deadeyejedi

what size head gasket bore should i buy for my .030 over 455 build ?would like to go with cometic and part number would be helpful.i assume .030 over on the gasket as well ? i would like the .027 thickness to maintain my targeted compression ratio.

deadeyejedi

after doing some research i think i answered my question .cometic offers a 4.200 bore .027 thickness head gasket for the 455 olds. if my stock engine with a 4.126 bore was bored 0.030 over my new bore should now be 4.156 ?i assume going larger with a gasket bore size would be better than going smaller.

BillK

Correct. One thing that a lot of people don't take into account is the amount of chamfer your machine shop put on the top of the bores. Even a .030" chamfer adds .060 to the bore size when choosing a gasket. In your case you would add .060 to your bore size for a final size of 4.206" Most of the Cometic gaskets don't seal right at the id of the gasket so the 4.200 one should be ok. To be sure measure the od of the chamfer and then call Cometic and ask them to be sure. They are very decent to deal with on the phone.

B964

Replacing head gaskets on a 455 with stock bore size. Any problems using Mr Gasket 5788G? They are listed as being 4.230 bore size and .038 compressed thickness.

cutlassefi

Nope, I use those all the time.