Head gasket
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Instructor
Joined: Feb 2022
Posts: 203
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Head gasket
Just put my 327 together.as I was cleaning up my mess I picked up rapper from head gasket.it said for 400sb they sent wrong gaskets.the engine is all together.will I have a problem with that head gasket.
Le Mans Master
Joined: Feb 2014
Posts: 8,934
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From: Richardson Texas
The difference between the 400 and the 327 are steam holes for cooling due to the siamesed bores on the 400. The 400 gaskets should work but you'll have an area around the cylinder, that the bigger gasket bore, will leave exposed.
Le Mans Master
Joined: Feb 2008
Posts: 6,505
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From: Folsom CA
It will reduce your compression a little as the 400 is a 4.125 bore and the 327 is a 4.000 bore. Could you run it, yes, I think I would change it out for the proper size. Fel Pro 7733PT2. Or you can get the thin steel shim gaskets like the factory used and raise your compression a little more. Running that oversize gasket will leave some un burned fuel in your cylinders every time the engine fires, a very small amount but you pay for fuel, might as well burn it for power rather than exhaust waste.
Last edited by Westlotorn; Feb 12, 2024 at 08:09 PM.
Burning Brakes
Joined: Nov 2017
Posts: 780
Likes: 112
From: Redneck Riviera, FL
can't speak to how accurate this is but it will allow you to play with head gasket bore diameter to see the effect on compression ratio.
https://diamondracing.net/p-10-compr...alculator.html
https://diamondracing.net/p-10-compr...alculator.html
Le Mans Master
Joined: Nov 2003
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From: Maryland
St. Jude Donor '05, '09, '15
Tom
Le Mans Master
Joined: Feb 2008
Posts: 6,505
Likes: 1,926
From: Folsom CA
The Fel Pro 7733PT2 has a bore size of 4.125, the Fel Pro 8364PT has a bore size of 4.190
So the 400 gasket in this case is .065 larger bore than a 327 gasket. Both are nominally .039 thick. The use of the 400 gasket is not fatal, it will work, you are just leaving some performance on the table.
If you don't run for maximum power you might never notice the gasket change. I doubt the change would net more than 15 HP if corrected.
7733PT2 picture
So the 400 gasket in this case is .065 larger bore than a 327 gasket. Both are nominally .039 thick. The use of the 400 gasket is not fatal, it will work, you are just leaving some performance on the table.
If you don't run for maximum power you might never notice the gasket change. I doubt the change would net more than 15 HP if corrected.
7733PT2 picture
Last edited by Westlotorn; Feb 14, 2024 at 01:10 PM.
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Instructor
Joined: Nov 2011
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The head gasket must fit the combustion chamber as well. (Either the bore or chamber, whichever is larger.) Without mention of the head used, you need to look close there. No portion of the gasket can extend into the chamber or bore and survive or create detonation issues. This is why you see non-round head gaskets. Typical SBC in stock trims will be about 4.100-4.125". The steam holes only matter if the block and heads are drilled for them.
Brandon Unklesbay
All-In Performance, LLC
Brandon Unklesbay
All-In Performance, LLC