every brand on the market tells you a ridiculous increase of HP by only changing the pipe and that's falseyou will get that HP when you combine with others exhaust components like headers and pipe.ill make you easy, the only difference between stock muffler and performance are the noise retention, that's itstock muffler has a lot of something like cotton inside that will take the noise away instead of the racing one who has only a bit of "cotton" or don't have anything for best results replace the whole exhaust system with a racing one