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jrizing

Rx7 GP RPM Limit Settings

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Hi, 

I'm trying to setup engine protection using RPM against Oil pressure but I'm have trouble setting the limit mode to 'Rotary Only'. The option is available on RPM & MAP but not on GP. Is this done intentionally? 

Screenshot (44).png

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For safety type limiters I would be happy to use the standard ignition cut.  For any sustained limiting at high RPM or high boost it is important to use the rotary mode but I wouldnt have any concern for safety limiters that should rarely intervene.

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My understanding is something like this:

For a rotary there are three separate combustion chambers.  On ported engines especially there is also significant intake port/chamber overlap so that fuel/air charge from one chamber can bleed through to the next one following.  If you only cut fuel but there is still a spark then there can potentially be enough air fuel in the chamber (that had no fuel injected) to allow (lean) combustion.  If only spark is cut then the first cycle after the cut is removed potentially has a partially fueled chamber that could cause a lean combustion cycle.   The safest way to limit them is to first cut fuel, then two rotations later cut spark, then to remove the limit you need to first re-initiate fuel, then two cycles later re-initiate spark.

For a piston engine the fuel is added to the same cycle that the spark is in so it doesnt have this complexity.  I believe the reason to not have spark and fuel cut at the same time in a piston engine is due to possibility of injector and spark timing crossing over or overlapping causing a similar effect where you might have a cycle that ends up getting a partial fuel dose.

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