The only bolt on mod that I have done is put on a magnaflow catback 15868 for 04's and I can really say that it is louder than stock w/ no drone and definately puts more pep in the step. The best $526.90 I've spent yet. Also the installation was a breeze. Now keep in mind that my wife wants to drive my car occassionally so the Flowmaster super 40 series was out of the question. All I know is it gets really loud when I get on it and it is getting louder as it burns in and it's only been on for @ 1 week.