Question about "Optimal Timing Table"

[67SS509]

Does this table have any effect on the final timing that is commanded with a LS1B PCM? When logging I have all of a sudden started seeing more timing in the log then is being commanded in the spark table at WOT (as much as 8-10 degrees more). I don't see any tables that would add this much timing and the only table I can find with timing numbers that big is the Optimal Timing Table B5919. Everything I see like the ECT and IAT tables usually subtract timing. This just started recently.

[67SS509]

Here is a log showing the added timing in question. At frame 1093, RPM 5573 and Grams/sec .65 log is showing 29.5 degrees of timing. At same axis on the Hi-octane table the commanded timing is 17.4. Where is the extra 12.1 degrees coming from?

[joecar]

The Optimal Timing table is believed to be used by the PCM for purpose of calculating and comparing various things... I don't know that it is ever commanded, but I don't know enough about it.

[67SS509]

Thanks joecar! In the log I posted above, do you have a guess where the extra timing is coming from?

[joecar]

Good question... post your tune file also.

[ND2RACE]

Looking at your log, your IAT is only 59 degrees so I'd be looking at your adder tables, especially any to do with intake air temp. Without seeing your tune it's hard to say, but it's getting added somewhere. As for the Optimal timing table, I once was curious about it and copied my finished high octane table into it, never noticed a difference, but figured that it was "optimal". To clear though I don't recommend doing it as I'm not sure exactly what it does.

[67SS509]

Here is the tune. It's a customer's 2001 Chevy truck stock with a Hypertech programmer installed. Went back a few months and looked at some logs and they all showed within a few degrees of the commanded timing. The last 3 cars I logged showed this kind of error. The only difference is I recently updated.

[67SS509]

Guess I found the culprit. The extra timing is coming from B5908 Fuel Mixture Spark Correction. The Hypertech is not leaning the fuel out at WOT like I normally do when tuning with EFIlive. Learn something new everyday!

[joecar]

Good find, that explains it.

[ecir45]

Thanks for bringing this up, had the same problem. Looks like we can just zero that whole table out.

[67SS509]

That's correct but you will need the timing tables from a tune that has the tables zeroed out.

Thanks for bringing this up, had the same problem. Looks like we can just zero that whole table out.

[ecir45]

Thanks for the tip. What tune did you use to swap all the timing tables?

[Mikz86ta]

Same question as above

[Tre-Cool]

if your retuning the spark maps anyway then there is no need for the eq factor table imo. They did the same thing on the 1.6t e83b cruze tune. got rid of all the factory mess.

[67SS509]

Some operating systems in the same year model use the spark correction for fuel mixture and some don't. The timing is more controllable without the corrections so I just zero it out and then use the spark table from an operating system that has it already zeroed out before I start tuning.