the distribution of the depressions amplitude before and after BDC.
A shorter header pulls down the depression deeper and earlier between EPO and BDC , gaining peak and overev - but steeper headers seem to work better when longer is needed.
Usual story , this gain is always at the expense of the capability somewhere else.
Then a steeper and shorter first diffuser enhances peak and overev as well.
A steeper and longer last diffuser holds a deeper depression after BDC and just prior to the rear cone removing it all together - enhancing frontside ( power leading up to the peak ).

As the rpm rises the greatest negative pressure ratio amplitude moves rightward , culminating in the deepest portion happening just prior to it suddenly going positive.
At this point there is hardly any amplitude between EPO and BDC
Watching this happen , cycle after cycle on the screen is the only way to actually get a handle on the effects.
The total energy available is finite - so no free lunch.
The Wave viewer that shows the waves amplitude, travelling down the pipe elements in turn is a supremely enlightening use of trickshit science at work , Neels genius code in action.
Learn how to use its powerful visuals.

EDIT - look at the R1 pipe I have published , a very short header with steep first diffuser - pumping up peak and overev , along with a long very steep last diffuser - pumping up late front side.
This gives an engine with no PV , no PJ and a straight line ignition the max achievable from 10,000 to 14,800 with a peak at 13,800.

[Frank S.]

EDIT - look at the R1 pipe I have published , a very short header with steep first diffuser - pumping up peak and overev , along with a long very steep last diffuser - pumping up late front side.
This gives an engine with no PV , no PJ and a straight line ignition the max achievable from 10,000 to 14,800 with a peak at 13,800.

Hi Wobbly,
while looking at the R1 pipe:rolleyes: I wonder what it would look like with a programmable ignition. What would you change? Would you make a complete new pipe or only adjust 1 or 2 parts of it?

[wobbly]

The main factor would be that retard past peak would dump heat into the pipe , thus the TL is way too short and it would rev past the mechanical limit we
have now of 15000.
Changing the TL to at least +25mm would mean every dimension would need to be adjusted to suit the fact that a ton of advance would pump up the mid
and even the rear cones now dont need to worry about limiting overev.
In short - start again.
You got a spare 3 months to sim ,CAD,laser.roll,weld,hammer,dyno,repeat.
Hardest decision is when do you stop.
Here we are 4 years later and it only took three weeks to do the R2 with around + 2 HP - easy.

[Frank S.]

This excessive overreving is exactly what I noticed after using the digital ignition.
But if you extend the TL, doesn't the resonance drop to lower rpms and you lose hp?

[wobbly]

Thats easy - change the Exhaust timing to get superposition ( that is an endless combination set of TL and EPO ) where you want it , to get back the Hp.
Just one of many options available - look at the RSA with a TL of 800 and an effective EPO of 81*, that gave max power at 13000 but it also had a PWM - PJ in play
so the KZ pipe would have to jigged around that issue.
But if you have a programmable ECU then a PWM - PJ is easy if the regs allow it.
Then you may as well add a 42mm carb , a PV and a Rotary Valve - see where this is going.
Jan spent a couple of days on my simulation of the RSA and got 60 Hp , having never used a sim before - see where that is going.

[crbbt]

speaking of 250's and pipes.

Wob, you wouldn't happen to have jig for making pipes for a NX5?

Or any interesting information about?

I am guessing the production racers would have been below your realm :laugh:

[ken seeber]

Gedday. It's been a while.
This discussion on exhaust shape and length is very timely, particularly to myself. For some time (and with many distractions) I have been trying to get the DCI system to show a hint of life. A previous version, which went into the A ports showed it operating, but this was masked by the fact that, around TDC, the port communicated with the crankcase because of the transfer cutout in the piston.

This time it is into the B port, with no such communication.

So, with a normal old style kart exhaust, it does not respond in terms of even a small speed change, irrespective of the nominal rpm set point, ranging from 8 to 14k rpm. I will admit to a totally out of control testing regime in terms of temps and mixture etc.

So, the question is would I be better off with a different exhaust, one that provides a stronger depression around TPO?

I’m convinced it’s gotta work.

354125354124

[diesel pig]

Jan spent a couple of days on my simulation of the RSA and got 60 Hp , having never used a sim before - see where that is going.

I wonder if a lot that power increase was Jan changing the "great leader's" exhaust pipe? I know Jan and Frits were not impressed with his exhaust pipe design.

[wobbly]

I did a NX5 pipe design for a LSR winning project but all that with laser dxf etc info was lost when my dyno laptop was stolen from my workshop.
But I may have a backup on an old hardrive - will have a look over the weekend.

Diesel - part of it was my smaller duct exit and yes , the Leaders pipe was a flawed design that Jan was forced to make work.
His radiused Exhaust timing edge was pure genius at the time , real outside the box thinking.
Its now proven in that an STA analysis of the measured numbers shows the Blowdown lags the Transfers by about 10% - but the added radius would dramatically improve the Cd of the port and
bring it into line without needing port timing increases that would compromise the really effective superposition factor.

