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      10-31-2012, 07:26 PM   #14
Gjm127's Avatar

Drives: BMW 435i xDrive M-Sport
Join Date: Nov 2011
Location: Montreal, QC

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Originally Posted by S65B40V8 View Post
Sounds like a great engineering project. Hopefully you have access to an M3 for measurements and photos? If not, contact your local BMW club or service shop and ask around. Since you are specifically targeting the M3, it would be best if you could design something that sort of looks like it would actually fit on the car.
Why a "full race exhaust"? The best race exhaust is probably just straight pipes -- pretty boring project Why not set your design as a "flow and sound optimized street exhaust"? You could first model the factory exhaust and then compare flow (sound is more difficult) to your own design. The factory muffler has 2 roughly 90 bends for each pipe inside. It is claimed that these restrict flow. Do they? How much?
What CAD system do you use? Solidworks for instance has a nice flow modeling package that would be very useful for this but for your project, maybe it's better to calculate what you can on your own.
It seems that most street exhausts for the M3 that don't drone (unpleasant resonating noise heard in the cabin) in the 2k-3k RPM range use Helmholtz resonators -- that right there is a great engineering design exercise for your project (examples include: AA, Dinan, Corsa). Some good info. to get you thinking (click on the M3 exhaust link):
You can also search the posts here and other sites for some good discussion on Helmholtz resonators in exhaust systems.
Good luck!
I am so thankful for all the information I'm getting from you guys. You're helping me make a very fun project out of it!

That Helmholtz box is very interesting, I would love to integrate that into my project. You are right, the best "race" exhaust would be straight-piping the whole thing heh, I could write a one pager and that would be the end of it haha. You're right though, I'm gonna look into resonators to eliminate the drone, etc... I think it gets rid of unwanted pops as well...

I use Catia V5 (from Dasseault Systemes) as my CAD system, it's very much like Solidworks (actually brought by Dasseault Systemes as well). It's gonna help me calculate lots of things.

I am amazed by the amount of information Dinan has released to the public too. That website is gonna help me a lot too.

All in all, big thanks to all you guys!