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.
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.