[chopper]

ERA 535:

Actually, I called Southern Automotive and talked with them (they built my engine and installed the Edelbrock heads). They said to subtract 0.012 from the iron head specs. Being basically a coward, I fudged that a little and subtracted 0.010 and went with the 0.014 number. When hot, I measured them and came up with the 0.024 clearance. It all seemed to work out OK.

Jack Z:

The correct answer is that the aluminum alloy heads expand more than the steel pushrods. This pulls the rocker arms further away from the camshaft when the engine heats up; hence the increased hot clearance.