Not sure why you seem stuck on 4bbl? Just how much flow (HP) do you figure you need? However, so far as I know, any of the TBI 4bbl systems will operate 4-6-8 cylinders or more.
Well I met a older guy at a local meet yesterday that has a offy 4bbl manifold and a set of headers thats been collecting dust in his attic for a couple years and said hed like to get rid of it. Seeing as im the only game in town running a slant 6 anymore i told him id take the manifold and headers off his hands. Doing so and talking with a couple of the guys at the meet who have done the small block and big block swaps, and tbe general consensus was build the slant up for a little boost and throw a turbo on it.
