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19nova72 07-07-2005 09:43 PM

400 small block compression and head gasket question
i took the heads off of my 400 sbc today to inspect the pistons and get ready to swap the cam. My motor is from 72 and it has a dished piston. My friend gave me a burnt piston from a 400 (year unknown) that he had and i compared the two pistons. On his piston there are deeper valve reliefs and the outer edge of the piston has less material than the pistons in my motor. I was wondering what compression ratio my motor might have. The code on the front of the block is T0526CKP and the number on the back of the block is 39511511. Its a 4 bolt main block. Ive read that 400s had anywhere from 8.5:1 to 9.0:1 compression ratios. I was thinking that I might have one of the higher compression 400s because of there being more material on my piston. Also what is the purpose of the small hole on one side of the top of the pistons?

Also Im not sure if the head gaskets that came out of the motor are stock or not. They almost seem to be a permatorque type gasket. They may be a regular steel shim but im not sure. Either way, i measured them to be about .030" compressed. I dont want to lose any compression in the motor so i want to put at least an .030" gasket back in or something not much thicker, preferably a little thinner if possible. Does anyone have any suggestions on what gaskets i should use? Ive looked in summit but i havent found any with a thickness close to .030" with a bore for a 400 with the steam holes. Any help or suggestions are greatly appreciated.

bracketeer 07-07-2005 09:48 PM

Look under the piston. You may find a manufacturers name. If so you may be able to get a matching piston. If you use a piston with more or less meat. You are going to put your motor seriously out of balance. If I understand correctly. The small hole in the top of the piston designates (front). The hole goes towards the front of the motor. I would just use a Felpro 400 head gasket. With dished pistons and stock 76 cc heads a .020 head gasket isn't going to do a thing for you.

NXS 07-07-2005 09:49 PM

GM has some steel shims that are .026". I'm not sure if they had steam holes but with that type of gasket it would be childs play to drill them.

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