Timing explaination

[odd boy]

Can any one explain how I can change the spark timing effectively?

[joecar]

OB, welcome to the forum... :cheers:

To change spark timing, edit the high-octane spark table B5913.

The PCM runs primarily from this table.

When knock is detected, the PCM slides between B5913 (HO) and B5914 (LO), using a weigthed average between the two, where the "weight" slides down to the LO table as knock persists, and slides back up to the HO table when knock is absent.

What vehicle...?

Cheers,
Joe
:cheers:

[odd boy]

Thanks Joecar,

I am leading a small "GM sport car" group, we are in the stage of building ourselves and I am asigned to be the programmer.

What is not clear to me is that: do I have to change the whole table? or I modify a certain portion of the table? If yes what portion I should change, to what values, under what basis?

Sorry for asking a lot, but I am in a learning stage.

[hquick]

Hey Odd boy....
You know...I'm new to this as well and I'm enjoying reading the replies to your questions (still learning).
One thing I found useful in trying to learn how to use this Pandora's Box of vehicle tuning is...go through the tune from start to finish and run a search on every single parrameter and then read through all the threads you can find on those searches.
It'll answer alot of questions (and maybe raise a couple more). I'v learned ALOT through this method.

[odd boy]

thanks a lot for the advice

[TAQuickness]

You can change timing at given load points (each cell on the table is a load point). It's quite helpful to enable the run-away highlighting feature and watch the tune tool while scanning a vehicle in action. This paints a nice visual of the areas you may want to adjust.

[odd boy]

how could I know if I need to advance the spark or retard it? Shall I depend on the associated knock sensor or I should get a separate one? how could I determine if the first knock is the limit?

[TAQuickness]

Best thing is to get on a dyno and monitor the effects of your spark changes on HP and TQ. Advance until the engine produces no more HP/TQ, then back off 1 or 2 degrees for safety.

I would not recommend advancing to the knock limit then backing off. For me, the potential for engine damage is to high to risk the investment.

[joecar]

I agree, set timing on the dyno, but be sure to get the target AFR dialed in (AutoVE and commanded fuel and PE tables).