[jgparker]

I agree that 1mm should give somewhere around .5 in compression increase, but this would change depending on your current compression ratio and stroke, and it is not linear. (Compression ratio theoretically goes to infinity as the piston to head clearance goes to zero.)

If you do not know your piston dome volume or you head volume, but do know your old compression ratio and your stroke, you can do a rough calculation of your new compression ratio as follows:

CRnew=

(Stroke X (CRold - 1))
-------------------------------------------------- +1
(Stroke - (DeltaDeckHeight X (CRold - 1)))

For a 2.7 with 70.4 mm stroke, a 8.5:1 CR and a 1mm deck height change, the new CR would be ~9.39:1.

The problem is you may not really know you current compression ratio. The correct way is to do it is with the full calculation in the previous post.