90 over 318 Head Gasket info needed !!

skrews said

Don't use a 4" bore gasket on a 4" bore block the fire ring will over hang the cylinder bore after chamfering the block to drop in the rings. I'd recommend a 4.08 gasket.

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Yes, I went to 4.125" with a set of Cometics on a 340 over bored to 4.060". There will also be some small mis-registration of the chambers on the bores that will require a slightly larger gasket bore hole. So the 4.080" recommended above is the most suitable size for your use here IMHO.

The Cometics can be had in quite a variety of thicknesses and bore sizes too, starting at .027" thick.

Go here:
https://www.cometic.com/c-1280258-automotive-domestic-mls-head-gaskets.html
Then enter your engine type and it will pop up a whole list of MLS head gaskets for the LA with their whole variety of thickness and bore hole sizes.

Be aware that the head and block surface finishes need to be in a certain range for these MLS head gaskets. So keep that in mind. The info is somewhere on the Cometic site.