10.5:1 273 pistons with 360 heads compression ??

To get 9.1 compression, you will need a clearance volume of 69.3 cc.

This means that you should have 69.3 cc "above the piston" at TDC. This includes the volume of the head combustion chamber, the volume of the head gasket and the volume above the piston.

Standard 360 heads that I've measured are 72 cc's.

the head gasket at 3.70" bore and .028" thickness is 4.9 cc's.


So you will need:

72 + 4.9 - 69.3 = 76.9 - 69.3 = (-7.6 cc's)


This means that your piston must displace 7.6 cc's above the head deck.

Using 3.63" for the bore, you will then need your pistons to stick up .043 inches ABOVE the head deck. This assumes a flat top piston.

For a flat top piston to be 9.1 - 9.5 compression, it will need to stick up .043" to .062" above the deck. If you want to use pistons with a dome between .043" and .062" and you will have to take a little off for valve reliefs.

The piston will need to stick up a little higher to compensate for the valve reliefs. So an educated guess, that pistons with valve reliefs should stick out somewhere near .050" - .067" range.

Put your piston in the block and see how far it sticks above the deck.

If you use 360 heads, you will need a piston that sticks up above the deck about .055" average (give or take a little).

If you don't have pistons that stick above the deck, then you will want to use the 273 heads to keep your compression up.