[SwePatrick]

Gedday. It's been a while.
This discussion on exhaust shape and length is very timely, particularly to myself. For some time (and with many distractions) I have been trying to get the DCI system to show a hint of life. A previous version, which went into the A ports showed it operating, but this was masked by the fact that, around TDC, the port communicated with the crankcase because of the transfer cutout in the piston.

This time it is into the B port, with no such communication.

So, with a normal old style kart exhaust, it does not respond in terms of even a small speed change, irrespective of the nominal rpm set point, ranging from 8 to 14k rpm. I will admit to a totally out of control testing regime in terms of temps and mixture etc.

So, the question is would I be better off with a different exhaust, one that provides a stronger depression around TPO?

I’m convinced it’s gotta work.

354125354124

Without that little tiny push from crankhouse i doubt you will find any gains.
It might work yes, but no gains.
There is no free lunch :(

[crbbt]

No stress Wob,

Let me know if you have any luck.

I would imagine the pipes would have a pretty serious ignition map, porting and combustion chamber requirements

[aljaxon]

while we are at it has anyone got a pipe design for an rd350A with mild porting?**

i could exchange a load of designs for mobylette 50v's that DONT work :brick:

here's something that has just dawned on me. whenever the waves encounter a convergence in the pipe they send back a stuffing pulse.
so at the very end of the diffuser where the belly starts this will happen no? and at the wrong time? and the more abrupt the change the more energy is wasted?
so, can i "round off" or blend in the diffuser/belly joint to lessen the wasted energy? and again the belly to rear cone seems to me to be returning pulses for the over rev which in my front side cruising pipe is not wanted. if what i suspect is true i can see the advantages of hydroformed/flowing pipes. a short 10mm section either side of the belly could reduce the angles although also increasing the angled cones main angle ever so slightly.


**i made some pipes 10 years ago using blairs percentages slightly tweaked and they have nice power everywhere but no show stopping massive wheelie inducing hit. they go the bike up to 120mph actual. 100 sat bolt upright, which i was pleased with. now geared down to 110 cos im getting old.

glad to see im not the only one asking pipe questions. i previously felt like the pupil in the class always with his hand up - please sir!! please sir!

[JanBros]

waves are created when the diameter changes. at the end of the diffuser the diameter stays the same throughout the belly so no waves are created until the diameter changes again with the beginning of the baffle.

[wobbly]

Where there is no change in CSA there is no wave formation , the belly does nothing.
Except I sometimes use a slightly tapered mid to create an effect needed ( steeper or shallower ) before or after the mid ( up to 3* included )
Yes I have tried a two piece belly like a sharp hump back - no power/no loss.
But the shallow first cone in a 3 cone rear setup does conserve some of the finite wave energy to be made available later down the TL.

Hydro forming causes huge controversy in the pipe community in that some will swear by it , but I spent months at JL learning how to do it " properly ".
The vital part was using steel platens in a press to prevent the larger diameters from blowing out first , and finally I could make real nice looking pieces.
But no matter what , they always lost around 2 Hp to my hand welded cone pipes , on the dyno mule Rotax 125 used to test for the 256 used in Superkarts.
I made a split clamp thing to hold the belly section straight and round and got back 1/2 a Hp.
The smooth transitions between sections always lost 1 1/2 Hp and we ended up having CNC press tools made for just the labor intensive curved header section of the front pipe.
And I noted years later that's how the nice pipes were made on the KTM250GP.
Note the sharp end of the pressed header.

I got to talk to a Honda engineer at Silverstone where we were testing the new ZIpKart one weekend and asked about the split formed pipes they always made.
He said it was done using split female formed tools in an " explosive " process to ensure sharp angles were created.
Lost in translation somewhat , but Boom was the operative word.

[diesel pig]

Hydro forming causes huge controversy in the pipe community in that some will swear by it , but I spent months at JL learning how to do it " properly ".
The vital part was using steel platens in a press to prevent the larger diameters from blowing out first , and finally I could make real nice looking pieces.
But no matter what , they always lost around 2 Hp to my hand welded cone pipes ,

The irony of this is as long as the home hobbyist pays attention to the details when making there pipe, it will be as good as a factory pipe.

[aljaxon]

waves are created when the diameter changes. at the end of the diffuser the diameter stays the same throughout the belly so no waves are created until the diameter changes again with the beginning of the baffle.


its at the point where the diffuser meets the belly and where the belly meets the rear cone. those are the only two angles where any waves created are not wanted. in fact for the first third of the rear cones length im guessing those waves created are wasted on what i want for this front side cruising pipe.

wobblys boom moment noted - re sharp angle changes.

where you want them.

i was told any change in angle would trigger a returning wave. for that reason i was talked out of a twisty curly snail like pipe i'd made. whose many angles would rob energy. you do get told a lot of conflicting info on the net though.

i was told the waves are molecules handing over their energy to adjacent molecules and so on.
to my thinking the molecules on the outside of the diffuser when reaching the belly joint are suddenly forced right left or up down ie off trajectory and are behaving as if the diameter has changed. if not then they are in touch with their cousins 100mm away etc on the other side of the diffuser and have permission to carry on regardless. which seems a bit far fetched. but then again the whole process what happens inside the pipe is almost unbelievable and like magic.

im making one pipe with 10mm blending in sections either side of the belly and one without. plus 3 baffle/end cone combinations for each pipe.

hopefully mr dyno will be happy.

