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Pre-ignition and detonation are 2 separate issues. Given that you have increased the compression and are running a good ignition system, my bet is detonation. Jerry Woods told me 30-32 deg with a stock 2.7 was pushing the limit with todays fuel quality. Detonation sounds like someone pouring a shovel full of pea gravel on a corrugated metal roof, with an accompanying dramatic power loss. Detonation damage is cumulative, each event adds to the total damage. Reducing the advance and adding octane boost will help determine if it is detonation. Doubt it is pre-ignition.