Need help understanding Cobb access port

burnsbp said:

okay guys so I am stage two now running an ots tune from Cobb. I've been using my access port to view some specs of my car. the two things on here that I need help understanding is Knock Ret(Knock) and Ign. Delta cont. knock
Ive been seeing numbers from the knock ret jump to a -3.00 only when wot. that value only shows on some of the pulls I do and not all of the time. the ign cont knock has always stayed the same and I've never seen those numbers move. Im a bit off a noob and don't fully understand what this stuff means, heres a picture of the ap and what I'm reading(picture doesn't show any readings of knock but top right gauge is where I've seen the number -3.00 appear gauge below that has never shown anything)

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thatspsychotic said:

Since you asked for understanding and not just "is this ok", I'll give it a shot.

What you're looking at for Knock Ret is the amount of spark ignition retard that is applied when the ECU detects a knock event. Tuners commonly set the timing a little aggressively and let the ECU apply the -3 degree timing correction when needed. Like you observed, this only really applies at WOT, although it is possible to get light load knocking, tuners generally don't push part load ignition advance far enough to get to that point.

Knock is effectively unstable combustion, where the combustion conditions are marginal enough so that if the spark plug fires too soon, remote pockets of air/fuel violently ignite before the main flame front reaches them, which results in cylinder overpressure that in bad cases can be heard as an audible knock or ping. The timing correction you observe delays the firing of the spark plug so that combustion process begins later, avoiding the unstable combustion event. Up to the point of unstable combustion, increasing spark advance increases combustion efficiency leading to higher power output, so the game tuners play is to advance the ignition enough to make a lot of power, but not so much as to get too close to knocking a lot.

Lots of things affect knock threshold, mostly fuel quality, temperature, etc. A harder knock event would pull a lot more timing out, enough to feel a power reduction and that would indicate a potential problem or a poor tune.

As for the other number that hasn't moved, I don't know for sure, but if I had to guess, it could be something like long-term ignition timing correction factor. The ECU will learn the knock threshold over time (probably under circumstances where more than 3 degrees of timing need to be pulled), and apply an ignition timing retard offset to the base ignition map. The fact that this hasn't moved is probably a good thing, and your car is comfortable with the ignition timing in the tune.

Make sense?

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