[wobbly]

A change in section area is not the same as a change in directional vector due to a pie cut , as in the second example there is no change in area.
Of course there are limits , and from experience I can say that a pie cut closer than 50mm from the port will affect power.
From observing the wash pattern in the duct it seems that any angle not on the vertical plane creates an asymmetric plugging action on the A/F stored in the duct.
And where a pipe is bent in one plane , like a KZ rear facing one , having the cone seam joints on the outside , looses nearly a Hp to a pipe with all the joins on the inner radius.
I didnt believe it , but was told to do it to the laser pattern .dxf by TM , and yes they were correct - humble pie.
As a general rule having pie cuts greater then 7* ie a 14* bend with 180* rotation will create turbulent eddies and power reduces.
The idea of having a " blending " section in front of the mid belly joint , will simply replicate the construction of a hydraulically formed pipe.
In a race only engine this lost power - but maybe having a slightly longer diffuser is what was needed anyway in a road bike application , and it may in fact be an advantage.

[Vannik]

Strictly speaking, the friction between the gas and the pipe wall also sends a very small positive wave back. This is one of the reasons a very long pipe on a low revving engine never seems as efficient as a short pipe on a high revving engine. A curve in a pipe increases this friction losses and does have an effect although small.

Comparing a blown pipe with an armadillo pipe the armadillo pipe always seem to win by a small amount. My thinking, although unproven, is that the sharp transitions scrub off the developing boundary layer and makes the wave see the full cross sectional diameter and / or minimizes the losses from the friction. How to prove and measure this without a full blown laboratory I do not know.

[philou]

Hello,

how to make search engine work of forum :ar15: ? google no longer works on the site :mad:
I want to display posts as results. there are no results or displays the list of entry topics

[katinas]

Another KTM example of sharp transition between pipe fat sections after pressed or exploded process. Semi mass production pipe from KTM 125 for Red Bull Cup.

[JanBros]

its at the point where the diffuser meets the belly and where the belly meets the rear cone. those are the only two angles where any waves created are not wanted. in fact for the first third of the rear cones length im guessing those waves created are wasted on what i want for this front side cruising pipe.


you keep on reading your own thoughts in other peoples words.
a change in diameter (or better, cross section as Wobbly says, because you could also make a square exhaust) is not the same as a change in angle.

[koenich]

Another KTM example of sharp transition between pipe fat sections after pressed or exploded process. Semi mass production pipe from KTM 125 for Red Bull Cup.

there is also the "real" process of hydroforming, where you have a fullform negative die and a tube is pressed against the walls of the die oooor the parts could be simply deep drawn. both processes (if done properly) have the limitations of bending radius = ~1 x material thickness, so a transistion with t = 0,8 mm sheet metal can be made quite sharp.

[Wos]

there is also the "real" process of hydroforming, where you have a fullform negative die and a tube is pressed against the walls of the die oooor the parts could be simply deep drawn. both processes (if done properly) have the limitations of bending radius = ~1 x material thickness, so a transistion with t = 0,8 mm sheet metal can be made quite sharp.

Somebody talked about forming with explosives Daniel ;) its possible to replikate surface of for example a money coin or even a oak leave absolutely sharp

In german its called " sprengformen or sprengplattieren"

https://de.m.wikipedia.org/wiki/Sprengplattieren

Let us try with your pipe first Daniel? :yes: insert a handgrenade... duck and cover:eek5::done::devil2:


Grüße Wolfgang

[koenich]

Somebody talked about forming with explosives Daniel ;) its possible to replikate surface of for example a money coin or even a oak leave absolutely sharp
i know, i know but doesn't make much sense if standard methods can be applied (or sth was lost in translation). nor does boomforming remove material limits (e.g. minimal bending radius).

[Wos]

i know, i know but doesn't make much sense if standard methods can be applied (or sth was lost in translation). nor does boomforming remove material limits (e.g. minimal bending radius).

Right daniel...not without inside model...

Which sharpness is necessary?


Maybe a grinding job on Welding seam could do ...

[SwePatrick]

Injection progress. =)

I´m having some pleasant issues at the point ;)
The rear swingarm flexes so i loose traction on dyno (fixing that now as we speak)
And still with some 'unhappy' engine i managed to dyno 79.7rwhp(corrected) at 10800rpm, i havent focused so much on drivability yet when mapping the ecu.
I´ll fix that later when snow is gone so i can take it for a drive and log things.

I had issues his summer with the flex also, the chain wouldn´t stay on when we pushed it hard, so it is needed.
I made the swing myself, and might have took it to far with trying to have it lightweight :O

There is more power lurking in this old TZR engine =)
But i said when i´m reaching 80rwhp i´ll start play with my nitrous setup.

I´m aiming for 100rwhp(with nitrous) :D


https://www.youtube.com/watch?v=RQ-P9RlF9Ms

And after looking at the setup i found that an injector was bad. maybe that´s why it misfired so much.
There are some logic to that, the injectors are coming from my Mercedes AMG, i swapped them due to one was hanging open.
And this case, one injector broke, started to leak o fuel on the floor, so i swapped it out.
And maybe i just happened to mount that one that was hanging open.

