Just get a name brand muffler or even if you don't care, get a generic high-quality muffler and get the pipes done custom at any muffler shop. If you decide to keep the stock size piping, then it should be nice and quiet.

I saw a WS6 on the road the other day. I really like those cars. It's very original compared to the other domestics, but on this one it said "import killer" on the back. I was pretty offended by this because I know that most imports have little chance against it, but you can't say that you can beat them all. I dunno, but if I had a quicker import (NSX, Supra, M3) I'd key that car up...actually, I hate haters so I wouldn't do it, but I'd have a problem with it and have a talk with the owner...after beating his ass in a race.

No offense to domestic owners like you though. I think they're great for drag/racing. Just don't get cocky about it.