Re: some question for overland owners
Higher octane gasoline prevents pre-detonation (knocking) in higher performance engines. Most modern high performance engines, including the 5.7L Hemi, have knock detectors that tell the computer when it is starting to knock, and then the computer retards the timing so that the knocking is avoided before a human could even detect that there was any knocking to begin with. The timing retardation does affect performance and fuel economy, so to get the best performance and fuel economy you should use 89 octane gasoline.
How much does it affect it? I can't say that everyone will get the same results, but my average fuel economy on my daily commutes increased about 1 mpg (from 13.5 to 14.5) when I switched.
You pay 10 cents more per gallon for 89 octane over 87, that works out to around $2.40 per 24 gallon tankful (if you almost run it dry). At 13.5 mpg, you can go 324 miles on that 24 gallon tankful of 87 octane gas. If you were to use 89 octane gas instead and go the same 324 miles, you would only use 22.3 gallons of gas, and would have 1.7 gallons of 89 octane gasoline left. At today's average prices, 1.7 gallons of 89 octane is more than double the $2.00 you saved by filling the tank with 87 octane, so it's actually cheaper in the long run to use 89 octane, as you go further between fill ups, or at least don't have to put quite as much in when you do fill it up.
Sean in PA
2011 Jeep Grand Cherokee Overland
5.7 Liter Hemi V-8
Adaptive Cruise & Blind Spot Monitoring