I too have spent way too much time with a noisy, smelly, messy, love to burn you dyno and have noted this. On billet aluminum heads and blocks that have no cooling jackets equal power can be obtained in relation to iron counter parts. We make our own for the pull truck and tractor so we can control each step of the process and make changes if it offers improvement in power or durability. On heads with coolant passages the more timing and compression that can be used with the aluminum without detonation makes the power output on par with the iron heads. BUT, as Jerry said, the very reason more timing and compression can be used is because the heat (power) is being carried away so it's a wash. When it comes to durability on high mileage street driven machines using the old generation 1 heads and blocks then iron wins hands down. Now when one gets to the LS series GM and the Modular Fords then it's a whole different story. All the sensors, monitors, control modules, and computers can keep the combustion process precisely correct no matter whether it's iron or aluminum and do so for several hundred thousand miles. I'm one tick from 80 years old so I'll GLADLY hand off this rats nest of circuit boards and wires to the next generation of rodders.