And why i didn´t flood the engine fully is that injectors maxflow is reached at ~90% throttle at ~10000rpm.
Thats where the secondaries are coming in.
And that´s why it misfired when in low load, and at top where the VE is getting lower.

[aljaxon]

you keep on reading your own thoughts in other peoples words.
a change in diameter (or better, cross section as Wobbly says, because you could also make a square exhaust) is not the same as a change in angle.

janbros you obviously have a problem with me so do us a favour and dont reply if you are not being constructive.

i have questions and would like them answering so as to be able to cut out errors in my already limited knowledge of pipe design.

i could see a sharp angled change in a the pipes sections (although not having a change in cs) still act as if there is a change in cross section.
and that is why i asked if this is so. i was told angles can rob energy hence the disadvantages of too many angles.


andmany thanks to wobbly and Vannik for taking time to offer their help and knowledge.

[F5 Dave]

Please don't take offense, but I believe JanBros was being constructive. The thing about constructive criticism is that it is criticism and it is easy to take offense.

You are obviously strong willed, we are lucky to have some real experts to lend us their time. I think the best approach is to read their posts several times and not try force the answers into preconceived ideas. One should always test theories, sure, but be prepared to give them up if other evidence, or in this case experience of experts, moves the learning forwards into a different environment.

Cheers.

[wobbly]

Al , it must be a nightmare trying to filter the fuckwits out of a technical discussion as you again have the wrong end of the stick.
Quote " i was told angles can rob energy hence the disadvantages of too many angles ".
I can categorically tell you the number of angles ( cuts ) is completely irrelevant.
In fact for achieving the multi plane U bend shapes needed for say a big MX bike , more cuts is better to keep away from the 7* max I advised ie two 3.5* would be way better than one 7*.
Even simply slightly angling up the pipes on a rear facing cylinder , by having 3 small cuts instead of one sharper version - further away from the manifold , absolutely made more power on the BSL500 dyno single.

[pete376403]

Rimar Motors pipework https://www.facebook.com/photo/?fbid=666169042396423&set=pb.100070100006444.-2207520000

[diesel pig]

Al , it must be a nightmare trying to filter the fuckwits out of a technical discussion as you again have the wrong end of the stick.
Quote " i was told angles can rob energy hence the disadvantages of too many angles ".
I can categorically tell you the number of angles ( cuts ) is completely irrelevant.
In fact for achieving the multi plane U bend shapes needed for say a big MX bike , more cuts is better to keep away from the 7* max I advised ie two 3.5* would be way better than one 7*.
Even simply slightly angling up the pipes on a rear facing cylinder , by having 3 small cuts instead of one sharper version - further away from the manifold , absolutely made more power on the BSL500 dyno single.

And this the invaluable Info that this Thread is great for and what was ( I think) F5 Dave was pointing at. It literally saves one from making a dozen different pipes and then working out why one make's slightly move power than the others.

[Vannik]

i have questions and would like them answering so as to be able to cut out errors in my already limited knowledge of pipe design.

i could see a sharp angled change in a the pipes sections (although not having a change in cs) still act as if there is a change in cross section.
and that is why i asked if this is so. i was told angles can rob energy hence the disadvantages of too many angles.


and many thanks to Wobbly and Vannik for taking time to offer their help and knowledge.

Something I wrote a while back, maybe you have not seen it.

354158

[Frits Overmars]

Something I wrote a while back, maybe you have not seen it.Educational and entertaining as always , Neels. Expressions such as 'lift shaft type transfer passages', and 'Armadillo pipe' the other day, make me giggle.
Maybe you can throw in your 'Gasdynamics - Finite Waves vs Sound Waves 101 - Issue01.pdf'. That should keep our enfant terrible occupied during the holidays.
Speaking of which: all the best for everybody :2thumbsup

[Vannik]

Educational and entertaining as always , Neels. Expressions such as 'lift shaft type transfer passages', and 'Armadillo pipe' the other day, make me giggle.
Maybe you can throw in your 'Gasdynamics - Finite Waves vs Sound Waves 101 - Issue01.pdf'. That should keep our enfant terrible occupied during the holidays.
Speaking of which: all the best for everybody :2thumbsup

You mean this one:

354159

[Frits Overmars]

You mean this one:Yup........

[Pursang]

SANTA LOVES TWO STROKES

https://i.makeagif.com/media/12-24-2019/Y16xzH.gif

Seasons Greetings everyone!

[Frank S.]

Something I wrote a while back, maybe you have not seen it.


The more I read here, the more I see that I know less about pipes:wacko:

Merry Christmas to all

[Gradella23]

Thats easy - change the Exhaust timing to get superposition ( that is an endless combination set of TL and EPO ) where you want it , to get back the Hp.
Just one of many options available - look at the RSA with a TL of 800 and an effective EPO of 81*, that gave max power at 13000 but it also had a PWM - PJ in play
so the KZ pipe would have to jigged around that issue.
But if you have a programmable ECU then a PWM - PJ is easy if the regs allow it.
Then you may as well add a 42mm carb , a PV and a Rotary Valve - see where this is going.
Jan spent a couple of days on my simulation of the RSA and got 60 Hp , having never used a sim before - see where that is going.

