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Why does ECU advance timing suddenly when getting out of WOT?

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Hi, in the attached image of a log file the timing is advanced another 10 degrees when moving from open throttle to no throttle. I am just looking to understand the thought process behind it.

Attached Files

What ECU?

Please do post your calibration file.

Can you post a screenshot of the spark maps?

Flame speed is slower at lower charge pressure. Looks pretty normal.

Hi, DynoDom, it is Nissan ECU with UpRev re-flash software. Raymond, by spark maps do you mean Ignition Timing?

Ok, So Flame from propagates through the gas in the cylinder slower when it has less air (lower pressure after being compressed). Thanks, I didn't know that. So is that part of why a higher compression ratio is able to extract more power? Higher Compression can have the timing advanced less than lower compression but still get the peak pressure at a similar point in the cycle.

Hey Rob, check out this particular module in the EFI Tuning Fundamentals Course. It will explain everything nicely:

https://www.hpacademy.com/dashboard/courses/efi-tuning-fundamentals/the-tuning-process-tuning-ignition

Higher CR usually allows both less advance (and hence less negative pumping/friction) and a higher conversion rate of heat to mechanical energy in the expansion stroke itself. That is why you have miller cycle stuff, less compression on the way in but higher expansion ratio on power stroke.

The closed throttle and high vacuum in the manifold is associated with the slower burn.