2.2L cylinder cc'ing help needed

[edbaus]

Looking to make some 2.2L pistons for a turbo.

What I need to know is what the dome cc's are supposed to be to give me about 7.3:1 compression ratio.

What I have heard is that the heads (2.2L twin plugged) are approx. 69cc's

The piston skirt gap is 1 mm.

If this is correct, then it looks like I need a 9cc dome.

This seems odd. I would have thought I needed a dish.

Anyone see a problem with my calculations?

Thanks

Ed