Fun game this; since we didn't see any 125cc racing product with a 42mm carb since 2011 (besides maybe the 250 superkarts with Aprilia like cylinders), what do you think It should be affected from a cylinder design perspective, taking into account 10+ years of kz2 development that took us over 50hp with fixed Advance, 30mm and fixed compression?
No free lunch Just adding a bigger carb and change the pipe i guess

[wobbly]

But the 'just add a 42mm and change the pipe " scenario would make the engine useless.
Not only in karts where it would have insufficient front side , but in Roadracing where it would need the PWM PowerJet to enable ovrev potential
as the Port/Pipe combination would have to be biased toward front side ( so it had some ) and thus compromising high rpm power.
To make it work it has to have a Rotary Valve as well , and if that is going on its just a modernized RSA.

[Gradella23]

But the 'just add a 42mm and change the pipe " scenario would make the engine useless.
Not only in karts where it would have insufficient front side , but in Roadracing where it would need the PWM PowerJet to enable ovrev potential
as the Port/Pipe combination would have to be biased toward front side ( so it had some ) and thus compromising high rpm power.
To make it work it has to have a Rotary Valve as well , and if that is going on its just a modernized RSA.
But let's Say you have a Roadracing Reed valve, with pj, programmable ignitions and all, there must be something to take advantage of from the last 10 years of progress in cylinders and crankcase beside the improved exhaust duct geometry and cooling.. or maybe It's just been too specific development of the kz regulations and we'd still be stuck with a finely tuned Honda rs like engine? I've heard that good old Gabriele Gnani has reach 55hp lately, no clue how tbh but he doesn't look like an "exaggerate takes" guy

[wobbly]

Yes we can use the developments of the last 10 years if dealing with a reed roadracing engine that has the PV , PJ ,ECU etc.
I have done a 96 4DP Yamaha , I fitted the last -20 cylinders from 99 ( last 56 bore ) and ground all the transfers to change mainly the A port radial and increase their STA
to match the bigger Aux port grinding.
Aftermarket carbon reeds and 40mm HV Lectrons - using the stock PJ solenoids from Yamaha.
With all the latest pipe trickery and programmable Ignitech ECU for the PV , PJ and advance , it made more power everywhere than any of the PVP ,FPA ,DEA Superkart engines had on the same DynoJet
and it made just over 100 RWHp on Avgas ( same fuel as the Rotary Valve engines ).
So I would have to say as the later Yamaha with square bore/stroke was light years ahead of the 4DP even in stock form from the factory , one of those would be easily up at 110 on that same Dynojet.

[Gradella23]

Yes we can use the developments of the last 10 years if dealing with a reed roadracing engine that has the PV , PJ ,ECU etc.
I have done a 96 4DP Yamaha , I fitted the last -20 cylinders from 99 ( last 56 bore ) and ground all the transfers to change mainly the A port radial and increase their STA
to match the bigger Aux port grinding.
Aftermarket carbon reeds and 40mm HV Lectrons - using the stock PJ solenoids from Yamaha.
With all the latest pipe trickery and programmable Ignitech ECU for the PV , PJ and advance , it made more power everywhere than any of the PVP ,FPA ,DEA Superkart engines had on the same DynoJet
and it made just over 100 RWHp on Avgas ( same fuel as the Rotary Valve engines ).
So I would have to say as the later Yamaha with square bore/stroke was light years ahead of the 4DP even in stock form from the factory , one of those would be easily up at 110 on that same Dynojet.
I don't know those engines, was the 4dp the One with 7 transfers? Did you reduce the A Port front Wall radial angle to get it more backwards? I'm usually considering something around 35° as the optimal... How much does a modern kz have?

[wobbly]

4DP was from 91 -99 with 7 transfers yes. The 96 G model ( I think ) A port front wall was 55* from the front to back CL and crossed at about bore center - crazy.
I angled it back to around 1/2 way from bore center to the boost face - still not as steep as the RSA for example.
Modern KZ cross around 1/3 from the boost face to the bore CL.

[41juergen]

4DP was from 91 -99 with 7 transfers yes. The 96 G model ( I think ) A port front wall was 55* from the front to back CL and crossed at about bore center - crazy.
I angled it back to around 1/2 way from bore center to the boost face - still not as steep as the RSA for example.
Modern KZ cross around 1/3 from the boost face to the bore CL.

Hey Wob at what rpm was this, approx. 12.500 - 13000rpm?
Btw: happy new year to all and a good start into 2024!
cheers
Juergen

[Gradella23]

4DP was from 91 -99 with 7 transfers yes. The 96 G model ( I think ) A port front wall was 55* from the front to back CL and crossed at about bore center - crazy.
I angled it back to around 1/2 way from bore center to the boost face - still not as steep as the RSA for example.
Modern KZ cross around 1/3 from the boost face to the bore CL.

