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elcabron 12-10-2009 08:57 PM

Fuel economy vs gas octane
Hi everyone, since the gas prices are getting high I was wondering if there is any change in the performance of the truck and in the gas consumption if I use 87 octane gas or if I use 92 octane gas. I have the 5.7 Hemi, and as far as I know it shouldn't be any problem to the engine, but again, my concern is about the mileage


RamTech 12-10-2009 09:11 PM

Use the octane recommended. Lower octane can result in spark knock and there is no real benefit in running higher octane.

Dan 12-10-2009 10:44 PM

when I first got my truck (and before I got my predator) I tried 87, 89, and 93 octane gas and there wasn't a noticable difference in fuel economy or power

CdnoilRAM 12-10-2009 11:13 PM

Chrysler recommends 89 for the HEMI, and from general concensus from similar questions you can run 87 with little to no problems, only run 91+ if you're running a tuner.

GPSHSLAX 12-11-2009 12:46 AM

The octane number you see on the gas pump is an indicator is preignition resistant. That's it. Is has nothing to do with fuel economy. In fact higher octane fuel has more addatives to affect that property and theoretically results in lower enegry desity and fuel economy. In practice the difference is unnoticably small and there is no change in MPG based on gas octane.

kcslc 12-11-2009 04:27 PM

I'd agree with most everything said so far. Running a lower octane than recommended will increase your chances of pre-ignition (aka detonation, knocking, pinging). Your truck has a knock sensor and if knock occurs will recognize this as being damaging to its longevity and will retard the timing appropriately to compensate. Retarded timing will equate to lower power and I would assume less efficiency. What does this mean in plain english? Run a lower octane and watch your mileage. If it decreases a noticeable amount step back up to the recommended octane.

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