I decided I would put together a spreadsheet to play a little what-if game with AITs & A/F ratios. After tuning my car to 30 degC (indicated by the AIT, steady state intake temperature), I would notice that my A/F ratios would change a little depending on the AITs. I am using the stock Mazda tables & AIT sensor.

I'm attaching a JPEG picture that was created from my spreadsheet showing 6 A/F ratio VS intake temperature. The first three are based on the table values from Mazda, Kevin, and cewrx7r1 (Chuck); these values are written in Chuck's notes. The 2nd three (indicated by the dots) are "heat soak" curves, where the A/F ratio is different because the air density is actually higher than the indicated temperature. I wonder how many people blew motors up after beating on a heat soaked car? I know my A/F ratios were around 11.3-11.5 after driving off with a little boost on a hot motor (and this is because the air temps would stabilize to 35 or so degC, so if you look at the graph this is right about where the A/F is on the "Mazda Heat Soak" curve).

I assumed a heat soak temp of 60 degC, since that's what I see pretty often after stopping the car for a short trip into a store, to get gas, etc. I didn't include any corrections due to water or fuel temperature, this only uses the information from the INJ-AIT correction tables, and the AIT temperature & the A/F ratio the car was tuned to.

The most obvious thing about this is that if you use Mazda's tables, the A/F ratios go lean in colder temps (winter) and richer in hotter temps (summer). Chuck's tables provide an even A/F for the basic operating AIT range, while going richer in warmer temps and colder temps. Kevin's goes richer when it's warmer and stays even to as cold as it gets

So for me, since I tuned the car to cold air (cold for me is AITs around 30 degC), I'll be running richer, around 10.5:1, in summer (AITs around 50-60 C). This is why you should tune your car in cold weather!

I can't directly attach the spreadsheet, but if anyone wants it I can upload it to my website do you can download it. Any questions or corrections are welcome

EDIT: I used the pressure at sea level to calculate air density. I didn't include any corrections for humidity, but it would effectively increase the air density and contribute to a leaner running motor.

 

Actually, what is technically correct is that an increase in humidity leads to a decrease in air density... read here for details:

http://wahiduddin.net/calc/density_altitude.htm

When absolute pressure is measured, it contains components due to both dry air and water vapor. In my calcs, I assumed that the total pressure is due only to dry air, I have to check my dyno conditions to see what the humidity was on the day of tuning... That may explain my car running leaner out where I live (desert-like) as opposed to down in San Diego, by the beach with increased humidity. I'll add that feature to the spreadsheet too at some point in the future.

 

Even with a modified table you can still blow the engine by boosting on a heat soaked engine. This also can happen with the air temp sensor being placed in the IC outlet or TB elbow (these are better than the stock position under the UIM).

A smart owner knows to wait until the engine is full warmed up from cold, or cooled down from parking heat soak; befor getting on full boost.