Z4M = 32MPG

[DarkstarZero]

Usually I can nurse 24MPG out of my Z4M on the highway, can't really average much better than that over a long stretch.

So the other day, just for fun, I put 110 octane fuel in my ESS tuned Z4M. I've put 110 octane in before when it was stock and it made no difference at all but this time I averaged 32MPG at 70MPH over 10 miles with cruise control on. Now obviously I don't care about average MPG on the Z4M but without a dyno, these numbers really show just how much more efficient the engine can be with higher octane and a proper tune.

Great work ESS

[Swashplate]

Was that downhill with a tailwind?

[Crimson92]

lies, all lies!!!!

[O-cha]

That's weird, 110 octane actually has less energy then 93, it's good for making power but it shouldn't have really boosted efficiency. Octanes not necessary at low load cruising conditions.

[ZStig]

I get 40mpg!























(walking)

[RBull]

Originally Posted by O-cha

That's weird, 110 octane actually has less energy then 93, it's good for making power but it shouldn't have really boosted efficiency. Octanes not necessary at low load cruising conditions.

that's my understanding too.

[inTgr8r]

A 10 mile run is not a big enough sample to determine accurate mileage.

[RichardTS]

Originally Posted by O-cha

That's weird, 110 octane actually has less energy then 93, it's good for making power but it shouldn't have really boosted efficiency. Octanes not necessary at low load cruising conditions.

Actually octane is more important at low load cruising conditions because at small throttle openings the spark is advanced as much as the knock sensors will allow. Increasing octane reduces knock and allows the spark to advance further at small throttle openings. The only reason octane is a consideration at all is knock.

And, by the way, octane works by making gasoline burn slower and at a higher temperature. Not necessarily with less energy.

I can easily see the efficiency increase because gas mileage is related to spark advance. The more spark advance you can run at any given throttle opening the better the gas mileage will be. So, with 110 octane, knock is mitigated and the knock sensors will allow more spark advance than would ever be possible with 93 octane. The end result should be increase gas mileage.

Whether 32 mpg is achievable in an S54 I can't say. With 110 octane, the gas is most probably 100% gasoline with no ethanol. Just that difference alone would increase gas mileage. Theoretically and based on only available energy a vehicle that gets 24 mpg on pure gas will only get around 23 on gas with 10% ethanol.

[O-cha]

Originally Posted by RichardTS

Actually octane is more important at low load cruising conditions because at small throttle openings the spark is advanced as much as the knock sensors will allow. Increasing octane reduces knock and allows the spark to advance further at small throttle openings. The only reason octane is a consideration at all is knock.

And, by the way, octane works by making gasoline burn slower and at a higher temperature. Not necessarily with less energy.

I can easily see the efficiency increase because gas mileage is related to spark advance. The more spark advance you can run at any given throttle opening the better the gas mileage will be. So, with 110 octane, knock is mitigated and the knock sensors will allow more spark advance than would ever be possible with 93 octane. The end result should be increase gas mileage.

Whether 32 mpg is achievable in an S54 I can't say. With 110 octane, the gas is most probably 100% gasoline with no ethanol. Just that difference alone would increase gas mileage. Theoretically and based on only available energy a vehicle that gets 24 mpg on pure gas will only get around 23 on gas with 10% ethanol.

I think you largely misunderstood. Also the ECU is always trying to use a maximum advance, but it is more of a factor at full throttle where octane is the limiting factor, at cruise the timing is already extremely advanced because the effective octane is already very high, its more about keeping the spark at the right point to provide the highest piston acceleration from the least amount of fuel then it is to prevent the engine from knocking. Both instances share similarities but are different.


Also 110 octane absolutely contains less energy then 93.

[aerobod]

+1 ^

The other factor is that the most efficient engine map is usually aimed at the "recommended" octane for the vehicle. Fall back to a map with less advance across the range is used when knock is detected while using lower octane fuel, besides a bit of variance with different fuels and from vehicle to vehicle, using a higher octane fuel than recommended isn't going to do a lot, unless a remap of the ECU to user higher octane fuel has been done.

[Garyl53]

Is the high octane ethanol free? I would think even E10 would decrease mileage a bit over non ethanol gasoline?

[DarkstarZero]

The racing fuel that I used was ethanol free and ECU was tuned by ESS for 93 octane. I don't know much about how all this works, maybe the headers and intake helped as well. In any case, I encourage others with an ESS tune to try it out and post if you're getting around the same MPG at 70MPH with cruise control over some flat distance.

[Dammmittt]

How about I post my non-tune efficiency with 98 octane (euro) at 160 on the speedo?

[SteveInfante]

That would be awesome. I'm hoping to be able to test that myself in a couple of years.