/"\/oo\/"\;18363389 said:
if anyone (Chevrolet, Toyota, BMW, whoever) had a way to get an increase in fuel efficiency to the magnitude that adam044 is claiming, they would advertise it everywhere and make consumers knew that the higher cost of fuel didn't matter because they'd be using so much less of it.
After that are cars that only recommend premium for best performance, which I think we agree is pretty self explanatory. The difference between regular and premium in these cars is fairly marginal and using regular will never hurt anything.
I think it's a bit of a misnomer how gas stations use the word premium for high octane gas. Perhaps it stems from back in the day when luxury imports were the only cars on the market with high compression engines, thus it was seen as a premium gas.
It really only makes sense to use high octane if your engine has a high enough compression ratio that premature detonation becomes a problem. Put it this way, if you're getting 200+hp out of a 4 cylinder engine, it probably has a high compression ratio.
In cheap cars that's a common restraint though, because if your value car requires higher octane gas it's going to get slammed in the total cost of ownership figure (even if it's really not that much money), especially because cheap cars are usually sold as budget conscious cars.
Thing is, if your car's manual says use 87 octane, use it. If it says use 89 octane, use that. If it says 91 octane, use that. Unless you modify the engine, or they release a TSB saying they screwed up and it'd actually run better on the higher octane, you're just wasting money on higher octane gas. As said before, the car's computer will react accordingly, and may make more power (unlikely) or make less power (probably more likely) to deal with premature detonation or such things.
Now if you decide to mod your car's firmware and tune it to use a higher octane gas, that's a different story.
Now for my related thoughts: It's not unusual for turbos to exist in the higher end ford/chevy compacts, driving the car towards higher octane fuel. Still, it'd be weird if a car company made the cheap mass market version of their car require high octane fuel, a lot of people would probably force the cheap stuff into it anyway.