This may be a dumb question but on a Buick 455 are the end rails of the block (front and back) under the intake manifold sealed for vacuum or oil leakage? I was always under the impression that these seals were for vacuum until a friend of mine told me they were for oil sealing. The more I thought about it the more he seemed right because that area where the valley pan sits should be under the same pressure as the crankcase which pulls air in from the breather on the valve cover. Am I missing something?
Just a curiosity question. Thanks.