The higher the rpm and the more your intake/heads/cam will flow the more h.p. you will loose through the sidepipes. My ERA 427 side oiler, 428 crank with solid roller cam, dual carbs, high rise heads, 12.5 to 1 compression lost 97 horse power with the sidepipes in place! I've run the car with and without the sidepipes and you can really "feel" the difference with open headers (but you need two sets of ear plugs, man that thing is loud)!
