Despite what car "enthusiasts" think exhausts are tuned for sound which isn't necessary to make more horsepower...it's simply something that car guys want. Obviously there's a point where that stops becoming true or at least the effects are too minimal to make a difference. Some of the most efficient exhausts for street cars are among the quietest. If noise restrictions are put in place for new cars companies like Ford will simply quiet the cars down and in the end they'll be just as fast.I had the pleasure of hearing the new BOSS mustang's custom exhaust, and while idle I have to say impressive the thing didn't get too loud at full throttle, loud but not as loud as I expected.
I wonder how this ordenance will effect the new muscle cars coming out.