Tech chat w/ Marc Matzer
The valve relief cutouts are not the only thing on a piston that affects the compression ratio. The compression height of the piston (measurement from center of wrist pin to the top of the piston) affects the deck clearance. The information that I have shows that the 1800 piston has a shorter compression height (increased deck clearance) than the 2000 piston, which has the effect of making the compression ratio essentially the same with either piston. Apparently the increased compression height was used by Fiat to offset the deeper flycuts in the non-interference piston.