you cant unless you reduce the combustion chamber to 100cc. I wrote that incorectly (sorry) I was thinking of some 604's that i am Dyno ing now . MY MISTAKE!!!! the 502's bored .030" had small dome JE's similar to the stock 502 pistons..

I also took my 99 HP 500 Carb motors in for vale spring replacement at 270 hrs. After a leak down test we decided to refresh both motors. When we got it apart 8 of the valves on one motor were cracked and near ready to break apart. The springs on both were weak but none of them were broken. The cylinders, piston's and all the bearings looked great. Based on what I have read all the HP500 valve trains are on borrowed time after 300 hrs. Replace the springs at a min.
By the way mine ran fine before I took it in, no sign of a problem.

PM any performance gains noticed after refresh?