Hot Rod Dad,

I thought the question was about compression ratio, not displacement. If you milled .040 off the head, this would change the compression ratio...it would raise it.

If you turned around and sunk the valves in seats so they wouldn't hit the pistons, wouldn't you be doing the reverse of what you did when you milled the head?

Isn't compression ratio the difference (ratio) between the volume of the cylinder at BDC and TDC. If milling reduces the volume then wouldn't sinking the valves increase it again.

Is my thinking defective!

Stuart