My old pump gas street Duster would loose .0003 to .0005 E.T. and .2 MPH with the full 3.0 inch exhaust system on that car, I think the differences was the lighter weight, the muffs were mounted behind the rear end between the 1/4 panels and stock rear sub frames, the head pipes ran under the rear end housing directly from the Hooker A body B engine headers were fender well exit with 1 7/8 primary pipes and 3.5 inch collector-

Be careful when testing the new combo please