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Overrun ignition timing

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Hi folks,

For a naturally aspirated road course motor with high compression running on 100 octane gas where would you set the overrun ignition timing and fuel cut off ( overrun) ?

How many degrees should one retard for hard cut igntion & fuel for overrev ?

Thanks ,

Adrian

I typically just extrapolate the timing map down into the lower vacuum areas of the table that you can't steady state tune on the dyno. The timing in over run isn't overly critical, particularly if you're using an over run fuel cut strategy. Depending on the engine and the rpm, the over run timing could be in the range of 25-45 degrees BTDC.

I don't personally use ignition retard as part of a rev limit strategy, although it can be used to help reduce engine torque as you come up on the limiter. Understand however that this is not relevant when a hard cut is active since all fuel/ignition is cut. Personally I'd just stick to a fuel cut strategy for your rev limit.