I was planning on getting a GSR motor and I was advised to swap in some ITR pistons to raise the compression; now my question is which is better standard size or oversized? I didn't know there was a difference, can anyone explain the difference in the standard or oversize piston?

 

Oversize piston is slightly bigger then standard. The one that came with your gsr motor is standard size and of course oversize is always better compare to standard. The reason they make oversize piston, is for motor with worn out cylinder wall. If you go w/ oversize piston, your block need to be bore out. I hope that helps