Interesting. So the trend is still to aim the A port front wall steeper, like also Jan said sometimes.
And doing so i imagine it becomes not profitable to make the B port front wall intersect CL at the same point (as i thought was some sort of a standard), as combining this with the hook of the rear wall will give too small of an effective cross area. Or am I missing something?
I guess they use something like the yellow line for the B front, right?

[Frits Overmars]

Interesting. So the trend is still to aim the A port front wall steeper, like also Jan said sometimes.
And doing so i imagine it becomes not profitable to make the B port front wall intersect CL at the same point (as i thought was some sort of a standard), as combining this with the hook of the rear wall will give too small of an effective cross area. Or am I missing something?
I guess they use something like the yellow line for the B front, right?Here you go Gradella.
354169

[Gradella23]

Here you go Gradella.
354169

exactly what i was thinking of, Frits. I used plenty of your concepts on my 50cc cylinder, so thanks!

[wobbly]

I made the front and rear walls of the A port cross the centerline at the same point in the 4DP - but this was just improving on " old " scavenging in the 90's from Yamaha.
They then got a Czech anemometric flow visualizing CNC machine and it all changed in 2000 when they went 5 port + T port , and the same scavenging regime as the Aprilia.
That is all but the B port front wall coincide on the center line @ 18% of bore - as Frits diagram shows.
Suddenly Yamaha had swallowed corporate pride , built a RS250 cylinder with Aprilia scavenging - except they kept normal stagger , and absolutely smashed the 250 class by taking 1st and 2nd with ease.

The idea behind all this is the flow column from each port may connect to the same radial coincident point on the bore CL but they are all separated axially.
In this scavenging regime the A port is entering Frits's " Pisa Tower " in the middle , the B ports are colliding with each other underneath that , and the C port is at the highest point , angled well upward
and pulling the column toward the wall above the boost port ( a sort of stratified charge process as used in direct injection technology ).
Thus the rising loop column " leans " away from the Exhaust port , reducing short circuiting , and making it U bend completely across the combustion chamber , increasing the scavenging of Exhaust residuals.

Nowadays the only variable to consider is what scavenging regime to use , reverse stagger or normal , and that is determined by the presence of a PV , or not.
Plus with no PV we need even more bias toward front side power and this entails the exact reverse of what all the old SOTA said was needed , slightly less rearward port radial angle.

EDIT - the 4DP made max power @ 12450 , the PJ switched @ 12650 and it rev'd easily to 13500. I tried the pipe a little shorter but there was less power under the curve - so much for Yamaha being so obsessed with
the short stroke to allow higher revs, it didnt.

[41juergen]

Got it Wob, thanks! One other question, have you merged the B and the C port to one?
RE the RS250 bridged exhaust port: there is a rumor that this was the idea from Guy Coulon at that time (copping the 500ccm design) as the TZ production racer had a triple exduct design..and the last version (TZ250 5KE4) had/has additionally a resonance chamber (as the Honda ATAC system) .minimizing the power dip between 7000 and 8000 rpm.

[a.montani]

Looking at the picture I noticed a knocking sensor. I am interested to detect knocking on a kart engine.
On the net I found Bylund automotive knocking shield. This shiel is using Arduino uno board.
below the link. do you have experience on this equipment?
what is the system (electronic) used to manage the knocking sensor in the picture on KZ cylinder head?
Thanks in advance for your help.

https://www.bylund-automotive.com/store/#!/products/knock-shield-2-for-arduino

[wobbly]

I have used for years the Czech made deto amplifier that outputs a 0-5V logger signal available on Ebay.
It can also have a ground wire added to interface with an Ignitech unit to retard the ignition when deto is seen.
Cheap , reliable and uses a standard Bosch sensor with 8mm thru hole available new or from car wreakers from BMW/VW/Benz etc.

https://www.ebay.com/itm/185739104413?hash=item2b3ee9d09d:g:wmYAAOSw7aBVBEo m&amdata=enc%3AAQAIAAAAwEyfISYVPMhGl3lBxtCyqLLiKHOaa MjJDSGSfbNmXHYbTKRl3y5hb5sK2PW0PCfztv8IwK5lS0peaqm 6MJzeeYeaKNlNOT3V0UFolkX0O8HsUX1qYNEtSgfGhTcTMN10y dum%2F5ZS%2BQMTIjDgIZiTyz4yTkwLd8t%2BKIE5dlbAeEmbW 12gd%2FRytiOWgzixGZOfLaA7zsFBJPeoAaWLhR%2F2z3qqC2b FA7yG1VbiFkznSZjje1Gnq6VLSOKqWcdai6AxjQ%3D%3D%7Ctk p%3ABk9SR47GtdigYg

[Peter1962]

Got it Wob, thanks! One other question, have you merged the B and the C port to one?
RE the RS250 bridged exhaust port: there is a rumor that this was the idea from Guy Coulon at that time (copping the 500ccm design) as the TZ production racer had a triple exduct design..and the last version (TZ250 5KE4) had/has additionally a resonance chamber (as the Honda ATAC system) .minimizing the power dip between 7000 and 8000 rpm.

