| I've discovered a lot of interesting and conflicting arguments on car forums regarding the effects of high humidity on an engine's performance. Since I'll be tracking my car this weekend in a high heat, highly humid environment, I'm curious about whether turbo-charged engines gain an advantage from humidity, or are penalized by it, relative to normally aspirated engines. And, tangential to that, whether I'd be better off using race gas with Ethanol (for its added oxygenation), or without (for its greater specific energy content). Obviously, high heat is gonna' sap the strength of all the engines at the track this weekend. But I'm finding conflicting arguments about the effects of humidity, and -- specifically -- the impact of high humidity (all other variables factored out) on engines with MAFs, turbos and intercoolers. With lots of water vapor in it, the air flowing through the MAF contains less oxygen than air in a dry environment. (Some contend that the air is more "dense" when highly humid. I think it's less dense, if density is defined by oxygen content.) Presumable, the MAF recognizes the difference, so the ECU dials back on fuel and retards timing accordingly. The hot, humid air is also less compressible. So, with wastegates set to open at a pre-determined pressure (say ~16 lbs./inch), there'll be less oxygen in the charged flow running through the intercoolers. The humidity in the ambient air running across the exterior of the intercoolers might offer a bit more cooling than if the ambient air were dry, since its high water vapor content makes it better able to carry away heat. But that difference is probably negligible. Some contend that the humid charge air reduces the likelihood of pre-detonation, because the water vapor makes it cooler. They liken it to the effect of water injection. But, as I understand it, water injection cools the charge air through the cooling effect of evaporation. That doesn't apply to compressed humid air. So, anyway, less power all the way around. I think I understand all that correctly, but any of you engineers (or others more familiar than I am with fluid dynamics) are encouraged to set me straight. But that brings me back to the question: Do our turbos give us an advantage in high humidity environments -- like they do in high altitude -- relative to naturally aspirated engines? In other words, are we less penalized than they are? Or more penalized? Or is there no difference? And, secondly, will my engine be happier with the 100 octane (10% Ethanol) race fuel, or the "pure" race fuel (98-octane, Ethanol free)? The mods in my profile are up-to-date. Thanks for any insights you're able to offer!
 
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