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I'm so fucking confused, man. I'm a tech guy. I've spent my whole life getting good with computers, I know very little about cars, and I just can't keep up. I've heard that yeah ethanol is bad but put in your tank what the manual says because if your engine isn't designed for "high-octane" fuel (???) you'll damage your car with the pure stuff? But I know how ethanol dries out rubber, which I'm quite sure is what my fuel lines are made of, but my manual says to use 85. So should I be using 87 and avoiding 85? Or...?
I just want an electric car. "Plug it in", I get.
I think you're confusing e85 with 85 octane gas
E85 is 85% ethanol, 15% gas (and e15 is the other way around)
Octane rating is a measure of how much you can compress a fuel before it ignites by itself. Higher octane gas is more resistant to that. (And e85 actually has a pretty high octane rating, usually somewhere north of 100. Regular gas often contains up to 10% ethanol, in part because it boosts the octane rating)
To expand on that a bit, if you compress gas enough, at a certain point it just catches fire on its own. This is actually a big part of how diesel engines work. Diesel is actually pretty hard to ignite, in some cases you can even put out small fires by pouring diesel on it (don't try this at home) so they rely on getting high enough compression in order to work.
Gasoline is a lot more flammable though, you don't really need to compress it at all for it to burn. Sure, ideally you probably want a certain compression ratio because something something stoichiometry but gas is more forgiving in that regard. As long as your air-fuel mixture is about right, it's gonna burn when your spark plug goes off.
In fact, gas is maybe a little too forgiving, if your octane rating is too low and your engine compression is too high (mostly a problem with higher-performance engines) that gas can just kind of go off too early before the spark plug goes off, which causes "engine knock" which will cause damage.
But the other way around, high octane in a lower compression engine, basically does nothing spectacular. It still goes boom when the spark plug goes off and not until then.
Just to clarify, the three numbers at the pump (87, 91, 93 I think?) are the octane rating which the other comments explained. The ethanol content is the sticker that says "may contain up to 10% ethanol". This post is about increasing that percentage of ethanol in regular gas, which as other comments explained mostly just makes the gas less efficient.
E85 is 85% ethanol and 15% gas, basically the reverse of regular gas.
Fun fact, if you go somewhere with high elevation your going to see lower octane ratings. Colorado for example. https://www.slashgear.com/1825420/colorado-85-octane-gas-reason-substitute-87/
That is, and I say this completely sincerely, both the coolest and most fun fact I've learned all week. Thanks for sharing!
Here's my laymen's understanding:
Higher octane fuel (85 vs 87 vs 89 etc) prevents premature detonation in the engine. Detonation needs to happen at a very specific timing in each cylinder (IFF the sparkplug is sparking), but if the fuel is too "eager" to explode it could detonate early just from the heat of the engine, which eventually breaks shit. Octane makes your fuel just a little less explosive, so higher octane rating can compensate for engines more prone to premature detonation (basically most engines that run hotter, high revving, with turbos, some modded engines etc).
Running too high octane doesn't hurt or help you if you weren't detonating prematurely before. You'd just be throwing your money away running higher than recommended by the manufacturer (ok it can help clean the engine of carbon deposits similar to how a can of seafoam would, but really you'd be better off using the seafoam, and like seafoam it'd be overkill to do it all the time).
Now using too low an octane rating, it depends. In older cars, you'll just get premature detonation and it'll blow shit up, just don't do it. Most modern cars though are smart enough to adjust their timing to compensate for low octane fuel and avoid damage (check your manual to make sure though). However, you'll be getting worse performance, worse efficiency, worse emissions, basically your car will drive worse and you won't actually be saving money with your reduced milage. Unless it's an emergency and you have no choice, get the recommended.
Octane is basically irrelevant to the issue of ethanol. The relevant issue is that gasoline (ethanol-free) has a specific energy of 47.3 MJ/kg, while ethanol has a specific energy of 29.7 MJ/kg. You need 1.6 gallons of ethanol to get the same energy as a gallon of gasoline.
I don't think there is a regular 85 octane lowest in Nebraska is 87 octane. E85 is the ethanol version but your vehicle has to be able to use it.
Some 87 here can have small amounts of ethanol if it says so at the pump and that can be used in normal vehicles. Older cars pre2000 don't run well with it and some with carburators can get vapor lock
Okay so to quickly summarise: the octane number defines just how explosive the fuel is under compression. 100 means it's the equivalent of a 100% iso-octane mixture.
The more explosive the fuel is, the sooner it detonates as the cylinder compresses it. If it detonates too soon, at too low a compression, that's when your engine starts to knock. By adding ethanol you're increasing the pressure needed for detonation, ensuring that the ignition system ignites the fuel at the appropriate time, thus improve the engine's longevity.