Timing - Why would GM allow huge KR in all stock C6?

[Amric]

I was lucky enough to run several scans of my 2009 C6 before ever touching the motor or tune. I noticed that scan after scan there was what I would consider large amounts of KR (3+ degrees). Now that I have added headers, catless x-pipe, CAI, and large cam (231/243 .617/.624 115+3), I have been street tuning it.

Each day, I record a maximum (not average) KR of less that 1 degree in a few cells at light loads only. Most cells read 0. I had the policy of no matter how small the KR, I would reduce timing in that cell. Day after day, I find myself reducing about 1/2 degree of timing from cells around my highway cruise RPM/MAP. The next day, I read the same KR in that cell as before I pulled timing. I seem to get no more or no less KR from day to day, and pulling timing seems to do nothing.

It is not something rattling, as when reviewing the scan, the KR is very rare and not repeating in any way.

So I have come to be concerned about the 0.5 or less degree of KR at light loads only, that I have been seeing until I went back and looked at my all stock motor and tune scans. For some reason, GM allowed for crazy amounts of KR (3+ degrees). Why would they allow this much KR in an all stock C6 when I am sweating over getting rid of that last little 0.5 KR?

I have posted a standard all stock scan, and a very typical current scan for your review.

[Atomic]

Thats why they installed knock sensors and use multiple spark tables.

If you are getting random .5 degree spark knock it is probably false knock.

[LSX378]

Are you running factory burst knock settings?

[Amric]

I have tried both the factory burst knock, and slightly reduced burst knock. Both ways seems to result in the same KR. In fact I was a little suprised that after going from the reduced burst knock to stock burst knock, if anything, I saw a slightly higher rather than the expected lower KR.

[LSX378]

I have tried both the factory burst knock, and slightly reduced burst knock. Both ways seems to result in the same KR. In fact I was a little suprised that after going from the reduced burst knock to stock burst knock, if anything, I saw a slightly higher rather than the expected lower KR.

Try it with zero burst knock. Zero out the "Burst Knock Retard" "Base vs CylAirDelta". You have probably been changing this table anyway.

If you zero it out you will know whether the knock you are logging is from the knock sensors, or simply predictive from the Cyl Air Delta as you operate the throttle.

Then if it is burst knock, you know where you are, and if it is knock sensor knock, you can start backing off the right timing cells until it goes away.

Or just let the knock sensors do their thing.

You running 93?

[Amric]

92 most of the time. 93 when I can find it. In the cl8 scan I am logging burst knock and KR both. Back when I did the stock scans, I was only capturing KR.

[mattgallan]

That Cl8 scan is really clean, you have nothing to worry about.

[DSteck]

You can compare burst knock retard to actual knock retard without having to zero out the burst knock. I can't remember which PIDs to show off the top of my head, but that's what I do (although I halved my burst knock settings).