| Subject: |
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Re: exhaust |
| Name: |
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Paul Vanderheijden |
| Date Posted: |
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Apr 8, 08 - 9:36 PM |
| Email: |
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paul@scuderiatopolino.com |
| Website: |
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http://www.scuderiatopolino.com |
| Skype Address |
|
pheyden |
| Message: |
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Hello Florian,
Sorry it has taken a few days to get back to you.
Exhaust systems are ALWAYS built with a particular outcome in mind. The length and diameter of the primary tubes, the ones that connect to the flange on the side of the head, are are chosen based on two factors, the displacement and RPM range where the system is to be effective. The collector is the second part of the system and can be used to fine tune the overall performance.
So, the primary diameter is principally determined by the displacement of the cylinder, and the primary length determined by what RPM the system is to work best. There are some other "basic" rules. A larger diameter tube, slightly shorter in length will work well at higher RPM. A smaller diameter primary will work better at lower RPM. That is why an FI engine uses very big diameter primaries, that are very short and have a very short collector that is slightly larger than the primary tube itself. After all they are trying to get it to be resonant at between 17,000-19,000 RPM.
It is pretty difficult to get any exhaust system to be efficient at more than a 2-3000 RPM band. Systems that are a tri-Y design have a slightly broader torque band than 4:1 systems.
I won't get into what the optimum exhaust air speed should be, as this is probably going too deep. I recently modeled a new exhaust for an 1168cc A112 motor with a top RPM of 8500. This came out with 30mm primaries 650mm long, and a 50mm collector only 300mm long. This was in conjunction with a PBS 8 port cylinder head. I would not be afraid of small primary diameter exhaust systems, as they will work quite OK for most applications.
Hope this helps. |
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