Optimal Timing vs High Octane tables

[efizjb]

Hey guys, excuse my ignorance and being new to this, but how do you know (like say in a data log) when the ECM/PCM is going off of the optimal timing table as oppossed to the high octane table, more importanly when at WOT, or does it default to one or the other at WOT/OL?

[BlackGMC]

I think the computer only uses the Optimal Timing table in calculations... From my understanding the computer always tries to use the High octane table until it reaches a certain amount of knock in a given time period then it reverts to the low octane table...

[cmitchell17]

Yeah I guess the optimal timing table is used for torque calculations. So im guessing that the farther off you are in timing from the optimal table the certain amount of torque you make.

But at part throttle no PE optimal timing seems to make no diffrence.

But there is a PID you can monitor that gives you a percentage of how much High or low timing table its using.

[joecar]

GM.ASPARK

This is the percentage of timing from the HO table.

Timing = (ASPARK * HO_table) + ((100 - ASPARK) * LO_table)

100% = running from HO table
0% = running from LO table

KR present causes ASPARK to tend toward 0%.
KR absent causes ASPARK too tend toward 100%.

Regardless of WOT or OL/CL.

[efizjb]

Thanks guys. Both my tables (optimal and HO) were low in the WOT areas of the tables, but wanted to be sure when it referred to the optimal table as opposed to the HO....

[joecar]

The Optimal Timing table is used for torque calculations only, as BGMC and CM17 said above.

For your actual timing, the PCM will use a blend of the HO and LO tables depending on ASPARK (which is influenced by KR) and any modifier tables.