1973 GTO , 406" automatic 3.23 posi setup with stock #13 heads and Summit 2801 cam. The stock exhaust manifolds with 2" full exhaust and AP turbo mufflers ran 15.2 sec @90 mph. Engine done by 4500 rpm. I changed the exhaust over to Ram Air reproduction manifolds with 2.5'' openings and 2.5 inch full exhaust with Dynomax Super Turbo mufflers. Car ran 14.7 @94 mph and pulled right to 5000 rpm shift point. Power speed calculator said engine went from 250 to 285 net horsepower. Driving it has much more throttle response and a nicer sound.
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