I was looking at the newer GS450h and saw that it had 13:1 compression versus the 11.8:1 compression. But I looked through the parts catalog and everything is basically the same part number, same exact numbers for pistons, rods, crank and head. Anyone know why it's listed like that?

 

Smaller combustion chamber volume in the head will do this. No need to change anything on the pistons that way.