10:1 is about the high end of the typical. But motorcycle engines sometimes go 12:1 to 14:1 with 87 octane, mostly because their heads run cooler.

The spark timing is definitely an issue, but I was pondering about the compression-induced pre-ignition, which is triggered by sufficiently hot hot-spots of the cylinder where the fuel/air mixture is in contact.

Reducing the spark plug heat range does not change the heat of the spark. It only changes how fast heat is dissipated into the engine head, which, in turn is cooled by the coolant fluid. If the pre-ignition triggering hot spot can be removed by (1) a colder heat range spark plug and (2) lower head temperature via a lower temp thermostat, then I suspect that the engine could successfully run 87 octane without ill effects.

Another thought would be to use water injection to cool the intake air, thereby possibly reducing pre-ignition.

Any informed opinions (either by direct experience or auto engineering background) would be appreciated....

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