ESE's works engine tuner

[aljaxon]

all sounds good wobbly. if i go for a single stage diffuser am i losing out too much? i tried getting my head around blairs multi stage diffusers but to the "power e" mashed my brain. ive searched for a rule of thumb to set multi cone angles percentages. the closest i found was using 2t calc software and borrowing the dims. sort of.

the bike has a gilardoni 74cc reed kit fitted. so not too ancient but nothing like the optimum.

[F5 Dave]

Google. . Oh, a Puch. We never got those.

[Frits Overmars]

i want to make a pipe using FOS...

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.

when designing a pipe im thinking that the suction wave travels slightly faster than the stuffing wave due to it passing through hotter parts of the pipe. so should i take the time to work this out?

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.

[aljaxon]

frits it wasnt that the answers didnt suit me, it was the cylinders architecture that couldnt be changed. you were very helpful in telling me what i couldnt do in this regard but didnt tell me what i could do. i still dont know. there were only you and janbros offering me advice. janbros suggested tapering back towards the FOS dimensions. i would have loved to have heard something similar from you. or another solution. even if it was less than ideal.

that was on a mobylette with an 82cc parmakit. i tried doing a copy of that motor with the timings you suggested but (still havent a clue as to the pipes start dimensions ) now need some way of getting it past the lack of power at mid range. and with it being a single gear it means fitting a high bite clutch. so i shelved that project. the original project with the flawed durations revs to 12000 and produces peak power at 9k rpm and ive left it alone. . 65mph for a mobylette is fantastic


this is a new project. its a Puch M50 sports. 4 gears. 74cc cylinder. different stroke and porting. 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? i wont be developing anything i havent a clue. i will just be going for best case scenario.

with me being a humble thick bricklayer i think at times frits you lost your patience with me.

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? because the reasons might be the same ones that prevent blairs calcs from working. because thats my back up if im not using the FOS.

together of course with wobblys suggested percentages.

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?

[aljaxon]

Google. . Oh, a Puch. We never got those.

No puchs at all in NZ?
in the uk 16 yr olds were limited to below 50cc and puch were one of the first to have gears. ( later called sports mopeds.) M50 sports were slow 40mph and heavy 85kg, yamaha fs1e's -fizzies and the later puch grand prix were 10 kg lighter. and 5 to 10 mph quicker. mine did as many miles being pushed. in fact thats how ive heard some people say puch as in push or poosh.

[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.

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!Atyzb5b7jtWNmVcX...5eKjL?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!Atyzb5b7jtWNmVcX...5eKjL?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 , 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.