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Exhausts Exhausts - Headers, Mid Pipes, Mufflers


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November 15th, 2017, 11:10 AM   #1
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Exhaust design?

628cc
If you were to design an exhaust system from scratch, ideally where would you join the twin header pipes to the collector? How would power and torque change if the join was made close to the head or a long distance away?
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November 15th, 2017, 11:55 AM   #2
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Best person to ask would be the dohc guy ...I read a few thread months ago about it on the Internet there is a lot to talk and also size is involve ...myself personally I would be also adding powerbomb to the list an exhaust with no reversion should be a good one (still diameter and lenght is involve) ....i have thought to have a system similar to aprilia sxv (not now but next year maybe) just love that bike

I am pretty sure akrapovic have the collector with a different lenght, standard one is different (worth looking into that ) or what other manufacturers went
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November 16th, 2017, 12:35 AM   #3
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Hey Canolman,
I've been looking at making headers for my Flat tracker to bring the pipe down the right hand side. There are so many different calculations, options (things to get wrong) I'm going to try and copy the factory dimensions as closely as possible. I reckon those Swedes did a pretty good job.

Carl.
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November 16th, 2017, 05:40 AM   #4
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Thanks Carl, I'm looking at a few ideas, one being twin outlets down the front of the motor and joining about half way under, just wondering if that is a bit long?
Its all about space on this build, something I have very little of!
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November 16th, 2017, 09:32 AM   #5
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The standard length of header would be close to reaching under the engine, you may need the join just before.
DrC or Bushie must be the guys in the know for this.
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November 16th, 2017, 09:54 AM   #6
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Calo do you live in south Wales? If you need some measurements on mine dual exhaust(sr one) next spring I will be around the area I can show you it ...but mine goes where the starter motor is, shock is a problem as the reservior is the way but I cold help you out with that as I might not need it
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November 16th, 2017, 11:15 AM   #7
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Its really difficult to say whats best, normally empirical testing is the cheapest. There are a few softys out there like maxpipe and vannik, if you have the time and patience to put the numbers in with accuracy.

I had the opportunity to try out an mx bike in the dyno with a good customer, I told him to bring an exhaust that you can change the length on and well have a go, and so we did and the longer it got the better results all over the range, we even had it protuding the rear fender.
We directly went back to the reference length and it was spot on power with that, so no illusion (no change of test environment that is).

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November 16th, 2017, 11:47 AM   #8
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Many thanks to you all. What I'm trying to determine is what effect using long twin outlets would have on power and torque? On our possible redesign making the join under the engine solves so many problems. No space in front of the engine because of the radiator and suspension travel, no room either side because of the bodywork! Overall length is easy to play around with on a track bike.
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November 16th, 2017, 12:00 PM   #9
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I dont think any, summed area and their length is it in my opinion.
Pretty much all manufacturers did separate pipes at this time, fashion maybe?
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November 16th, 2017, 01:05 PM   #10
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Originally Posted by canolman View Post
628cc
If you were to design an exhaust system from scratch, ideally where would you join the twin header pipes to the collector? How would power and torque change if the join was made close to the head or a long distance away?
Many thanks
Well, the fun thing with exhaust design is that it is still involving some "black magic", whereas most other things in combustion engineering have well developed theoretical models.

All other aspects aside, the wizards are stating that the effect you want from the reflected wave will be stronger if kept together. Meaning that joining the pipes as early as possible after the ports, is beneficial. It will not change the characteristics, but make the effect stronger and possibly more focused in the rpm band. Keeping the flow in just one pipe will reduce the media to wall pressure loss, also pointing in the direction of keeping the exhausts in one single pipe for as much of the distance as possible.

Now the Husaberg exhaust ports are pointing in different directions, making it less optimal to join the primaries swiftly, out of pure pressure drop reasons... The best thing would have been to join the ports already in the cylinder head. But then there is sometimes no room for a thick primary tube between the engine and the front wheel or water cooler...

I do not think that the location of the joint (!) will play a key role in the characteristic. At least not compared to the length and diameters of your whole system!
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