I confirmed this week that the IAT controls timing on my car (someone checked their shop manual). so any gains in temp may be offset by reduced ignition advance. though i don't know the exact relationship between the 2 variables.
last week i also attempted to run a second set of tests at much colder temps, but abandoned it half-way thru. the theory was: WAI benefits will be more pronounced the colder the ambient temp is.
but the ambient temp was slowly rising as i did the first 4 bi-dir runs (about 4F from the first run to when i quit) and this was reflected in the values i was getting in the control set (it could also have been the driveline continuing to warm up to operating temps - even though i had about 1.5 hrs of driving). ambient was around -16C /3F when i started.
cold-weather testing is just too hard. there's too much variability.
so i'll be waiting for spring to do any more scangauge experiments.
my conclusion on WAI: whether it helps depends on the specific vehicle and how it responds to IAT temps. The independent benefit of less dense air on reducing throttling losses is going to be very small as to be essentially undetectable. and in my case that density efficiency gain may have been offset by reduced ignition timing anyway.
Basically my setup is near the header the pipe is the hottest and the more it goes from the header the cooler the pipe gets. It seems to be working, my mpg went up like crazy. At 300 miles it hit the 1/4 mark. Don't forget I have transmission problems and I put those two mods when it was after 200 miles.