Just wanted to post my experience driving my S4 Avant with my newly installed JHM piggies. From my butt dyno, I can't believe how much pull my car now has! Even on 6th gear and doing above 80mph on the freeway, it feels there's more power left from the engine. The sound coming from my cat-back has a heavier (much deeper) bass than before. It actually gives a little rumble now and then. FYI, from my experience and some videos I've seen APR cat-backs don't really do rumble. Hehehe...so happy!!!