Yes the friction losses in the ICE are significant - especially when running at low throttle (high vacuum). Look in "experients", there was a post or thread recently where someone measured gallons per hour while idleing at various rpms. gph increase was pretty consistent with rpms increase. So there's a "tax" just to keep the ICE spinning that's related pretty directly to the engine speed.
I confess to reading that site quickly.
Mostly good stuff though!
Anyway, my understanding is, warm air intake = good.
Somewhere I read that optimum combustion air is 60-80 deg. F.
Hotter than that probably gets into the range where air density decreases too much. Colder inhibits combustion to some degree.
Only a calibrated air mixer of some kind can really get an optimum intake air temp. Some guys here had a thread re. building one but the electronics involved got beyond what I could follow.
The rear drive Volvos that my family drives had such an air mixer, but mechanical. One tube pulled from in front of radiator, the other pulled from a shell baffle positioned over the exhaust manifold. A wax-based thermostat controls a damper regulating the hot/cold mixture. Trouble is, the thermostat fails after x number of years with no warning, in the "pull in hot air" position. Result is that the air mass meter fails from being inundated with hot air from the exhaust manifold. So most of these cars now have had the damper removed and run on straight cold air.
My FE has been good this summer, mostly around 31-32. I fear a serious drop when temps get below 60. I could reinstate my original airbox with a new thermostat but I just don't trust it - could fail and kill the amm which is very expensive.
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.
Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.