[swiego29382]

My LCI X5M is approaching 2,000 miles.

Bring a California vehicle, 91 octane is the only fuel I was aware about so that is what I have been using. First ~1,300 miles that was the fuel. No issues obviously. First few refills the range reports 394 miles immediately after refueling.

Then I discovered a station not too far from me that sells 94, 96, 98 and 101 and thought, hey why not try 94 and see what happens?

Observations:
- the first time I filled from near empty, range was 394 as before. However then I had to drive places and for the next 40 or so miles the range continued to report 394 or even increase a few miles.
- second refill (again 94 from empty tank) range after refuel went up to 445.
- I have not been tracking whether actual range is any different or if this is just estimation error in software
- I sense mpg is some 2mpg higher at highway speeds but this is anecdotal and even if real it may be due to engine breaking in etc.
- absolutely no discernible difference in performance
- that said, I feel that after it’s warm engine idle is a bit quieter

Anyhow, wanted to share the results of the experiment. Not sure if I’ll continue it. 94 is definitely more expensive—not enough to discourage some experiments but I am not sure I would keep it up.

I’m also assuming filling with something like the station’s 96 (or blending 94+96) is a waste of $ but happy to do more experiments if there is reason to believe a S68 engine would react to it positively.

[crazyinp]

Which station are you referring to? The only one that I am aware left with those options is the Sunol.

[Jeff J]

What's the ethanol content of the fuel in question? Finding straight gas (10% or less ethanol) at octanes of 93 or above is very rare. Around here any kind of 93 is rare, and most of those are 30% ethanol. Some will say that's not great for the fuel system as a daily driver.

[swiego29382]

Originally Posted by crazyinp

Which station are you referring to? The only one that I am aware left with those options is the Sunol.

It’s indeed the one in Sunol.

[BobsM3Coupe]

I would bet that our X5M's are losing 10 hp or so between the 91 and 93 octane fuel.
Car & Driver (link below) dyno tested the F90 (M5) with 91 vs 93 octane fuel, and it showed a 13 hp loss naturally due to the different octane levels. And it did show a tenth slower in the 0-60, 0-100 and 1/4 mile times. Yet torque and mpg were improved with the 91 octane.

https://www.caranddriver.com/feature...dodge-charger/

[crazyinp]

Originally Posted by BobsM3Coupe

I would bet that our X5M's are losing 10 hp or so between the 91 and 93 octane fuel.
Car & Driver (link below) dyno tested the F90 (M5) with 91 vs 93 octane fuel, and it showed a 13 hp loss naturally due to the different octane levels. And it did show a tenth slower in the 0-60, 0-100 and 1/4 mile times. Yet torque and mpg were improved with the 91 octane.

https://www.caranddriver.com/feature...dodge-charger/

Besides the gas station above that I would stop by if I am in pass by, I use the one in Saratoga right before you get on rt9 it still has 100octane, so I would usually mix with 91 to make it 95

[eelnoraa]

Originally Posted by Jeff J

What's the ethanol content of the fuel in question? Finding straight gas (10% or less ethanol) at octanes of 93 or above is very rare. Around here any kind of 93 is rare, and most of those are 30% ethanol. Some will say that's not great for the fuel system as a daily driver.

This is very good point. It is easy to increase AKI by adding ethanol. Usually this happen in gas stations that is away from tracks. But I still don’t understand how this can increase mpg. Not doubting OP’s observation, but is it possible that the fact you get out of your way to get high octane gas change the driving pattern enough to increase average mpg, such as more highway driving per tank?

[CT335xi]

Originally Posted by eelnoraa

This is very good point. It is easy to increase AKI by adding ethanol. Usually this happen in gas stations that is away from tracks. But I still don’t understand how this can increase mpg. Not doubting OP’s observation, but is it possible that the fact you get out of your way to get high octane gas change the driving pattern enough to increase average mpg, such as more highway driving per tank?

I agree because as far as I know fuel with more ethanol gets worse mpg , like e85 probably 25-30% less.