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Rotary fuel tuning - over run areas

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Hi all,

In one of the webinars (cant remember which one) Andre mentions that it is worthwhile tuning the fuel in the overrun area even if you intend on running over run fuel cut. As this is a bit hard to achieve on a dyno, I took the car for a drive down a hill and let the ECU software do an "auto" tune in these areas using closed loop.

The problem I found is that the VE numbers in the overrun area (-24inHg) are very high at around 130-140, especially when compared to the row below (-18inHg) which are around 65-75.

I am obviously using VE tuning, my AFRs are set, injector data is correct, etc. and ORFC is switched off. The VE in the rest of the vacuum areas looks normal, its only in the over run area which doesn't look right.

I noticed in the Rotary Ignition Tuning webinar that the timing in the over run area is significantly lower than the rest of the vacuum table. But I'm also thinking that due to the slower flame that I should increase my ignition advance even further in these areas.

Engine is a 13B-REW with a very mild port.

Hi Rob, you may find that auto tune is a little bit hit and miss when you're completely off the throttle and it sound like this is what may be causing your issues. For autotune to work effectively you need to be pretty close to the centre of the cell being tuned and you also need to be able to hold in that cell constantly for a few seconds generally to get a good result. You may also find that the engine doesn't run perfectly on over run and this can give you unreliable lambda readings that will throw the tuning off. Personally I'd try extrapolating your map into the vacuum areas and then pick a few key cells that you can steady state tune at the high rpm, high vacuum areas. try and get down as close as you can to closed throttle. I'd then interpolate your results between these key cells and perform a little manual smoothing to get a map that makes sense. That being said, given the fact there's no load on the engine you're not in danger of causing damage so you don't need to over think things too much.

Thanks Andre. I'll give it a try and see how it goes.

I don't rely on autotune for transient or overrun conditions of any of my rotary builds. I sometimes will use it as a diagnostics tool but I'm generally able to dial it in far better and far faster myself.