i did not know such a thing existed, to check that i would have to measure wrist pin height , correct? That is the distance from pin center to top of piston and check that against factory specs. The pistons are marked Std. and .04 so i believe they are a standard piston just .040 over. I can certainly check though. I am still puzzled by the large volume of my combustion chambers on a non ported factory high compression head. I am going to pop in my new valves when they arrive and measure with a 50cc burete next time i cc the chambers. Thanks for the tip!