Compresion changes

volume

Volume of your head gasket = bore x bore x 12.87 x thickness of head gasket.

Usually head gasket is .003 oversize of the actual bore. ie 4.375 bore has a 4.400 gasket usually.

Then plug that number into the compression formula:
(comb chamber cc's + gasket cc's + deck cc's + (displacement x 2.0483)) / (comb chamber cc + gasket cc + deck cc)

simplified that is the volume you would get if you poured the motor x (displacement x 2.0483)/volume you would get if you poured the motor.

Even if you haven't poured your motor, but you estimate 10:5 to 1, you can work backwards with the formula with your known engine displacement to get your 'poured cc' then figure up how much changing your gasket cc's would effect that number.

If you have a NHRA rulebook somewhere, all those handy formula's are in the back...

If I remember correctly you run a 451 Don, so do the math, but on a 4.375 bore 451 cid motor, .010 on gasket usually equates to roughly .25 of compression ratio. Compared to a 521 motor with 4.4675 bore, it's almost .33 of a point on .010.

Hope that helps.