This is a 2.5" mandrel bent cat back that sounds great with the x-pipe(catted or off-road) or stock converter(catted) h-pipe. A huge decrease in back pressure. Magnaflow stainless steel converter pipe back kit will increase horsepower and torque. On an 04' Cobra with the off-road MagnaFlow x-pipe the car gained 58hp/61lb-ft at the rear wheels. Free Reg Ground UPS shipping on this item