That would be a complete waste of money and could be potentially damaging to the engine. Read on.
People have long held the mistaken belief that a higher OCTANE number means more POWER or that it's CLEANER or just BETTER for the engine. It's just not true. Just today I heard yet another guy talking on my Ham radio about how every once in a while he runs a tank of premium through his car because he thinks it cleans out or restores his engine or that he is somehow rewarding it for good behavior. You will receive no benefit from the higher octane fuel UNLESS your engine is designed to take advantage of the difference. Higher octane fuel does NOT mean more BTUs of energy. Jet fuel, which has the highest number of carbon atoms in the chain has only slightly more BTUs than hexane (base gasoline), which is the what octane is blended with to come up with the different octane ratings. It's all about how much compression the fuel can withstand before it ignites by itself (before the spark plug fires) which is what you obviously don't want to happen. Higher compression engines, and engines with a longer power stroke, will make more power and if you don't give them the right fuel, you won't realize that power. You'll lose it from either pre-ignition or our engine will retard the timing (which most if not all can do on the fly these days). If you give a standard compression engine higher octane, it will still work but you will not see any measurable benefit. If you do then the engine wasn't designed well in the first place or something else is going on.
Speaking of timing, THAT is what the different octane rated fuels offer. The higher the number, the more you can compress it without it igniting itself (which happens from the heat buildup) AND the longer it will burn in the cylinder. If the piston hasn't reached the bottom of the stroke when the fuel has finished burning, power and efficiency is lost even if the lower octane fuel made it until the spark plug fired. Worse though is when it ignites early AND runs out of "gas" before pushing the piston all the way down. That's why it is important to use premium when the engine calls for it.
On the flip side, using 91 when your engine says 87 is all that's needed could result in the fuel still burning as it's being shoved out of the exhaust port. We're talking microseconds of difference here so it's not likely to be a huge issue. HOWEVER, now let's imagine 100LL (pure octane, NO hexane) in that same engine. Now you WILL be sending unburnt (or even still burning!) fuel out into your exhaust stream. What could be fun show when that unburnt (or still burning) fuel shoots out of your muffler is lost on a boat because the exhaust comes out underwater so you won't even see the fireworks! Oh yeah and let's not forget that 100LL, only available at small airports, makes even a greedy marina's price seem low!!
I know we've been taught more is better, higher numbers are better, ad nauseum, but try and unlearn that when it comes to fuel.
