MTFCA Forum

This gasket has holes for both of the center water passage openings.

The copper gasket has only one hole for the center passage.

Does the blockage of one opening have any significant effect?

Depends on your head & block match. Z head. others?

Here is my theory on it. Without the extra hole in the gasket, that gasket location has a comparatively large surface area. With the clamping force of the head bolts spread over that area, the force per square inch is probably at its lowest. Removing a section of gasket, which would otherwise "waste" clamping force by needlessly being compressed, would offer a better seal.

Steve, I think the extra holes, top, are for the water outlet and the water inlet.

I seem to remember a earlier discussion about the holes. It brought up the point of cooling. One theory was if both holes are open, then the cooler water coming into the inlet on the side of the block, tends to go into the first hole as the path of least resistance. Then takes a shorter path back to the radiator. That in effect starves the hottest point of the engine of the use of the cooler water. The hottest point is the area between the two center exhaust valves that are side by side. If the hole closest to the inlet is blocked off by the gasket not having the extra hole, then the coolest water tends to go across the engine block to the area between the two exhaust valves first. This tends to making the hottest point of the engine receive the coolest water first. Then circulate to the rest of the engine and then back to the radiator. I have always used gaskets with one hole if I can get them. I have never had a overheating problem. I have no scientific evidence to prove this, but it does make sense to me. Just my 2 cents worth. Your 2 cents and milage may very.