[scottj]

Higher rpm's (above 3000) will keep the Chevy purged of steam which is why steam holes aren't used on a race engine. The big problem is that the center exhaust ports are too close together on the Chevy. This causes a hot-spot that increases relative to power. The aftermarket came up with the spead-port exhaust and we run external coolant lines to remedy the problem. The exhaust port location and the resultant problems like blown head gaskets and cracked heads was one of the major design considerations when Chevy went to the drawing board to design the canted-valve and then the SB2 head.
I don't believe the Ford head suffers from this cooling related problem.