Head Gasket Bore Diameter

[Eazy_P]

I have a 351w block that has been bored 0.040 over (4.040").

I will be using Cometic MLS head gaskets, but am unsure which ones I should buy since they come in 4.060, 4.080, 4.100 bore diameters. I know the gasket bore needs to be larger than the cylinder bore, but I'm not sure how much bigger I should go.

Anyone have any suggestions of which ones I should get?

[BigLeo69]

more bore on the head gaskets changes your compression ratio (CC's)
i would think that the cometic guys would have one for the 40 over

keep the compression of gasket around .040 thickness

[Eazy_P]

Thanks Leo, I will be going with the .040 compressed gasket.

I want to keep the gasket bore diameter as small as possible, but I'm not sure if the 4.060 HG bore is big enough to cover the taper at the top of the cylinder bore or not (especially if the cylinder bores are not exactly centered). Just wondering what size head gasket bore most guys are running on a small block ford that is bored 0.030 or 0.040 over.

[Wade Chamberlain]

Originally Posted by Eazy_P

Just wondering what size head gasket bore most guys are running on a small block ford that is bored 0.030 or 0.040 over.

4.1"

[Eazy_P]

Originally Posted by Wade Chamberlain

4.1"

Thanks!

[Daddy-O]

Gonna catch hell for this but with the 4.020 SBF and aluminum TW heads I use Fel-Pro 4.100 / .047 gaskets.
Fel-Pro Q9333PT1 - Fel-Pro Head Gaskets - Overview - SummitRacing.com

[Wade Chamberlain]

why would you catch hell? That's a good gasket.

[DeaconBlue]

Personally I would keep the HG bore as close to the block bore as possible - in your case the 4.060" bore. The larger the HG bore compared to the block bore, the more compression you loose and the more area you have for carbon deposit build up and hot spots.