Really? How many completely identical sets of heads with all other things being equal but the material they're made out of have you seen dyno back to back from one and other to prove this claim? I realize what you're saying. Higher heat in a more thermally efficient combustion chamber = higher energy production....and if we were all running around with our tanks full of C16, I wouldn't have a problem with your logic. But the fact of the matter is that pump gas....especially today's pump gas (being as full of ethanol and other impurities as it is), will not produce that kind of energy without creating some serious pre-ignition issues. Issues that will either prove detrimental to power production, or the engine itself unless a measured amount of timing is removed. Aluminum heads will allow for more aggressive ignition timing and fuel curves and carry power levels further on the fuel that is available at the pumps today. Do you think manufacturers like GM or Dodge care about an additional 45lbs over the nose of a car that's tipping the scales at nearly, or above 4,000lbs as it is, if iron heads were far superior? Why would they bother running a more expensive and complex aluminum head if cast iron heads that are not only more durable and cheaper to produce also made more power? I agree. There is power to be gained with heat, but so too is there power to be gained with timing. In the case of these two material choices, only aluminum will be able to take advantage of both given the standard of fuel we've got to work with.