Buglerank62 said:
Question, if I use higher octane premium rather than regular does that help if I fill up with E85?
First, understand what an octane number
is.
A hundred years ago, automobile manufacturers decided to engineer cars to go faster, so they increased the compression ratio in their gasoline engines. But when they did so, they found that the fuel/air mixture had a tendency to randomly prematurely ignite before the spark plug fired. This made an annoying "knocking" sound and damaged the engine. So the industry did a bunch of research to see if something could be added to the fuel to reduce the problem. This required having a way to quantify a fuel's knock resistance.
Early on, it was found that 2,2,4-trimethylpentane (popularly known as iso-octane) had a low knocking tendency, while heptane knocked a lot. So a man named Graham Edgar devised a rating scale that scored heptane as 0 and iso-octane as 100, and this "octane number" became the gold standard of measuring knock resistance. Real-world gasoline is a mixture of different chemicals and doesn't necessarily contain a lot of iso-octane, but its anti-knocking performance is
compared to iso-octane.
Various octane-boosting chemicals have been used. Tetraethyl lead was popular for about 50 years, but horrible for air quality (and giving children brain damage from lead poisoning), so it was banned (hence all road vehicle gasoline today being "unleaded", but leaded
aviation gasoline is still a thing for some reason). Methyl tert-butyl ether (MTBE) replaced it for a while, but it pollutes groundwater and was suspected of causing cancer, so it too was phased out.
Today, the most common octane booster is ethanol, which has the advantage of being relatively cheap. Its main disadvantage is that ethanol has about 1/3 less energy per gallon than the rest of the gasoline, hence the complain that ethanol decreases gas mileage. It also has high enthalpy of vaporization, which means that it doesn't ignite as well during cold weather (a problem which some countries work around by using lower-ethanol blends in winter). Ethanol can also corrode fuel lines, gaskets, or seals in older vehicles that weren't designed for ethanol-blend fuel.
But that's a digression. My main point here is that octane number
ONLY measures a gasoline blend's resistance to engine knocking. It does
NOT measure energy content, mileage, shelf life, amount of residue deposits, or any other relevant criterion for evaluating gasoline.
So, if your car has a low-compression engine and experiences no knocking with 87 octane gasoline, then using 93 octane will...also produce no engine knocking, but you'll pay more for it.
