Aluminum Heads ?

Car craft did a dyno test with the exact same combo on a small block chevy. One with aluminium and one with cast cast. They flowed the heads and the flow was very close to the same. Same combustion chambers and everything. The results show 2-4 hp difference and that 2-4 was swapped through the rpm range between the two heads. I don't think the cast iron head will make more power given all things being equal.