I posted this question in the Rotary Performance section as well, thought maybe the PFC guys may have a bit of insight as well...

I've noticed I'm registering higher knock readings on my PFC when I lift off the gas than on. I'll make a drag pass, no real readings to speak of, but let off the gas and I'll sometimes, but not always register a number in the 30-65 range, even greater on occasion. I did recently change my trailing maps, not my leading, to eliminate what many think is too much split (upwards of 17 degrees), but the changes weren't drastic. Again, my leading timing was unchanged and I never registered numbers as high before. The only other change I have made is the addition of premix (2-stroke synthetic) in the gas, fairly small ratio, and the adjustment of trailing timing.

I have two theories; one, the premix lowers octane a bit (but then I'd get knock readings on acceleration, no?), and the second is that the trailing ignition times cause more "severe" backfires as I lift off the gas, setting off the knock sensor. You know...the trail of burbles as you decelerate of the gas and the occasional flame shooting spectacle? I'm not talking massive explosions in the tailpipe, the backfires are nothing large or unusual for a rotary.

Any theories or facts on why the readings are higher or what causes them on deceleration? Thanks in advance.
Michel

 

It is easy to make a quick temp IGT across the board change and see if it really affects the of throttle noise level.

Otherwise it might be drivetrain noise.

 

I'll have to try that. I just installed a new 40gig hard drive into my laptop so I'm in the process of setting everything up again for datalog. Just haven't gotten around to it.
Michel