Most stock replacement pistons have offset pin holes. The direction they install unloads one side of the piston more to reduce any noise such as piston slap. It's when you reverse the pistons to throw the offset the "other way" that it unloads the piston and frees up a little HP. Centered pin holes achieve the same thing. All HP pistons such as hypers and forged have the pins centered...at least all that I am aware of.
