What?

There are anecdotal sayings that aluminum will support higher compression, but the only data I have seen doesn't necessarily support that.

Years ago one of the hot rod magazines did a dyno test to compare iron vs aluminum heads. They got one of each from the same manufacturer that were as identical as possible.

They tested for heat related differences primarily, they found nothing outside the margin or error with either head and multiple coolant temps.

When it came to compression tolerance the engine tested was almost 11:1 and showed no signs of detonation with either head setup and they were running 91 octane.

Now this was a dyno test only, who knows how it would act on the street.

Dyno test article