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That makes sense. But how does that relate to the 17 mpg city estimate I have on my window sticker(4x4, crewcab, Laramie, short bed, 3.92) ? Shouldn't city mpg not be as affected by the 392 rear and the ram be able to hit this EPA estimate?
I've been experimenting with driving styles and my 4x4 Limited Etorque with ORP gets 14-15 City when I go with the flow and pay no attention to speed, braking, etc. When I've intentionally attempted to keep the instantanious mpg readout as high as possible, I got 20 mpg in the city. Not my style but proves it is possible. Driving aggressively, I got 12 mpg.
Good information. Thank you. I'll have to try being super conservative with it for a tank or two and see what I get. I'm normally slow and smooth driving in the city but not looking at the mpg gauge. I'm getting around 14-15 mpg city with 89 octane.
The Hemi's compression and timing are designed for 89 octane. 87 works fine but timing will be retarded if pinging is detected. Altitude, ambiant and engine temperature, and engine load are factors that may cause pinging. A slight reduction in power and economy may be noticed. It's minimal since most don't drive under heavy loads where economy would be poor anyways.
Exactly. Higher altitude reduces compression as well. I'm sure 87 is fine there. My built Harley is prone to pinging at low altitude on 93 octane but runs great at 8000 ft. on 89 octane.
There is a general belief by some that octane affects economy. As long as the motor isn't pinging, that's not true.
There exists the possibility of manufacturing tolerance leading to one engine that requires 87 to achieve optimal performance, while a "hot" build (an engine that happens to end up with slightly higher compression from the factory) ends up performing better on a higher grade. It's also possible that the computer senses the higher grades and advances timing accordingly. I started with premium (93) in my truck out of habit, and then I switched to 89. I'm a couple of tankfuls into 89 and have been consistently seeing a reduction of 1+ mpg thus far compared to 93, despite efforts to maximize economy. I did not expect to see a difference. All tanks have had approximately 10% ethanol, so I don't believe it's the determining factor.
Throw an emulsifier in it.
Manufacturer RECOMMENDS 89. ACCEPTABLE is 87. Denser air does not help when fuel quality takes a nosedive during the winter.
