As Mike has already said, mount the muffs as far back as you can, preferrably behind the rear end housing forget the Flow Masters, look at a Magnaflow or other straight through design, I have a set of 3.0x14 oval magnaflows on my Duster mounted between the rear sub frames and the outer 1/4 panels at the rear bumper, it is quiet at part throttle and non restrictive at WOT, not very quiet at WOT but it is not shattering windows I had a set of 3.5 Bullets on my 440 1969 Dart that dumped under the car straight out of the hooker fenderwells, I wanted to quiet it down so I added about 3 ft of 3.5 inch exhaust pipes in the shape of a V so it dumped in front of the rerar tires.That added pipe made a resonant(SP?) frequency that I was sure would break windows at part throttle bewteen 2700 and 3200 RPM Never again will I add pipes onto the muffs, mount the muffs way back as far as posiible