Does gasket thickness affect "quench"? Say ~.040 gaskets were recommended to acquire the preferred quench area, then the heads were milled .020 more. Does this mean that you would need a .020 thicker gasket (~.060) to keep the approximate same quench area as with the thinner gasket/no milling?

 

The quench distance is the compressed thickness of the head gasket plus the piston deck height. As long as the gasket thickness and the piston deck height does not change (decking the block,etc.), then your quench distance will remain unchanged. Milling the deck surface of the cyl. head does not effect this "quench" distance.

 

And to build on what Jason99TA posted, adding the extra gasket thickness actually hurts you on quench. It seems like an OK way to make up for the lost surface milled away on the heads, but it's not.

0.020" height of head surface exposed to the piston crown is part open chamber area, part flat quench area. That same 0.020" of head gasket is all wide open space...detonation waiting to happen.