I learnt from the past that the rallycross cars ran between 0.4 to 0.45mm plug gap when tuned to produce 700-800 BHP.
Your result was consistant with plug gap. If the plugs were biscuit brown with some black markings, it appeared that the fuel didn't have enough time to finish burning before exhaust valve was opened. It could be ignition timing related or still a small amount of mis-fire.
Do you have means of advancing the ignition or reduce the plug gap further?
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Richard L
aquamist technical support
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