Alloy heads

My understanding is that because heat is a major component of detonation and aluminum dissapates heat better than cast iron, this makes them less prone to detonation.
If all things were equal, an engine with aluminum heads would be less effective due to the loss of thermal energy. Cast iron is better at heat retention and keeps the fire in the hole longer whereas aluminum absorbs and dissapates the heat. Perhaps this is why you can bump up the compression with aluminum and retain some heat for the combustion process, putting that heat back in the hole where it belongs and not losing it through absorbtion.