lineman_16735

As was said, there is no gain to be had, mileage wise with increased octane. I personally stay away from Shell. In my experience the additives Shell uses will build up quickly on your plugs.

EBinMT

I noticed the biggest difference going from Exxon Midgrade w/out ethanol (same price as 87 here) to Cenex Midgrade. i observed nearly 20% loss of mileage!!! I don't know if that was bad gas, too much ethanol, both or what ever else. I do know that I am not the only one to notice. I am an avid biker and we were talking about mileage this fall and a fellow rider claimed he lost nearly 6-8mpg running cenex fuel vs the other brands available here; Exxon, Conocco, Sinclair, and Blue Planet(holiday).

So personally I believe it the composition of the fuel going in has a bigger effect than the actual octane as many areas cut lower octane fuels with ethanol to increase the octane rating. This works, but MPGs will suffer.

Joewee3.5

A 60 year old with an 80 IQ is double my age but doesn't make them smarter than me. I've only used 93 oct, both ethanol-free and 10% ethanol, and my mileage varies 1-2 mpg per tank. I drive nearly the same route, speed and under 2500rpm acceleration. You don't have to care about my opinion but I assure you everyone that documents there mileage and octane usage will agree that octane has no effect on mileage.

Theocoog

I have to ask because I am curious: if octane has no effect on mileage, as you state here, why do you bother paying extra for 93 octane all the time?

Edit: I'm not saying I don't agree with you, it just doesn't make sense to me. Maybe you have other reasons for spending more for higher octane gas.

DieselDawg

Octane dictates how much compression the fuel can withstand before detonation...it does not increase the BTUs of the fuel. The power that results from using a higher octane is a result of a higher compression engine and/or advanced timing. Octane by itself does nothing to increase power or energy value of a gallon of fuel.

Octane is used to avoid pre-detonation or self-ignition without a spark. It is the opposite of Cetane which is the value looked at when using Diesel...you want a High Cetane Number (the higher the Cetane the lower the Octane) to give Diesel a quicker "fire" under compression without a spark.

For Gas, at most retail outlets, they blend in Ethanol which delivers a higher Octane Number...BUT...it yields a Lower BTU Value per gallon (hence lower mpg with this blend). You just can not ignore the specific values of fuels.

Gas ................. 114,000 BTUs/Gallon
Summer Gas ......114,500 BTUs/Gallon
Winter Gas ....... 112,500 BTUs/Gallon
Ethanol Blend ... 111,836 BTUs/Gallon
Diesel .............. 129,500 BTUs/Gallon

Bottom Line: You can not get more energy out of a gallon of anything than the BTUs contained in that said gallon.

JJKJ

iTrader: (2)

Great post DD. Your first paragraph explains why SOME vehicles can experience better economy from higher octane fuel. What no one is discussing here is that internal combustion engines are not anywhere near 100% efficient. There is always some amount of unburnt mixture with each combustion event. IF higher octane fuel allows the engine to take advantage of a more efficient timing curve, then it will increase power and efficiency (economy). Many non-performance-oriented vehicles do not have aggressive timing curves that can take advantage of higher octane fuels. In those type of vehicles, high-octane fuel can actually decrease fuel economy because the higher octane fuel's resistance to burn will result in more unburnt mixture being exhausted instead of burnt. I believe the Eco ECU probably (don't know for sure) has a timing curve available that takes advantage of higher octane fuel because Ford states in all of it's literature that hp/torque ratings are obtained using high-octane fuel.

champ198

I haven't noticed any better mileage or performance on 93 vs 87; however, I have found significant improvements with the use of non-ethanol fuel. I get up to 2 mpg better on the interstate (70mph) with non-ethanol fuel. The engine seems to idle smoother on non-ethanol fuel.

hillwood24

Where can you find non ethanol fuel? All the ones around here say up to 10% ethanol. And ethanol is such a joke too. Costs more to make than its worth, and we get terrible mileage as a result. Reminds me why I vote Republican.

3point5

I agree with Joe…

Higher octane fuel is simply more stable at higher compressions…that's it!!

any increases in mpg's / performance and simply a combination of inconsistencies in your 'analysis'...

such as:
driving conditions
driving styles
vehicle dynamics
road/environmental conditions (temp, winds, incline/decline, moisture)
different sources of fuel (from the refinery to the gas station)
mixing fuels in storage tanks prior to the gas station

etc.

There are WAY too many inconsistency to even think that someone, in their daily drive, can formulate a scientific difference.

Theocoog

So if Joewee3.5 is calling BS on higher octane getting better gas mileage and you are agreeing, can one of you please explain why Joewee3.5 only uses 93 octane?

Like I said earlier, I'm not disagreeing with you. I just want to understand why someone would pay extra for premium when they don't get any benefit from it. What else is there that I'm missing?