Intake manifold pulling oil
The front and rear horizontal block surfaces under the ends of the manifold are called the "China Walls". These generally have a pin in them to assist with end gasket retention. There is a corresponding hole drilled in the bottom of factory manifolds that acts as a relief for these pins. The problem is that many aftermarket manifolds do not have these holes drilled in them, and when you try to install the manifold it is not allowed to tighten down properly, since it is being propped up by the pins. The common solutions are to either drill the bottom of the manifold ends in the proper locations, or remove the pins entirely and retain the end seals with RTV or just use a thick bead of RTV instead of the seals.
The front and rear horizontal block surfaces under the ends of the manifold are called the "China Walls". These generally have a pin in them to assist with end gasket retention. There is a corresponding hole drilled in the bottom of factory manifolds that acts as a relief for these pins. The problem is that many aftermarket manifolds do not have these holes drilled in them, and when you try to install the manifold it is not allowed to tighten down properly, since it is being propped up by the pins. The common solutions are to either drill the bottom of the manifold ends in the proper locations, or remove the pins entirely and retain the end seals with RTV or just use a thick bead of RTV instead of the seals.