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      11-11-2012, 03:48 PM   #144
Twin Turbo User

Drives: 2009 G8 GT TT -> 08 E90
Join Date: Jul 2011
Location: STL

iTrader: (1)


Originally Posted by Tiago@VRSF View Post
If you're in 5th or 6th going 40mph, any exhaust will drone
There's a fix for that, and only requires a short length of capped off pipe.'s called a Helmholtz pipe.


Here: (where I learned about it with my old G8)

The theory:

There's a formula for figuring out the particular length required for a particular drone frequency. Simply put, it's:

1100 feet per second (the speed of sound)
divided by the drone frequency.
Divide this result by 4 to give a quarter wavelength.
Multiply the quarter wavelength number by 12 to give the required chamber length.

These chambers are pipes cut and welded into the tailpipes and capped off on the other end, creating a closed "echo chamber" to reflect back the drone frequency 180 degrees out-of-phase, thus cancelling it out.

It works. Try it and enjoy your exhaust.
No charge for this info... unless you want to use me as a guinea pig for the new design, then I'll take a set and do lots of testing
New: 08 E90
Old: 09 G8 GT Twin Turbo'd by ME: 11.6 @ 125