k, someone please tell me why all the aftermarket exhaust sytems for the 6i are 2.25? that is the stick size. now, correct me if im wrong but when u get cat-back exhaust you go a size up right? i know i did. i went custom, got a CAI, Magna-flow high flow cat, no resonator, and 2.5 all the way back, and magnaflow mufflers. im thinkin ive gained 10-15 whp? neways if you guys could answer as many of the questions as possible thatd b great. thx.