While you're at it, you should port match the port openings to a felpro 1404 (I think ) exhaust gasket, which is easily done with a die grinder and carbide bit. I spoke with Randy Brzyzinsky of Brzyzinsky racing and he mentioned that if that is done, there is no restriction on your exhaust port. There is no need to port the inside of the manifold, just the port openings according to him. They also sell a mandrel bent 2 into 1 exhaust system which makes much more HP than duals. I bought it but have not yet installed it.
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