I'm running a set of Clifford street rod headers along with an Offy 4 bbl intake on my 250. The flanges on those headers are fine in my opinion.
The only trimming I had to do was on the Offy's cast flanges as they are not what you'd call perfect. The fit in between the Offy and Clifford flanges was not all that bad and was easily adjusted with a coarse file to the Offy.
The biggest amount of fitting was in thinning the OUTER faces of the Offy flanges at the runners so the retainer pieces would bear down evenly against both manifolds. You'll also want to unscrew the studs at the very ends of the head and replace them with regular threaded studs so you can get a good seal on the header ends. be sure to put some silicone or other sealer on these 2 studs as they enter the water jacket in the head. The rest of the studs go into blind holes. End studs are 3/8 x 2 inches and the rest are 3/8 x 2 1/2 inches. Those will allow you to reuse the original Chevy manifold retainers.
Total time for trimming the manifold and stud replacement was under an hour on my engine.
Mike G ( 4355 )
