Catastrophic detonation is not related to fatigue.....You said "I think fatigue is the reason why most old sti has piston failure" - You are not correct in your assumption......Most of them Die from big end bearing failures.

The STI Bug in question failed due to a leap in Volumetric efficiency that the ECU was never designed to compensate for, which probably lead to severe DET.

Detonation is a pressure spike with enough energy to crack cylinder bores, bend conrods & shatter pistons.

Engine Detonation causes a very high, very sharp pressure spike in the combustion chamber but it is of a very short duration.

The sharp spike in pressure creates a massive force in the combustion chamber. It causes the structure of the engine to ring, or resonate, much as if it were hit by a hammer. Resonance, which is characteristic of combustion detonation, occurs at about 6400 Hertz. So the pinging you hear is actually the structure of the engine reacting to the pressure spikes.

The high impact nature of the spike can cause a clean fracture of the ring land, bend conrods and fractured valves-intake or exhaust.

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