I am not sure if it was over here, or on the pit-lane.biz forum but one of our most esteemed members already pointed out that the 'sudden' change by yamaha was seriously inspired by an illegal copy of a honda cylinder made by a mechanic with less than loyalty to his employer.

[wobbly]

Yamaha had seen the results gained by Harold Bartol who made his own version of a Honda style cylinder using the Czech made CNC anemometric flow visualization machine.
He was running Yamaha's 125GP program that was embarrassingly slow , but even though his cylinder was designed to fit directly onto the Yamaha case he was not allowed to use his stuff on the factory bike.
He showed me the dyno sheets of his cylinder against Yamaha's best in the pits at Philip Island , and he was far , far advanced over what they were capable of.

I had a plastic 3D printed cylinder for the BSL500 made and sent it to him for analysis , and it came back with alot of epoxy and grinding done.
Those changes were immediately incorporated into the models for the first 3D laser sintered alloy cylinders ever manufactured.
All the lessons learned by Bartol later ended up on the KTM250GP parralel twin , and Yamaha finally saw the light and ended up with pretty much what Bartol had developed.

[SwePatrick]

Part one(forced) dynosession of me and my friends Piaggio Roost twin.

To obvious reasons in this video it needed to be a two part video ;)


https://youtu.be/SV09p7ozq6Y?si=Fc6qJNTkk9J-wk09

[Gradella23]

Yamaha had seen the results gained by Harold Bartol who made his own version of a Honda style cylinder using the Czech made CNC anemometric flow visualization machine.
He was running Yamaha's 125GP program that was embarrassingly slow , but even though his cylinder was designed to fit directly onto the Yamaha case he was not allowed to use his stuff on the factory bike.
He showed me the dyno sheets of his cylinder against Yamaha's best in the pits at Philip Island , and he was far , far advanced over what they were capable of.

I had a plastic 3D printed cylinder for the BSL500 made and sent it to him for analysis , and it came back with alot of epoxy and grinding done.
Those changes were immediately incorporated into the models for the first 3D laser sintered alloy cylinders ever manufactured.
All the lessons learned by Bartol later ended up on the KTM250GP parralel twin , and Yamaha finally saw the light and ended up with pretty much what Bartol had developed.
Are there any KTM 250frr cylinder and engine pics around the web? Never seen anything but the assembled engine

[wobbly]

I have never seen anything but the one side on shot I posted.

[jamathi]

Yamaha had seen the results gained by Harold Bartol who made his own version of a Honda style cylinder using the Czech made CNC anemometric flow visualization machine.
He was running Yamaha's 125GP program that was embarrassingly slow , but even though his cylinder was designed to fit directly onto the Yamaha case he was not allowed to use his stuff on the factory bike.
He showed me the dyno sheets of his cylinder against Yamaha's best in the pits at Philip Island , and he was far , far advanced over what they were capable of.

I had a plastic 3D printed cylinder for the BSL500 made and sent it to him for analysis , and it came back with alot of epoxy and grinding done.
Those changes were immediately incorporated into the models for the first 3D laser sintered alloy cylinders ever manufactured.
All the lessons learned by Bartol later ended up on the KTM250GP parralel twin , and Yamaha finally saw the light and ended up with pretty much what Bartol had developed.

bartol did nothing else than always copy the latest Honda cylinder he could lay his hands on
As I saw when working for Derbi.
The Best cylinder gave 47.5HP
We had such a Czech flowbench at Aprilia
It proved totally useless, and was soon eliminated...
By the way: how many World Championships did bartol win against mine 49?

[jamathi]

Are there any KTM 250frr cylinder and engine pics around the web? Never seen anything but the assembled engine
https://media.nationthailand.com/uploads/images/md/2023/12/gnhY6iwiHCsJnXSlnsZW.webpy
You can be pretty sure it was honda copy.....

[husaberg]

Are there any KTM 250frr cylinder and engine pics around the web? Never seen anything but the assembled engine
https://www.kiwibiker.co.nz/forums/album.php?albumid=4901
https://www.kiwibiker.co.nz/forums/album.php?albumid=4857

https://media.nationthailand.com/uploads/images/md/2023/12/gnhY6iwiHCsJnXSlnsZW.webpy
You can be pretty sure it was honda copy.....

Was the reed derbi also a copy of the Honda Kit?
Only reason i ask is the pipe is the same?

[wobbly]

You are right Jan , even the pipe used on the KTM was pretty much an A kit Honda copy.
Although I did very much like the design concept of the KTM being a parralel twin , running at 90* firing with a balance shaft.
This gave symmetrical intake and Exhausts , not possible on a V configuration.

[jamathi]

https://www.kiwibiker.co.nz/forums/album.php?albumid=4901
https://www.kiwibiker.co.nz/forums/album.php?albumid=4857


Was the reed derbi also a copy of the Honda Kit?
Only reason i ask is the pipe is the same?

Yes, of course it was....

