We have built several stock resto type engines for customers that we extrude honed the intakes and exhaust manifolds. No before and after dyno comparisons, but they all made good power when done. Problem is the extrude hone process costs more that the actual manifolds do. Yes, it is pricey. For those looking for every h.p. but stoll looking factory such as the F.A.S.T guys the money is probably worth it.