Hermann
Site Donor 2023
I'm not a numbers person, I prefer "seat of the pants" and verifiable real world results. Not some dot on a graph or measurement gobbledygook, that means nothing to my real world observations.
Octane vs mpg again...
- Thread starter AZjeff
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“Real world” observations are the problem. Observation of something is the easy part, ascribing that observation to one isolated variable is the much more difficult part. Individuals on here try it all the time but it’s not possible in the real world. There are many, many uncontrolled variables in everyday driving, many of which can drive that one variable into the noise.
People often elevate “seat of the pants” and other ad hoc experiments to the level of a standardized experimental test but it’s only because they don’t have a clue what such testing requires and what it takes to show that an observation is the result of a specific variable. It happens all the time on here.
The hard truth is that virtually no one in the real world that performs tests does them in the “real world”. Hard to understand sometimes but true.
Hermann
Site Donor 2023
^^^^^^ Gobbledygook
I don't know what is more real than the picture of my dash, that is showing a noticeable increase in fuel mileage of 5% or so over what I normally get. The conditions were slightly worse than normal. I'm not blowing smoke up your wazoo, I have nothing to gain except more MPG's and passing on the observations I have made.
numbers people 
I'm so glad I'll be cremated by the time there is nothing real left in this world.
@kschachn So do I understand correctly that you are the camp that a motor designed to run on 87 does no better on 93?
With over a million miles on those 4 cars, have you run long term tests on any of them?
I'm with you, seat of the pants feelings can be and often are deceiving. It is also difficult to drive the exact same way in the same conditions from one tank of gas to another in my house these days. I run spreadsheets and have gotten more accurate results lately when I created a city/hwy usage for each tank of gas and gallons burned per hour in relation to the city/hwy percentages.
With over a million miles on those 4 cars, have you run long term tests on any of them?
I'm with you, seat of the pants feelings can be and often are deceiving. It is also difficult to drive the exact same way in the same conditions from one tank of gas to another in my house these days. I run spreadsheets and have gotten more accurate results lately when I created a city/hwy usage for each tank of gas and gallons burned per hour in relation to the city/hwy percentages.
Sure.^^^^^^ Gobbledygook
I don't know what is more real than the picture of my dash, that is showing a noticeable increase in fuel mileage of 5% or so over what I normally get. The conditions were slightly worse than normal. I'm not blowing smoke up your wazoo, I have nothing to gain except more MPG's and passing on the observations I have made.
I'm so glad I'll be cremated by the time there is nothing real left in this world.
Here’s another “gobbledygook” post from someone who knows a lot more than me, it’s about brand but it covers the problem with those real world measurements you’re so enamored with (wazoo or no wazoo):
https://bobistheoilguy.com/forums/threads/best-brand-of-gasoline.305463/page-4#post-5914788
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Tests? I have no tests I’ve run, sorry.
If an engine is capable of advancing the timing then it can take advantage of a higher octane fuel to be more efficient (you’ll do better by raising the compression ratio however). But since there are multiple ways to affect the rating and those may increase or decrease the energy content, it’s never an absolute based solely on the rating.
Unless there is some long term verification, I don't buy that significant of a difference due to just higher octane fuel. If its based on this tank, I got this mileage, and that tank got that mileage - were the conditions identical? And I mean, identical. Towing routes and speeds the same, wind direction the exact same and strength? Same temps? Etc... When towing a trailer, the wind direction and strength can make all the difference.
I can tell you with 6+ years of fueling records from my 2.7 ecoboost F150, I do see an increase in mileage using premium. As others have noted, much of that can be traced to it being E0 in many cases, versus the E10 87 octane. Otherwise I don't notice a difference in mileage.
And theres a comment up there on the advanced timing making it so E85 delivers similar fuel mileage... I can tell you with hundreds of flex fuel trucks in our fleet, the E85 fillups reliably deliver lower fuel mileage - by 16-25% depending on the unit...
I can tell you with 6+ years of fueling records from my 2.7 ecoboost F150, I do see an increase in mileage using premium. As others have noted, much of that can be traced to it being E0 in many cases, versus the E10 87 octane. Otherwise I don't notice a difference in mileage.
