What makes aluminum heads produce so much more power?

[Rev]

After market head manufactures prefer Aluminum because its easier to cast and machine. That's the main reason. The increased heat transfer does minimize detonation somewhat and that's another plus. Iron heads will produce slightly more power in the same design though, just as Five0 said.

Rev

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'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.