as referenced from the link shared above (thanks for that), this graph pretty much sums it all up - the bottom line being there isn't a huge difference between 318 manifolds and headers...at least not enough that I personally will care. This is the results tally from the Motor Trend LA 360 crate motor exhaust manifold comparison. Yep I'll use my nice, simple, quiet, good-fitting 318 manifolds I already have