And theres a comment up there on the advanced timing making it so E85 delivers similar fuel mileage... I can tell you with hundreds of flex fuel trucks in our fleet, the E85 fillups reliably deliver lower fuel mileage - by 16-25% depending on the unit...
That's not in dispute though. E85 at its maximum ethanol has about 73% of the energy content of typical E10. But the timing advance makes up for the lower energy content with better efficiency.
"verifiable real world results" here would be multiple tanks on either fuel (hand calculate tanks, not the dash readout) and including enough tanks to help smooth out all the variables that impact mpgs on a daily basis. Not gobbledygook, but actual results that can be used to say what you are saying.
It's just math with the E thing - you get worse mpgs but it costs less. How much worse mpgs vs. cost is what answers that question. The timing dvance gives you more power (IF you even are taking advantage of it), but you are using more fuel.
You stated:
Absolutely a higher octane rating allows timing advance and better fuel economy relative to the fuel content. That's why E85 is reasonably close to the fuel economy of gasoline.
It is not "close" to the fuel economy of regular E0 or E10. With a fleet of 200+ flex fuel vehicles running both E85 and E10, I can state that on average the E85 fillups net an average of 20% lower fuel mileage in our fleet. The individual unit and usage make it vary between 16 and 23% lower... While timing can advance to take advantage of octane, it cannot make up for the energy deficit.
Again, I don't consider 20% lower to be close to the same...
Hermann
Site Donor 2023
All of my tanks are hand calculated at Fuelly.com in my link. The MM in the truck is typically 2-2.5 mpg optimistic. That's what's in brackets in my notes. In a few more tanks which takes months IMW, operating conditions will change. After this fill there will probably be only one more tank with similar operating conditions using A/C all the time. I have more fuel savers for the next tank to run the 91 octane E0. I guess we will see if the uptrend in MPG's continues.
@kschachn my Sam's Club premium purchases are for the Motorcycle .
It does?
It's fun to cruise with guys on E85, they have to stop to fill up as often as I have to pee! E85 gets horrible mpgs but again, you also pay less...math is what it is on this.
That's quite revealing man. Thirty plus years ago I proved that and engine that does not advance timing or change fuel delivery also runs more efficiently on higher octane versus lower octane fuels. As Doctor Fauci says, "It's just common sense".
That’s cool.That's quite revealing man. Thirty plus years ago I proved that and engine that does not advance timing or change fuel delivery also runs more efficiently on higher octane versus lower octane fuels. As Doctor Fauci says, "It's just common sense".
Where is this body of work?That's quite revealing man. Thirty plus years ago I proved that and engine that does not advance timing or change fuel delivery also runs more efficiently on higher octane versus lower octane fuels. As Doctor Fauci says, "It's just common sense".
Well, today it resides in my head. I threw away all the little note pads from the cars a few years ago when cleaning out the garage. I do however have detailed logs in excel spreadsheets for my two trucks.
Right after purchasing the Yukon, I ran a couple of tanks of 87 and she ran like crap compared with 93 and so, like all of my older vehicles, we run 93 in the Yukon's 5.3 as well. It was tuned to to burn 91+ shortly after those tests 5 years ago. But the tests since compare 93 and varying levels of ethanol.
The Sierra has the 6.2 motor and has always been fueled with 93 or E85. It's engine will be tuned shortly.
Here to learn and even have my data peer reviewed as I'm interested in truth and not too proud to admit when I'm wrong.
We need more data.
If data logging shows no KR running 87 octane and both fuels are either E0 -OR- E10, there will be no difference in fuel mileage between the two different octane rated fuels.
If the 87 was E10 and the 93 was E0, then you will see better fuel economy with the E0, regardless of what the octane rating is.
Unless the higher octane fuel is slowing combustion down enough to eliminate any KR, there will be no difference in fuel economy.
Have you run and maybe documented such yourself? I've never seen this to be true excepting DI engines and even they see differences in efficiency between brands of fuel even.
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