Originally Posted by Smitty
The Octaine rating of a fuel has nothing to do with cleaning an engine, nor is it going to make your engine last longer. There is absolutely no benefit of running a higher octaine than an engine is designed for unless it has been modified in some way. Just because it costs more doesn't mean it is better.
Smitty is on the right track...
93/91 octane fuel doesn't do anything to "clean" your engine. Detergents are added to fuels to clean them. A fuel with a higher octane rating is actually "harder to burn or ignite" under compression. You may get a little more performance from a higher octane fuel if the timing is retarded allowing for more compression before the fuel is ignited by the spark plug. Using a low octane fuel in a high compression/high horsepower engine will lead to pre-detonation or "spark knock" because lower octane fuel ignites much easier.
I'm not sure if the computer in the Ram will retard the timing for higher/lower octane fuels automatically. If it does, the difference will probably be negligable unless your running at the track and using timing devices. Probably why we see the programmers like the Predator used with success.
The compression ratio of your Hemi engine determines the octane rating of the gas you should use your truck. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. My old Durango R/T required 93 octane fuel (printed on the gas cap). The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight. The disadvantage is that the higher octane gasoline for your engine usually costs more.
Octane is a product of the refining process. When you take crude oil and refine it, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels.
Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87% octane and 13% heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and should only be used in engines that do not exceed that compression ratio. Ninety-three-octane is 93% octane and 7% heptane (or other hydrocarbon) making it suitable for high horsepower engines because it won't ignite as easily under compression.
Dodge has the recommended fuel rating for a reason. Running 87 octane fuel probably won't cause detonation or spark knock (I've done it a few times with no problems). Just remember the computer is optimized for 89 octane fuel because of the compression ratio in the Hemi engine.
Just my 2 cents...