Im looking on summit for head gaskets and ive noticed that they have different bore sizes. My 350 has been bored over thirty thousandths so would I want the bigger 4.200 in. bore or do I want the standard 4.166 in.

*edit*
i would use the search feature but i cant :\

 

You want the smallest bore size gasket that doesn't overhang the cylinder bore.
The bigger the bore size of the gasket the smaller the border between cylinders. Gaskets are made to fit the "most" applications to cut costs.
400 block +.030 overbore = 4.156 , gasket size 4.166
400 block +.060 overbore = 4.186 , gasket size 4.200
350 block +.030 overbore = 4.031 , gasket size 4.060
350 block +.060 overbore = 4.061 , gasket size 4.100
So you can see that a 4.200 "will-fit" any of these applications, but will not be ideal except for one.

 

What would happen If I use a 400 gasket on a 350 engine..?
I assume some compression loss, but might be that small that it would not matter..?
And it should not shorten the gaskets life..?

(yeah, I know, an old thread ;-) )