I have been building turbo Buicks for many many years. One car I helped build the majority of the power train/fuel system/etc. Had a single turbo StageII with a 3.5" downpipe. He also had a three muffler 3"system on it and you could hear the Weldon fuel pump over the exhaust sound. Car owner HATED the dreaded Buick Turbo 2200rpm drone! Well, after a few years running 9.1's @148, myself and another local smart guy talked him into a Dyno session with a cut-out installed in the down pipe. Ran it first all capped up and running through three Dyno Max Ultra Flo's (the third muffler behind the rear end, was a custom made cross-flow muffler in 3"). Then we ran it with the cut-out open and that sum bitch picked up an amazing SIX FUCKIN HORSEPOWER!!!
What was amazing to us "smart" guys was that it would have ran NO faster. (Maybe .05 if he removed 50 lbs. of exhaust weight. Who knows.
His Street car (same guy) runs 9.9's @136 through a similar 3 muffler system but in 2.5". I can't hear him drive up my long driveway. Idles smooth as glass, too.
LOUD does not mean fast!