[RedDevil]

On my Insight the effect of warm air actually reduces FE when above say 110F.
To be precise; the hotter the engine gets, the cooler the intake air should be.
Sounds logical, no?

I ran it with LGB and no snorkel (which sucks cold air from the top grille to the intake behind the rad; so without it it takes radiator-heated air) and it went up as high as 125F even in very moderate driving. Sure FE dropped.

But the Insight II has EGR; up to 15% of the air it takes can be exhaust gas to improve clean burn and raise intake pressure on partial load, increasing efficiency. It also raises actual intake temp considerably.
Cars with no EGR can do well on higher intake temp. But even then the engine temp will play a part in the equasion.

I am planning a regulated WAI for my Insight. I'd love to be able to operate it while driving and find out what temp is best in what condition, and program it to reproduce those settings whenever needed.
Or even better: find out that someone has done that already and pick the fruit without having to plant the seed. I'm vigorously lazy, if needed.