isnt the piston a 13.5 to 1?

 

the bore is 95 x 63.4 mm, the COMPRESION is 11.4:1

 

Nope. 13.5:1 would be a healthy bump in compression.

 

sorry i am new at this. so that would make me go faster top end? or help me get there faster?

 

Gearing is usually the limiting factor for the 450 class and open class sport quads for top end speed. The YFZ has enough power to pull the top of 5th stock but you are going low 70's at that point, not real useful for trail riding or mx/xc racing. Desert or drag racing
may warrant gearing more for top end but 90% of riders will never use wot in 5th often. Bumping up compression will give you a power boost across the board, usually most noticeable at 1/2 throttle and less though. You will get more low end grunt, which should give you better acceleration. A lot of engine builders will use this property of high comp pistons to offset the use of a mid-top end cam(s). The downside is that at 13.5:1, you can no longer using pump gas.