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Restricted exhaust
Posted: Sun Dec 10, 2017 8:47 pm
by RCJ
If rules dictated a small primary pipe diameter and a restrictive muffler.Would you make the exhaust system as short as feasible.
Re: Restricted exhaust
Posted: Sun Dec 10, 2017 8:53 pm
by ptuomov
RCJ wrote: ↑Sun Dec 10, 2017 8:47 pm
If rules dictated a small primary pipe diameter and a restrictive muffler.Would you make the exhaust system as short as feasible.
I wouldn’t, assuming it’s a V8.
I would make the small diameter primaries very short but then pair 4-2-1 and Y pipe go much bigger for secondaries and all the other exhaust pipes. 4-2-1 allows you to avoid both 90 degree and 180 degree exhaust blowdown interference with very short primaries. What restrictions do you have on the length and style of the headers?
Then I’d run the muffler all the way at the rear bumper after exhaust gas has cooled and all the pulses have been combined. The key is to cool the exhaust with minimum restriction before the muffler, how about running aluminum exhaust pipes to maximize cooling?
Re: Restricted exhaust
Posted: Sun Dec 10, 2017 9:55 pm
by Curtis Mc
Is this a theoretical question or are there specific rules you can point to? You may get all sorts of ideas if people can see the rules as written.
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 8:11 am
by RCJ
This is for my grandson's racing kart.4 stroke single ,79cc.Exhaust port is .900 dia., pipe inside dia. .625.I've raised the pipe to the top of the port and made a thick flange that I can blend.Pipe is 8'' long with a 90 degree bend off the head, can get to 20'' with no more bends.Any longer and I would have to add bends.
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 9:35 am
by englertracing
What's the muffler?
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 9:41 am
by ptuomov
RCJ wrote: ↑Mon Dec 11, 2017 8:11 am
This is for my grandson's racing kart.4 stroke single ,79cc.Exhaust port is .900 dia., pipe inside dia. .625.I've raised the pipe to the top of the port and made a thick flange that I can blend.Pipe is 8'' long with a 90 degree bend off the head, can get to 20'' with no more bends.Any longer and I would have to add bends.
Does the entire pipe between the port and the muffler have to be .625" inside diameter? Or does only the first 8" have to be .625" ID?
Is there a restriction on how thick the flange can be?
How much CFM does the muffler flow and at what test pressure?
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 10:35 am
by RCJ
The pipe has to be .625 all the way to the muffler.Here is a link to the muffler.I can remove the internals from the muffler.
https://www.bmikarts.com/RLV-Mini-91-Mu ... _p_36.html
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 10:46 am
by ptuomov
Are you allowed to extend the pipe after the muffler?
What I'm thinking is gutting that silencer and making it effectively "a step" in the exhaust primary. Then extending at the appropriate size pipe from the silencer. One idea could be to set the length of the .625" primary such that when the blowdown wave hits the step, it reflects a low pressure wave back to the cylinder that is timed such that the exhaust valve seat is no longer close to sonic velocity. Then the longer bigger pipe downstream of the "silencer step" is timed to send back a low pressure wave around the overlap. If this would be legal, that is, putting a gutted silencer between the small primary and large "secondary", it might make some sense to model and/or test it.
Just throwing out ideas here, I've obviously never done anything like this.
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 12:40 pm
by Curtis Mc
Do the rules state you can't have two mufflers? Something like a "Y" at the end of the appropriate blow-down length?
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 3:20 pm
by Ron E
Is this a OHV engine, or a flathead?
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 4:43 pm
by RCJ
OHV.
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 5:24 pm
by pamotorman
RCJ wrote: ↑Mon Dec 11, 2017 8:11 am
This is for my grandson's racing kart.4 stroke single ,79cc.Exhaust port is .900 dia., pipe inside dia. .625.I've raised the pipe to the top of the port and made a thick flange that I can blend.Pipe is 8'' long with a 90 degree bend off the head, can get to 20'' with no more bends.Any longer and I would have to add bends.
the 90 degree bend would hurt the flow. if you want length form the pipe in a big radius
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 6:05 pm
by cjperformance
ptuomov wrote: ↑Mon Dec 11, 2017 10:46 am
Are you allowed to extend the pipe after the muffler?
What I'm thinking is gutting that silencer and making it effectively "a step" in the exhaust primary. Then extending at the appropriate size pipe from the silencer. One idea could be to set the length of the .625" primary such that when the blowdown wave hits the step, it reflects a low pressure wave back to the cylinder that is timed such that the exhaust valve seat is no longer close to sonic velocity. Then the longer bigger pipe downstream of the "silencer step" is timed to send back a low pressure wave around the overlap. If this would be legal, that is, putting a gutted silencer between the small primary and large "secondary", it might make some sense to model and/or test it.
Just throwing out ideas here, I've obviously never done anything like this.
I like that idea, whether its legal or not is another thing
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 6:07 pm
by ptuomov
cjperformance wrote: ↑Mon Dec 11, 2017 6:05 pm
ptuomov wrote: ↑Mon Dec 11, 2017 10:46 am
Are you allowed to extend the pipe after the muffler?
What I'm thinking is gutting that silencer and making it effectively "a step" in the exhaust primary. Then extending at the appropriate size pipe from the silencer. One idea could be to set the length of the .625" primary such that when the blowdown wave hits the step, it reflects a low pressure wave back to the cylinder that is timed such that the exhaust valve seat is no longer close to sonic velocity. Then the longer bigger pipe downstream of the "silencer step" is timed to send back a low pressure wave around the overlap. If this would be legal, that is, putting a gutted silencer between the small primary and large "secondary", it might make some sense to model and/or test it.
Just throwing out ideas here, I've obviously never done anything like this.
I like that idea, whether its legal or not is another thing
Everyone likes a barely legal idea, right? Me too!
Re: Restricted exhaust
Posted: Mon Dec 11, 2017 6:18 pm
by cjperformance
yep they are always the best ideas