With the 5.7 I have been running 87 and once in a while I'll do a fill up with 89 or 93. Haven't seen alot of difference in the 87 vs. 89 myself, just wondering again what you guys might have experienced???

 

you shouldn't, they all should release the same amount of energy. there isn't an advantage to running a higher octane gas on an unmodified motor that can run lower octane gas. the two main componets of gas is octane (C8H18) and heptane (C7H16) the heptane in gas is what subseptable to detonation due to the fact that it cannot take compression, burns quickly, or take very high temps (diesel is mainly heptane, usually has an octane rating of about ~40) Octane helps negate the heptane shortcomings since it can be compressed, burns slower, and can stand higher temps without detonation. when you start screwing around with the way things burn, cylinder compression, cylinder temps, and a few more factors, you'll need to start running the higher octane gas. that's about what I can pull from my *** for now, I sure others will chime in.

 

I completely agree with ya. I have noticed at 4000ft, I get 2-3mpg better with 91 compared to 87. This was figured with a years driving my RCSB 04' 2WD and 7 Tanks my 05' ECSB 4wd. I ran 91 for 4 Tanks first then 3 on 87 and saw a noticable decrease in MPG. Same type of driving. I am using 91 again and MPG is back up to 21.5mpg.

 

I've read and been told that unless your engine is pinging, use the lowest grade you can or what it was designed for. A higher octane will not help performance and can actually hurt it by not burning up completely. With the knock sensors in modern day engines, they will hear pinging long before you should hear it and adjust the timing to get rid of it. If you can hear it, it's bad! The Hemi is designed for 89 for optimum performance and mpg according to the owners manual but you can run 87 if you want or can't get 89. It also says that there is no need to run 91 and it can actually hurt performance and mpg. I run 89 as the manual states, never tried 87, at .10 cents a gallon and $2 more a fill up, I don't worry about it.
Jim

 

Heh, even with the Superchips programmer on the performance setting I still only run 89. Haven't noticed any pinging or any other problems by doing so and the truck actually seems to run a little better then on 92. A lot cheaper too.