Originally Posted by silverbullet
running higher octane in a vehicle designed for 87 can do some serious internal engine damage if run for a longer period of time. From a longevity stand point I wouldn't recommend it.
Octane is a rating system for the ease of ignition of gasoline. It is still just gasoline. Higher octane fuel is harder to ignite, but still burns just fine. It will not cause any damage to engine internals. It will reduce power output. An engine will always produce the most power it can(with its settings and tune) on the lowest Octane it can safely run.
That said, if you run too LOW of an Octane fuel in an engine designed for higher it could cause serious engine damage. An engine designed to run on 91+ fuel has some characteristics requiring higher Octane. Say higher engine compression ratio, boosted applications raising the effective compression(turbo/supercharged) or the timing characterstics. Basically the only thing in chips and programmers that requires a higher fuel octane level is usually total timing and the timing curve.
If your car or tune are supposed to run on 87, running 89, 91, 93, or 94 isn't gaining you any power, but it isn't hurting the engine any.
Sorry to go off on that. Now Water/Meth does NOT raise Octane rating. What it does is cool the intake air charge and reduce cylinder temperature. That lowers the octane requirement. Like the old story of a top fuel dragster burning out their spark plugs by the 1/8" mile and just running on the hot metal the rest of the way. A hot spot in a cylinder head can cause pre-mature ignition(commonly referred to as detonation). Which causes serious engine issues. Water/Meth helps reduce temperatures preventing that occurance. Diesels don't have Octane ratings, they go off Cetane, and for them Water/Meth is just reducing intake air charge temperature. Cooler air is denser air. Denser air means more air, so you can get more fuel.
Here is a video I just found that is actually pretty good:
Now with all that said. Water/Meth will serve no purpose for you. It isn't meant to be injecting ALL the time, so it wouldn't function for your raised octane requirement. Also it isn't intended for Naturally Aspirated engines at all. They just don't have the same situations that forced induction does. May it make a difference? A bit. Any noticeable difference? No.
If you live somewhere you cannot get access to the octane requirement for the tune or modification you want, look harder, or don't do it. Running on too low of an octane could cause SERIOUS engine damage. And all it takes it that one time you are away from the one station around that sells 91 octane.
Oh and Octane booster additives are not a safe alternative either. Don't go thinking you can run a hotter tune if you just dump an $8 bottle in at every gas fill up.