The rules stipulate the heads can't be ported. The 502's oval-port heads (PN 12363399) have good-sized 290cc intake runners and 110cc exhaust ports, along with 2.25/1.88 valves. With the stock-type, small-top pistons, this motor's compression ratio is 9.84:1. That's great for the street, but a race engine could always use more. Unfortunately, the rules forbid reducing the combustion chamber volume, which would increase the ratio.