Turbo boost and octane

An octane rating is a system by which a fuel is rated to resist knocking and detonation in an engine.

A high compression engine compresses the air-fuel mix, raising the temperature more than a low compression engine…high-temperature is what causes K&D.

Pre-pressurizing the air-fuel ratio with a turbo or blower also raises the intake’s temperature.

An intercooler…a heat exchanger used to cool the intake charge…
can alleviate the problem a bit.

If we could design an ideal intercooler, one that could reduce the intake charge to at or even below ambient temperature, could we still run the boosted engine with a lower octane fuel as if it were an unboosted engine?

Probably not. Unsupercharged engines are troubled by detonation if the compression ratio is too high for the anti-knock rating of the fuel. The intake mixture temperature of unsupercharged engines is pretty low because of the evaporation of the fuel. When the cylinder pressure is raised on the compression stroke the temperature goes right up with it.