I am not sure I completly understand compression distance. I was looking at two pistons one had a compression distance of (Speed pro Hyper) 1.560 and the other 1.540( Silovite Cast). I was told by an engine builder that the Speed pro would not fit because" the ring sits too high" and he told me that is why he used the Silovite cast insted. Does Compression distance have anything to do with this or is this guy just feeding me a line of bull b/c he charged me for a more expensive piston and put in a cheper one? When building the engine he told me the deck was perfect.

Basic set up:

350 .30 over
dart s/s 165cc heads
rods 5.7" inch

 

the compression distance (hieght) is from the center of the wrist pin to the top of the piston. if the block is zero decked with the 1.540 pistons then the 1.560 pistons would sit out of the deck .020". that is why he probaly put those in.