I understand what compression is, but when people buy 'High compression' piston, what changes the compression? is it the shape of the piston, length, width??

Thanks

 

see any differences

 

Compression is the relationship of the top surface of the piston to the head at bottom dead center and top dead center. It is a direct ratio of how much volume is available when the piston has traveled all the way down, and then how much it has been compressed when all the way up. Pistons, rods, crank,bore, head, and head gasket can all effect the overal compression ratio.

 

Yea i know that, just asking about the difference in physical properties of a piston...

 

Yea ones is flat the other looks cone topped? Which one makes more compression and why?

My guess would be the flat top one because it can go higher into the head?

 

its the volume in the cylinder at tdc and when its fully down

 

You guessed wrong.