OMC King Cobra 454 intake manifold gaskets

[Noldisx]

Hi community

In the intake manifold gaskets from the OMC king cobra 454 there are 2 removable metal closing caps to close the exhaust channels which goes through the heads. Now I have 2 different versions. One is with a small hole and one is fully closed. Which one should be used?
Or leave them completely out of the gasket?
What are these plates good for? Can it cause heating of the intake manifold without it?
Thanks Noldi

 

[Maclin]

Those plates are to block off the exhaust crossover under the intake plenum floor, this is a racing performance "trick". In full duty cycle engine usage you need the heat to keep the fuel/air mix in a vapor state for best economical results in the wide range of conditions that engines experience. If the engine is only raced then the racer may want the engine to see a cooler denser mix for a short period of time, and the block off plates are used. The plates with the small hole let in less exhaust thus heat for other race conditions where you want the heat just not all of it.

We need some more expertise to join in for this particular usage. My opinion and experience is that the block off plates would not be used.

I did try this in a performance car once with a stock cast iron intake manifold. It kept gas-fouling spark plugs. I only raced at a track occasionally and drove it as a daily driver and had to remove the plates.

 

[Lou C]

Given that marine engines run cooler than the automotive equivalent by approx. 40-50*, I would be inclined to not use the block off plates because with an engine temp of only 160* especially in cooler weather, the engine will run better if the carb is kept a bit warmer by heating the intake. On some engines, the heated crossover also was used to provide heat for the choke spring so it opens as the engine warms up, but on later OMC engines they used mostly Holley carbs that used an electric heated choke. So, leave out the block off plates.