a good guess from my calculator would be .3-4 increase in CR, thats assuming that the dish volume and piston height are the same on all the Mahle pistons(std and overbore)
Compression ratio is figured out by= (cylinder + chamber volume) divided by chamber volume. That's the formula in Mopar's 2.2, 2.5 FWD Performance manual- chapter 13 Racing formula's. That said, you'll have around 8.3 w/o the shim.
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