Quote:
Originally Posted by Chuck33079
My wild-*** guess is that the cooler charge allows the ecu to use less fuel as a safety margin. At the end of the day, it's probably all statistical noise and the gains all come from the tune leaning things out.
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If one of the factors that affects target AFR is IAT's then that would certainly be true.
I think it gets confusing in part because power and MPG are kind of unrelated issues when you get down to it.
You could coast downhill consuming very little fuel and engine power, and improve MPG, or you could destroy a new set of tires with a smoky burn out, consume tons of fuel and produce lots of power (or, well, torque more precisely), go nowhere, and have terrible MPG.
Fuel consumption comes into play on the basis of fuel consumed to make so much torque over a period of time, but it doesn't necessarily translate into distance traveled.
That's why gearing and drag (either in terms of tire inflation, weight, or the ability to deflect wind) all wind up being such surprisingly important factors in MPG (those little plastic wind deflectors in front of the front tires come to mind...).
That's also why city MPG is always lower than highway MPG; taking off from a dead stop (i.e., stop and go driving) requires more energy than rolling along with the help of inertia.
I don't know about heat losses related to airflow, but losses as heat matter definitely in some aspects of MPG. A fluid coupling trans, for example, will lose power in the form of heat, and therefore have a poorer MPG than a solid connection to the driveshaft operating under the same conditions (although gearing and time spent in a given gear will affect MPG too).