trying to figure out the "ata" gauge

[Babi]

did a little testing on detonation with the spit mkIIa.

sea level, throttle to max, boost cut out (the instrument was reading +9, but that's the max), pitch to a minimum (1700 rpm). the plane flew on for 20 minutes. no damage. I thought this was the worst possible scenario for detonation (max pressure, min rpm).

did the same thing with max rpm (3100 rpm) this time intermittent black smoke appeared, (that would go away if i put boost level back to +6), but again no damage. after another 15 minutesi grew tired and closed the radiator, which led to "perforated water radiator" in a few seconds.

what am i doing wrong? i thought the engine were much easier to damage.