IATs VS Ignition advance angle

[jasaircraft]

Hi, 

How should the logic be, the colder the IAT the more or less ignition advance? Although most people say it should need more ign advance, I have yet to hear from someone that has tested it on a dyno to see if it gains torque or stays away from det. 

I was thinking maybe since colder IAT is more dense (as in forcing more air in ...ie turbocharging) we should retard timing as we do on higher load areas on a usual timing map.

 

[Dave Kriedeman]

Hi jasaircraft,

there are all sorts of theories on this and no true hard fast answer as every engine is different as we all have heard 10 000 times.

I personally set up the IAT correction for Ignition timing to advance a couple of degrees for a drop in AIT, and retard for an increase in AIT.

This is a fairly standard approach to this parameter.

For AIR TEMPS around 20 -30 degrees max I use 0 trim, for every 10 degrees increase in air temp I retard 2 degrees.

For every 10 degrees decrease in Air temp I add 1 degree.

These are my start points and then they need to be proven and tested (tuned) on the dyno.

Colder air is more dense , there for you also need to add fuel to make up for the extra air density.

Cooler air (more volume ) plus extra fuel to compensate for the extra air requires more ignition advance to burn the complete mix or as close as possible.

Also cool air charge helps keep the combustion area a little cooler helping with the reduction of hot spots , especially on knife edge combustion chambers etc.

The best way to tune this table like all compensation tables is on a dyno, however with good AFR feed back and Knock control enabled and proper data logging optimising these points can be a little more accurate when there is no dyno available.

Regards

Dave.

[jasaircraft]

Hi Dave, thanks for the answer.... I asked because I just tuned (we never say "finished tuning" lol) a my99 Sti and enabled most features since its a rally car, one of them Antilag system is quite harsh on the turbo and on IATs... I did some datalogging and saw max IATs of around 120 deg celcius...  this tendency to heat air also makes my ECTs increase and be around 100deg celcius... The car didnt heat up but just hovered around those temps while the car raced with the antilag system ON, the Engine temp gauge from the stock gauge cluster remained in the middle.

Now I saw a little bit of knock on the spark plug (I havent yet set up internal knock control with the stock subaru sensor since I havent had the time to experiment)... and Im pretty sure this knock appears on this high stress situations because while tuning I always cheked the plug and did not see this. So Im guessing that probably the ignition timing for high IATs is a bit too much on my comp table. We have to test the car on the track now to see this and also if AFR is within range.