Flowmaster should be taken to court for false advertising. Worst perf. muffler on the market. I use magnaflow race mufflers on my chevelle. 4" straight through stainless mufflers w/ x pipe. 540 w/ 15:1 comp. and haven't been bothered by the cops yet on the street. At the track it runs the same with or without exhaust. Pay a little more now and be happy for years to come!