1969 Dart 440,727 12.23 at 109.6 with a set of 2.5 turbo mufflers feeding directly out of a set of Hooker A body (2 inch x 3.5 collectors) fenderwell headers with a short side pipe coming out in front of the rear tires. I removed the exhaust from the headers back and the car ran 11:39 ET at 117.75 MPH on the next run in a 1/4 mile My Duster had the same headers with a three inch pipes feeding to a set of Magnaflow 3.0x14 long oval muffs mounted at the rear bumper and the car only pick up .04 ET and about a 1/4 MPH increase in the 1/8 mile, probally due to the weight removal I haven't tried removing the exhaust at a 1/4 mie track yet on the Duster