go down to the oil rigs and just go ahead and getcha' some 8 in drill caseing and get er done, ive heard a 01 with 6" straight back, sounded damn good, kinda brought a tear to my eye, performance might suffer though. 4-5 is as big as you really need, velocity gets slow when you break the 5 in mark and exhaust slows down a bit, unless your pushing alot of juice!!!!