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...wanted to add, that obviously, the ECU can't protect the engine against pre-ignition.
Detonation/knock is the spark being fired too early. I.e. the ECU can intervene and change the ignition timing.
Pre-ignition is uncontrolled burn prior to the spark being fired. I.e. some other source sets off the combustion. E.g. hot spots in the combustion chamber (as an example carbon buildups or the spark plug itself being so hot that it's glowing).
Not sure what kind of pressures are required to make 87 octane auto ignite, but probably even our high compression ratio would be far less. Mazda's new Skyactiv-X engine (compression ignited like a Diesel) has a compression ratio of 16:1 and runs on 87 octane. You would probably need to add boost into the equation for that to be a problem with the FA20.
I would, however, suggest to run the engine fairly rich at wide open throttle (11 AFR) for the cooling effect of the excessive fuel.
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