[RH77]

I have a brief response -- incomplete answer.

From the shop manual on my vehicle, the engine is intended to run richer at intake temperatures below a certain figure (I forget the exact number, let's say 60F). Warm air is needed to satisfy this requirement, especially in Winter.

Beyond that, I've determined with repeated testing that my engine operates most efficiently with IATs at 90-100F. Beyond 120-130F, it starts to dump-in more fuel to compensate for pre-ignition, and fools with the timing. So that temp above the maximum requirement of ambient up to at least ~90F yielded around a 15% increase when I first tested it 2 years ago (the abstract is floating around somewhere -- I think there was a cold-air intake on the car before). FE drops when colder air is introduced, even at ~70F, which is well within the requirements of the sensor/ECU closed-loop management. You may find terms of HAI and WAI (hot and warm air intakes).

How it works -- not exactly certain. A couple years ago I did quite a bit of testing with different temps and found the "sweet spot" for my car. There's still quite a bit of discussion on the topic and the term "pumping losses" can best be explained by someone with more Physics knowledge than I have.

My advice? Experiment yourself with different temps -- and stay as Scientific and consistent as possible. See if you can obtain info on IATs and the vehicle ECU's compensation from a shop manual or enthusiast website. BTW, what kind of vehicle do you have?

Let us know if you test and come to some conclusions.

RH77