Of course things like coolant temp, oil temp and intake air temperature affect the optimal spark advance angle for the engine.

To keep this simple, let me just talk about intake air temperature correction to the spark map on a naturally aspirated engine...

For an NA engine lets just assume intake air temperature equals ambient air temperature.
I can see that when one builds the basic spark map, then that is the optimum spark map for the ambient air temperature that day.

It is also clear that in general, you can run a more advance when the ambient air temp is cooler, but must run less advance when it is warmer. This is typically handled by a correction factor that adds or subtracts degrees of advance depending on the air temperature. So if you tuned your base spark map at 23*C air temps, you would not want the correction table to alter spark advance at this temperature at all. When the temp goes up to 30*C, you would subtract 2* of advance (for example). When it drops down to 15*C you might be able to add 2* or 3* of advance.

My question is, how exactly do you know how much to add or subtract? I had a few theories on how one might determine this:

1) Try to do a tune session on a cold day, and one on a hot day, then extrapolate the difference into you correction table.
2) you know the best torque values at 23*C so you just "play it safe" everywhere but at this point (this would result in production of less and less potential power of the motor the farther you get from 23*C)
3) There are some math equations that will help you develop the temperature correction table.
4) You just emulate what others have done.

How do you guys handle this exactly?

Thanks,
Max

P.S. Are you guys doing humidity correction?

 

PM cewrx7r1 (Chuck Westbrook). there has been a large discussion about this somewhat recently on the Yahoo PFC group he runs

 

There is only one "IGN vs Air Temp" table with 3 rows (temp settings) under Settings 3. Its default use is to retard timing as air temps gets high to prevent detonation on boost with an overheating IC. It could be used for optimum timing vs air temp by rearranging the table. But being only 3 rows reduces liniarity.

You can not run more timing with colder air. With colder air an engine will make more power at the same boost level due to a denser air charge and more fuel.
In summer at the same boost, air will be less dense and power will be down.
Less boost allows more timing advance than more boost. Tbhus it is safer to tune for power in winter than in summer.

Your idea of timing vs air temp only applies when the air temps get very high and pass the safe zone.