[JanBros]

KTM 125 http://www.pit-lane.biz/t118-gp125-caracteristiques-ktm-frr
KTM 250 http://www.pit-lane.biz/t606-gp250-ktm-250

but you have to be registered to view pictures

[Frits Overmars]

Yamaha had seen the results gained by Harold Bartol who made his own version of a Honda style cylinder.. . He was running Yamaha's 125GP program that was embarrassingly slow , but even though his cylinder was designed to fit directly onto the Yamaha case he was not allowed to use his stuff on the factory bike.You bet Yamaha saw the results. They had paid the development of a better cylinder and they were less than pleased when the end product turned out to be a shameless Honda copy. Can you imagine how that must have hurt in the traditional Japanese culture? No wonder they prefered to struggle on with what they had rather than have those cylinders on their works bikes.


bartol did nothing else than always copy the latest Honda cylinder he could lay his hands on as I saw when working for Derbi.Jan could have added that a son of our mutual friend Cees van Dongen used to race a Yamaha TZ125. In order to cure its mediocre power, Cees equiped the little Yamaha with a Honda RS125 cylinder. That gave Bartol an idea....

After Bartol left Derbi for KTM, taking with him the Derbi 125cc faring mold, developed by Porsche and paid for by Derbi, we noticed a couple of things.
Team mechanics may stay friends, even after they went to work for other teams, so we happened to have the drawings of the latest Honda pipes :msn-wink:.
And below is the exhaust of the works KTM 125. And of course we had the Derbi works drawings.
Carbon copies, the three of them.
354180

[a.montani]

I have used for years the Czech made deto amplifier that outputs a 0-5V logger signal available on Ebay.
It can also have a ground wire added to interface with an Ignitech unit to retard the ignition when deto is seen.
Cheap , reliable and uses a standard Bosch sensor with 8mm thru hole available new or from car wreakers from BMW/VW/Benz etc.

https://www.ebay.com/itm/185739104413?hash=item2b3ee9d09d:g:wmYAAOSw7aBVBEo m&amdata=enc%3AAQAIAAAAwEyfISYVPMhGl3lBxtCyqLLiKHOaa MjJDSGSfbNmXHYbTKRl3y5hb5sK2PW0PCfztv8IwK5lS0peaqm 6MJzeeYeaKNlNOT3V0UFolkX0O8HsUX1qYNEtSgfGhTcTMN10y dum%2F5ZS%2BQMTIjDgIZiTyz4yTkwLd8t%2BKIE5dlbAeEmbW 12gd%2FRytiOWgzixGZOfLaA7zsFBJPeoAaWLhR%2F2z3qqC2b FA7yG1VbiFkznSZjje1Gnq6VLSOKqWcdai6AxjQ%3D%3D%7Ctk p%3ABk9SR47GtdigYg

Thank you for your suggestion.
My target is to use it on track keeping under control knocking ang exh temperature during tests.
once I know right exh temperature "close" knocking (but in safe area) I could remove the sensor during race.

What do you think'

I will keep you updated.

thanks Again and happy NEW YEAR TO EVERYBODY FROM ITALY!!!!!!!!!!

[katinas]

KTM 125 http://www.pit-lane.biz/t118-gp125-caracteristiques-ktm-frr
KTM 250 http://www.pit-lane.biz/t606-gp250-ktm-250

but you have to be registered to view pictures

A few pictures that where posted here. Looks like piston edge was slightly rounded .

[crbbt]

You bet Yamaha saw the results. They had paid the development of a better cylinder and they were less than pleased when the end product turned out to be a shameless Honda copy. Can you imagine how that must have hurt in the traditional Japanese culture? No wonder they prefered to struggle on with what they had rather than have those cylinders on their works bikes.

Jan could have added that a son of our mutual friend Cees van Dongen used to race a Yamaha TZ125. In order to cure its mediocre power, Cees equiped the little Yamaha with a Honda RS125 cylinder. That gave Bartol an idea....

After Bartol left Derbi for KTM, taking with him the Derbi 125cc faring mold, developed by Porsche and paid for by Derbi, we noticed a couple of things.
Team mechanics may stay friends, even after they went to work for other teams, so we happened to have the drawings of the latest Honda pipes :msn-wink:.
And below is the exhaust of the works KTM 125. And of course we had the Derbi works drawings.
Carbon copies, the three of them.
354180

But the exits out of the right side of the bike. 100% different now :laugh:

---------------------------------------------------------------------------

I have read two separate articles saying the Aprilia 250's had traction control in 2009.

All I have discovered is that the traction control was achieved by monitoring the acceleration rate of the RPM increase of the engine. Then potentially pulling ignition timing (which would dump heat/energy into the exhaust, "shorten" the pipe)

I am wondering if the lean angle was also used as a parameter?
and I am guessing there are situations where advancing the timing would be the way to limit the RPM spike.

I guess what I am after is how the traction control actually worked on the 250's

[Haufen]

https://www.kiwibiker.co.nz/forums/album.php?albumid=4901
https://www.kiwibiker.co.nz/forums/album.php?albumid=4857


Thanks. Btw, the first link says
Invalid Album specified. If you followed a valid link, please notify the administrator


What is the reason behind the dual angle kinked negative squish area? Did KTM have pistons with a corresponding shape, or a bowl, too?

354188

[husaberg]

Thanks. Btw, the first link says


should work now.

[Frank S.]

Was there detonation at the outer "ring" ?
Also the piston looks like sandblastet in that area.