Gasoline Octanes to Use

You're confused about the purpose of higher octane. The higher octane level makes the fuel harder to ignite. That prevents preignition and allows the engine to be tuned for higher horsepower. It does not provide or cause higher horsepower and it has nothing to do with keeping the engine clean.

Most fuels today have some ethonal added which is alcohol. Alcohol is a very good cleaner in itself. In fact, using alcohol in older cars can cause problems because it cleans the fuel system so well that all that gunk collects in the filter and plugs it.

GM has their own injector problems that no amount of cleaning is going to help. Chrysler is one of the few manufacturers that has almost no injector trouble at all. Ford falls somewhere in the middle of those two extremes. Octane ratings won't have any affect on how long injectors last. Unless the manufacturer specifies differently, stick with the less expensive 87 octane. If you hear any pinging under light acceleration, switch to the next higher octane. Understand too that GM uses knock sensors on most of their engines to reduce that pinging. When pinging is detected, the Engine Computer retards ignition timing which reduces power and fuel mileage. You may not ever know that is happening but your fuel mileage will suffer. If you find the mileage improves with a higher octane fuel, it is not because there are more BTUs in the fuel; it is because it is not necessary to retard ignition timing. The correct octane for each vehicle should be listed in the owner's manual. Don't waste your money on anything higher than called for.

Also, thanks to that Engine Computer covering up any noticeable pinging, it may be necessary to drive with a scanner connected that can read live data. It will show how many degrees of timing advance are being requested. If there is no difference between the different octane fuels, the higher octane is not needed.