What type of exhaust was in the 455 stage1? Factory headers or manifolds? I have original 455 manifolds on my 70 455 from an electra. How restrictive are these? I really don't like headers because they often leak and I also like a factory look. I have a 69 slylark and if a person did not know that they didn't make a 455 for that car in that year it would appear that GM put it there.
Greg Gessler provides a service where he ports stock manifolds that flow very well. He has them on his F.A.S.T. car that currently runs 11's....this may be something for you to investigate if you do not want to go to headers. That said, when I replaced my stock 400" motor in my GS with a healthy 462" motor I originally hooked it up to the stock exhaust manifolds and stock 2 1/4" exhaust system. The improvements where not as great as what I had expected, going from a well worn 90,000+ 400" motor to a Stage1+ 462" one. A few months later, I replaced the whole exhaust system with 1 7/8" TA headers and 2 1/2" mandrel bent exhaust pipes with Dynomax UltraFlo mufflers. With no other changes at all, the car picked up exactly 9/10th's of a second !!! The stock exhaust system was literally choking the motor's performance. An engine is basically an Air Pump - restrictions in OR out will hamper performance significantly
Headers, Headers, Headers... If it's performance your looking for, headers are the only way to go. Leaks only happen on low quality headers and/or poor installation. If it's the factory look you want, go with the manifoldts and/or check into porting with Greg.
