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#65584
Pete Muller
Participant

Ric,

Absolutely correct — here’s what happens:

Retarding the ignition timing drives the exhaust temp up significantly, which *increases* the speed of sound.  This causes the exhaust pipe to “act” like it’s shorter than it really is (allowing the engine the engine to rev higher).

Ideally, the exhaust would be adjustable, and the ignition timing would stay the same or even be advanced a touch at very high revs, but since most classes have a fixed exhaust rule, retarding the timing tricks the engine.

PM