I was reviewing my datalogs from a great day at Mosport - supposedly the "fastest" track in North America. I noticed that timing was being pulled in certain places and when I looked at all the parameters I could see a pattern: about half second after I let off the throttle (either completely or partially) there would be a reading in all 6 sensor points (I believe there are really only 2 sensors) lasting about 0.2 seconds. This would occur even if I was on part throttle and then let off the throttle. Long story short, it seems to coincide with the awesome burbling noises from my catless AWE exhaust and I think that's what is triggering the knock sensor readings. On other parts of the datalog when I am absolutely beating on the car there is no knock activity or very little anyway (much less with racegas than with pumpgas, I added 3/4 tank of 98octane racegas when my tank was down to 1/4 of the 94 octane I usually use). Any thoughts/opinions?

 

Very interesting theory.

 

Knock sensors don't usually get fooled very easily. The feedback system is only listening at a very narrow frequency range - and a very narrow slice of time for each cylinder.

 

yeah I know. I thought that it was strange. I figured it must be "real" knocking until I saw that it was doing it consistently even with part-throttle acceleration followed by deceleration. Half second later there it is in the log. It coincides with the burbling so I just figured it was related. It's not often there is identical signal on all 6 of the channels.


I almost preferred the blissful ignorance of not having such detailed datalogging available via Cobb AP. Nah, I like knowing, lol.

 

Knock sensors do not pick up exhaust noise. If they did, 2step launch would not work.

 

You guys are probably right. On second look at the logs it now seems evident that it's when I get back ON the throttle that it just briefly pulls timing (for 0.2s). For example, if I have it floored in third, lift off to shift into fourth, and floor it again it would pull timing in all channels for a brief period.