Spark tuning is an art that many people don’t know how to approach properly. It is one of the best ways after fueling to either add or loose Big power from your car.
As a good rule of thumb, for every 1* of spark timing added/subtracted from the tune, it is worth approximately 3-5whp
Now I know most of you are thinking if that is the case, then add as much spark timing as possible until you get Knock, well, there is a such thing as having too much spark without getting knock. In general for the GM 3800 cars, we like between 28-30* of timing at Wide Open Throttle. (WOT)
It is also important to note at this time that our cars, and many others have 2 timing tables, High octane and low octane. For the GM 3800 vehicles the way these tables work is quite simple, your car will attempt to run the high octane table, so long as you are not seeing any knock. Once your car starts to see knock, it will begin to pull timing and will revert to the low octane table. Under no circumstances should you copy your high octane table over into your low octane table…ever. If you were to ever get a bad batch of gas and your car cannot pull enough timing, you’ll damage the motor. As a result, I generally copy my high octane table into my low octane table and subtract 3-4 degrees of timing from the entire table.
If there is one thing I hate when spark tuning a vehicle, it is when a pcm starts adding/pulling timing when I haven’t told it to do so. For this reason I go into all extra spark tables outside of the high/low octane tables and zero them out.
For those of you with the 3800 I am talking about the Spark Correction base, IAT spark base, and ECT spark base tables.
Since you zero’d out all the other tables you have removed any variables that might change what you are commanding for spark. All changes you make will be through the high/low octane spark tables.
For my personal Tune I do not have much more than about 30* maximum timing at cruise. However I am sitting between 26-30* smoothed out across my cruise cells.
I run approximately 30* through all my full throttle cells.
The best way I like to tune spark timing for wide open throttle timing is to go out and data log a few runs. Go wide open throttle until you fill up the spark cells (for the 3800 it is the 0.80 and 0.92 cells). Begin adding timing by 1-2 degrees at a time until you either hit about 29-30* or some knock. If you recieve some knock in just one cell, back off the timing for that one cell only.
This way if at full throttle and 5200rpm you are seeing knock, you are not pulling timing at 5600rpm when you can still have a little bit more spark and making power.