L98 Spark timing and E38 knock sensitivity

[CV8IIM6]

Hi All,

I recently had my 09 VE SSV L98 A6 on the dyno for a power run and noticed what I suspect may be false knock retard. Vehicle is only ever run on 98 octane and is completely unmodified (aside from a relocated VY IAT sensor). The knock only seems to appear on the dyno and the octane scaler was at 0.00 prior to the dyno runs.





I run what I believe to be a conservative high octane spark map yet still logged 3 degrees of KR during the run. I know timing should be dialed in using MBT on a dyno but I’m looking for some educated opinions before I go down that route.

I thought I should be able to get away with a couple of degrees more timing at WOT? And, I’m thinking about desensitizing the knock sensors by about 10%. Opinions appreciated.

Cheers.

[GMPX]

I would suggest that some tuners at this point would listen to the engine (literally), you are right though, the final timing figure you had doesn't seem over the top.

[CV8IIM6]

I logged a few more WOT runs over the weekend (not on the dyno but still in a responsible manner ) and noticed a similar amount of knock retard.
logging individual cylinders i found some were more prone to knock than others at times but they all seemed to be too sensitive.
I've adjusted sensitivity at key areas of each map by 10% but have not had time yet to log any more data.
Hope i'm on the right track.

I would suggest that some tuners at this point would listen to the engine (literally), you are right though, the final timing figure you had doesn't seem over the top.

I haven't had any experience setting up knock boxes or knock phones but might have to check out a few options. Anyone know of any units that are affordable for the home tuning enthusiast?

[gmh308]

I logged a few more WOT runs over the weekend (not on the dyno but still in a responsible manner ) and noticed a similar amount of knock retard.
logging individual cylinders i found some were more prone to knock than others at times but they all seemed to be too sensitive.
I've adjusted sensitivity at key areas of each map by 10% but have not had time yet to log any more data.
Hope i'm on the right track.

I haven't had any experience setting up knock boxes or knock phones but might have to check out a few options. Anyone know of any units that are affordable for the home tuning enthusiast?

How you travelling with this?

Also, how accurate did you find the ECM engine torque number against the dyno torque measurement?

[Highlander]

Ross is there a way to output the Knock actual raw data on the scantool?

Thanks

[CV8IIM6]

How you travelling with this?

Also, how accurate did you find the ECM engine torque number against the dyno torque measurement?

Hi gmh308,

I've done a lot of 1st and 2nd gear WOT runs and adjusted all the knock tables where necessary by 10% 5% then 2% at a time until knock was no longer evident. I then did a couple of 3rd gear runs and noticed a little bit of KR, I suspect due to the additional load on the engine. At this point I decided the dyno would be a much safer and more efficient place for this kind of activity so things have been on hold ever since.

Hopefully I'll have some dyno time within the next month or so. I think I'll disable the knock sensors and adjust timing to achieve max power/torque. Then re-enable the sensors and trim the knock sensitivity tables as necessary.

I logged torque in Nm and the dyno was set up for ftlb. When I take an average (eg between 70kmh and 170kmh) the engine torque and the dyno torque are very close (within 10ftlb). At peak torque however, the dyno reads nearly 30ftlb lower than calculated engine torque.

Cheers.

[CV8IIM6]

I’ve been doing a lot of data logging lately setting up a MAFless tune and have continued trimming the knock sensitivity tables running total timing as above. I had to increase the value of some of the cells by up to 40% in order to eliminate most or the false KR.

I also managed to get a little more dyno time the other day, I played around with WOT timing and mixtures with interesting results. I had about 3 runs on a mainline dyno (L98 Auto in 4th gear), this is what I found:

I had a bit of a freak run with the stock standard tune. It averaged 12.0 AFR, knocked the whole way through the run resulting in average spark of 18 Deg and still made 219rwkw.

The next run with my tune maintained 12.8 AFR and 20 Deg making 220rwkw. So it seems with similar timing, leaning the mixtures from 12.0 to 12.8 made NO difference.

I then added 2 Degrees which leaned the mixtures to 13 AFR. Audible detonation was evident, timing was pulled and power dropped to about 213wrkw.

At this point I ran out of time.

Next time I’ll try 22-23 Degrees total timing again and aim for 12.5 AFR to see if I can improve on 220rwkw. But, at this stage it appears that my L98 is at its limit on 98 octane fuel with standard intake and exhaust and won’t take much more than 21 Degrees total.

Cheers.

[RetroAus]

We achieved around the same with bone stock VE on Mainline .....

[L31Sleeper]

What is a 2009 L98 (I'm only familiar with the L98 350 in the C4 corvette)

[gmh308]

What is a 2009 L98 (I'm only familiar with the L98 350 in the C4 corvette)

An LS2 6L bottom end with L92 heads and car intake (now superceded to LS3 intake - same/similar head casting as LS3, L76, L99).

Fundamentally the same plant as in G8 Pontiacs.

Out of GM they are L76 - with AFM, L98 - without AFM.

They emerged for MY06.