I have a 3" downpipe with cat and stock catback with the mufflers replaced with flowmaster 40 series. I'm not sure where people get that these things sound like ass with them because I love the way it sounds. Yes it does drone a little but nothing that you wouldn't expect with replacing the mufflers for performance ones. I have the stock resonator but I wanted to change that out for something as well. Maybe a glass pack or maybe some whisper resonator from ZZP.