sorry didn't look more into the thread at this moment, but just thought to add if your getting an inspection on your car and you know about it shove steel wool down your exhaust it takes the loudness down and everything. a trick alot of people do on cars and bikes to pass through these type of things.
have not personally tried it myself. but have been told that it does work.
feedback is appreciated. if you have tried it or do try it out.