[pbp1]

This is a great post so I thought I would bring it back to the top and add some information that is missing here about Air Temperature and its impact on fuel needs.

There is no need to guess or add "Corrections" for air temperature!

Air Temperature does have a proven, direct, and significant impact on Air Density.

The Ideal Gas Law was formulated way back in 1834. It defines how pressure and temperature changes affect the density of a given volume of air.

Since we measure the fueling of an engine in Air / Fuel ratio (? parts of air to one part of fuel), if the Air becomes cooler, or more dense, or heavier, then the only way to maintain the same Air/Fuel Ratio is to add more fuel.

In a TRUE Speed Density EFI system, the Air Temperature reading plays a part in the equation that is calculating fuel needs behind the scenes.

There is a fuel correction vs Air Temp table in the FAST software just like most any EFI software, but just because you have this table zeroed out, that doesn't mean that the Air Temp is not impacting fueling (This statement is only true if you are running in Speed Density).
That table is there for those who run in Alpha-N mode and wish to build in some manual correction for changes in air temperature. I always run in Speed Density mode and leave this table zeroed out.

This is not some black magic that FAST or any other EFI company invented. It is basic physics and it works as long as the system is set up correctly and you have all the correct basic information in your tune (Cubic Inch, Injector size, Fuel type used, etc.)

An incident happened a few years ago that prompted me to do an experiment to validate how the Air Temperature is used to maintain a constant Air Fuel Ratio while Air Temp is changing.

I have two customers with very similar LT1 SS combinations. Both run my system, Both run Speed Density in Open Loop, Both have tunes that have been extensively calibrated so their actual Air/Fuel ratios run right on target with no O2 correction in all conditions at different tracks without changing their tunes. Both are very FAST, consistent, and dependable.

One of the racers decided to try Icing down his manifold to squeeze a little more ET out of his car. He staged the car and when he let go of the transbrake, it was so lean that it coughed and died. Let it warm back up and all was well. I asked where his Air Temp sensor was located and he said it was out near the entry of the throttle body. That would ordinarily be a fine location for it as that is sampling the air entering the throttle body. The issue here was that the ECU was being lied to. The Air Temp sensor was telling the ECU that 100 degree air was entering the engine when the air going into the intake ports was actually much colder than that. He had increased the density or weight of the air without adding any fuel. More parts of air for the same one part of fuel = a leaner Air/Fuel ratio!

So here is the test we conducted. Took the other car, put the Air Temp Sensor in the intake manifold, Iced it down, made a run, and it picked up big time! We got the car back and looked at a datalog of a previous run with no ice, compared to the run with ice. Here is what we found that was different on the run with ice:
The Air temp was obviously a lot cooler.
The Pulsewidth and #s per hour of fuel delivered was a lot higher.
The Air/Fuel ratio was EXACTLY THE SAME!!!
This is with the O2 correction turned off, so what happened was the Ideal Gas Law was once again proven to be true and the True Speed Density strategy was proven to maintain a constant Air/Fuel ratio as the density (Temperature) of the air changed.

Don't believe any of this, I've got a couple of witnesses who can testify.

Hope this comes across as helpful and informative as I intended it to be.