Do you still have the stock catalytic on the car?
A good quality glasspack with large louvers inside will only restrict the flow a little but catch some of the raspy noise. 318's will still drone at lower RPM and on the highway. I've tried 4 different exhaust on my car including uninsulated resonators and mufflers that from my experience, sound very raspy and "throaty".
Try and fit the longest possible glasspack and muffler, even if you have to weld two 12" together or something along those lines. You wont lose any performance by giving the M42 a little back pressure and going with 2" pipe, high RMP power is all in the cam timing and chip tuning.
The major difference between my 318is and an e30 M3 is that the noises come from the engine and not the passengers
Last edited by Slowered318; 05-30-2013 at 09:52 AM.