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What are the gas grades in non CA states? Ours goes 87, 89 and 91 and of course diesel where available. Every M3 in CA runs their lifetime with 91 and we know nothing better so it is the norm.
OBD II cars from 1996-present all have knock sensors. With a high compression ratio of 12.0:1, without knock sensors, there would be a lot of premature detonation in the cylinders because low octane fuel can't be compressed to those ratios without spontaneously igniting...however being a post 1996 car, the ECU will immediately retard the engine ignition timing. This is just a guess but it probably ignites the compressed fuel air mixture early so it doesn't do it automatically. Though I'm not sure how this works since you can't change how far the piston extends into the top of the stroke. Anyone care to chime in?
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