I agree with SamPap. I ran straight exhaust (no muffler, no cat) for about a month and it had nice sound under full throttle, but was raspy and had an irritating high pitched sound to it (not the turbo). I put on a 4" straight through glasspack (Dynamax I think) and that took all the high pitch noise out of it, and it sounds great now, with no increase in backpressure compared with open exhaust.