I have an off road X-pipe and a SLP loud mouth... which was so damn loud I had to take the crap SLP gave me and put the only thing I could find to fit in its place.. which was some 4 inch Magnaflow race mufflers... and it is still pretty damn loud... too loud really, its louder than my heads, cam, supercharged 90 GT with 3 inch dumps that I had... its not so bad when your all the way on it, or at idle... but when your just pullin out normal at about 2,500 rpms it throws out this horrific redneck blast!! The up side is the quality of the cat back was great, better than my brother's Bassani thats on his Cobra, which sounds great.. and the tips that SLP gives you look awesome, especially since I shine mine with steel wool... it also must be good for power... I haven't dynoed my car, but I do know that 11.6's at 122 in Louisiana summer time heat is cookin with the few mods I got... hope that helps, Travis.