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Overrun ignition retard

MoTeC M1 Software Tutorial

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Please explain why the ignition may be set to retard during overrun when there is no combustion.


It helps to drag the engine speed down and smooths the transition when you come off the throttle, than if the timing was left in Normal and throttle was the only control.

It also helps generate pops and bands on the overrun if you want it.

I understand your first paragraph, but the second one not quite because for pops and bangs we would still need some fuel mixture in the exhaust, or is what you are saying that there is some residual unburnt fuel left from prior to the overrun shutoff event ?


I just realized that the thread title should carry the term "during fuel shutoff" as well. Apologies if I have caused any confusion and thanks for the answers.

The residual fuel comes from the fuel film "puddle" being drawn through the engine and consumed.

that makes sense, thank you very much.

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