Originally Posted by articfriends

Thats a good question, they claim 25-40plus hp over stock manifolds , about 10 or 11 years ago I was running a blown 502 with 7 psi of boost, was still using stock merc iron manifolds, boat ran mid 70's. After 2000$ and a weekend of bloody knuckles, searching for 4" hoses, etc, I had installed a set of brand new lightning headers because they were supposed to be good for 400-600 rpm's over stock on a blown motor. Well, boat had a tiny more mid range punch but picked up ZERO top end, tried differents props, made zip difference, I couldn't believe it! I am sure that at a certain amount of cubic inches and or boost that stock manifolds would just kill the power of a engine but you would be surprised on a un-modified engine how little difference it really makes, I think 1/2 the gain is from the weight loss on stock apps!