The choice of a manifold is depending the track and gearing. In the past Mugen came with 17/20 and with the MRX5 and later the gearing has changed to 16/20 while a lot of drivers even like to run 15/20. Then yes, a short manifold could be the better choice but it does not take away the standard theory about the length of the exhaust system and where in the rpm range the best power is.

it was not a book it was an online site I read it 15 years ago the first time I ever had a nitro car in my life,,, what sight I have no idea from that long ago search around maybe u can find it,,,,

Yes, that is one scenario, the gearing could be off.


As it's not any extreme differences in manifolds in onroad, the end scenarios isn't likely to happen, they should all work without any Big problems.

There are things that happens besides the high pressure puls that people tune for, but it's of far less importance. Everything can and is being calculated pretty good these days, or at least it can be done.

Still like to see what 's written in that book though, to see how they are thinking.

lol...fool

Okay, I don't think I can find it. I have read all the stuff that people usually read when it comes to two strokes, drawn conclusions that isn't there. I have read what people don't usually read regarding two strokes, I have read even more on four strokes, drawing more conclusions. (One of them are that you really don't know everything, no one does, but the basics isn't wrong)
I believe I would have remembered it, but I could be wrong.

again was not a book and didn't really explain was one sentence said using a shorter manifold allows for the pulse wave to return faster allowing the motor to get on the pipe faster that was really it. it just always stuck in my head that way and I use it that way don't think I done to bad over the years.

I love the way u guys went from I'm a retard to oh maybe with different gearing and bla bla bla lol don't be so quick to judge nothing is ever set in stone because novarossi says use it ??? lol

Nah, I’m still on the hogwash bandwagon. Long manifold = lower rpm peak power; short manifold = higher peak rpm power. However if the engine isn’t timed for the manifold being used, the engine will tell you by not running correctly. An engine will stage on the pipe at a lower rpm on a long pipe/system.

Many times, the “I read it in the internet” line goes into the trash bin of acceptability. Especially in this case.

internet line goes goes in the trash!! y I said go out and test for yourself!! its funny all u guys disagree and not one person has said I have tested it on the lap counter ? do u guys practice with a lap counter? or u just go out and say ok long manifold I'm slow and short I'm still slow lol!! geez I love people that talk theory, except roeolf I'm confident he has tested pretty much everything on earth.. but really u guys mean to tell me all your years of racing u just accepted long mean top end !! lol

another thing you keep saying which is totally wrong u keep saying long manifold lower peak power !! dude no manifold increases or decreases peak power period!! get that out of your head only roll of a manifold is to speed up of delay the time it takes for the pulse wave to send back the unused portion of the fuel called scavenging and reach peak power, but u will always hit peak power no matter which one your using.. I'm talking about when u have a pipe and manifold set on just changing the length does not loose or gain power, if u said I had a 2015 set on and I changed to a 2069 then that's different one set up can give u less power but not just changing the length.

so roeolf explain the logic that if the pulse wave is sent out and on return forces the unspent fuel back in and causes the extra charge right, so what logic is it that if a longer manifold is used and takes the pulse wave longer to return that it would make sense that the power comes on faster? as apposed to a short manifold sending the pulse wave out and returning faster causing the power to ignite quicker? maybe my brain works backwards ...

Quite possible.

And I'll pass u backwards

You need to be over 21 to purchase a long manifold.....LOL

All the pipe length does is move the powerband up or down the rpm range. It does not effect the maximum power much- assuming the pipes/manifolds are a good match for the port timing.

I'm going to be honest and tell you that the reason why I haven't tested with lap counter, it is that I'm not racing competitive and usually run offroad when I'm at a track. I'm in this hobby pretty much only for the technical part, to develop things, it was the same when I raced full scale. But with that being said, I'm therefor interested in how we have a different opinion in this matter, what's missing to understand each other. :)

As a complete package: engine, manifold, pipe, clutch, gearing etc etc, I couldn't tell you what's fastest for everyone every time.
But as far as the engine alone, how that respond, I do know pretty well what happens.
I have read a substantial amount of technical papers, talked to people or read what they have tested in many places on this earth. There is no question about what happens when you change the manifold length in regards to where the power peaks appear.
But that's just the engine, and further, it doesn't tell you what happens to things like over all power and width of the power band. Part of that is that the length isn't a design parameter.

For instance, if you increase the rpm where the peak power occurs, it is likely that the power increases due to the fact that hp is a function of torque/rpm. But if you're out of the range where the engine likes it, the peak torque might go down or even the rpm spread between the two might get more narrow, so you'll end up with less Over All power even if peak power has increased slightly.

Further, the engine will not ignite the mixture any earlier only because the puls is returning any faster, the piston moves according to rpm, and the puls according to temperature. So in a fixed scenario with the temperature, the piston will be further up when the high pressure puls returns at high rpm and further down at lower rpm.
If it's too early it will push the mixture back down the transfers (which happens at low rpm), or if it's to late the puls wont have time to push in what ever fuel mixture there is in the manifold (which happens at high rpm).
But, that is only the high pressure (positiv) puls, the low pressure puls (negative) will also have an impact on how it turns out. A bad scenario at the bottom end could possibly be tuned out by the clutch for instance.

So I don't question that your lap times are better, I'm just not sure why.

First of al we are talking about where the power is with the used manifold, not what effect the manifold has on the laptimes.

The wave of the resonance will act as a wall at the exhaust port when the mixture does reach the exhaust port at the same time, they collaps each other. When it is exactly on time it is at the opening of the exhaust port, no fresh fuel will pass through and no dirty gasses will enter the engine leaving the maximum fresh fuel to combust.
The faster the engine spins the faster the fresh fuel will be pumpd up from the lower crankcase and also is pumped faster into the cilinder. So on high revs the fresh mixture will reach the exhaust port much faster than at lower revs. So on high revs the wave has to be quicker at the exhaust port than at lower RPM for the ideal situation.

no see this not what said in the other post u said u get less rpm depending on the manifold and that's wrong now u saying changing the manifold will dictate where u get peak rpm now that's right!!! what I was saying to u is rpm wil be rpm with any manifold/pipe combo no matter long or short. another words u will always hit 40k IM JUST USING A NUMBER but if this pipe/manifold combo gives u 40k rpm then u will always hot 40k weather long or short just when it will hit 40k is the difference. I don't know if u ment to say that in the other post but it can out as if u go to a short manifold u will not hit the 40k... all I'm saying:):):):)