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Old 12-31-2020, 08:15 AM   #1
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My “Real Gas” Experiment

Ever since purchasing my truck in 2015, I have always wondered what kind of a MPG difference using non-ethanol fuel would make. I have never been in a position to be able to do this until last weekend.

My tank was as close to empty as it could get and I was sweating it getting to a nearby gas station that I have never used before, and it just happened that they had some pumps with non-ethanol, 89% octane gasoline. It cost 30 cents per gallon more than the 10% ethanol, 87% octane regular gasoline that I normally use, but that didn’t matter to me this time. I filled-up with over 34 gallons.

I had a 150-mile drive (not towing) ahead of me on a route I take regularly, mostly on I-95 through Maryland and Virginia. I always, always make this trip at 14.6 to 15.4MPG. My average speed for this trip almost always clocks-in at 60MPH from door to door.

I can’t say that I noticed any difference in performance using the non-ethanol gas, but there may have been some — I just don’t know — but the big difference I did notice was, I got 19.4MPG on this trip. I made the entire trip in exactly 2-1/2 hours, which was right on par with my average speed for this trip — there is very little secondary road travel (about 30 miles) and almost all interstate travel.

I haven’t yet done the math to see if the difference in price was worth it, but I thought I would share this much for people who wonder what the difference of using the non-ethanol gas does for MPG. I was impressed.

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Old 12-31-2020, 08:35 AM   #2
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I’m not a chemist or an automobile engineer, but here is how I looked at this from a layman’s point of view. Charts are available showing the BTU content of various fuels. If I remember correctly from doing the math on ethanol vs gasoline, I calculated an approximate 3% difference in BTU content between 100% gasoline and 10% ethanol/gasoline blend. When I did many tanks of mileage tests on a carbureted motorcycle using 100% gasoline vs 10% ethanol blend, I did indeed measure around 3% difference in fuel economy, as expected. For me, price differences between pure gasoline and ethanol blend are too high to justify buying pure gasoline just for the small fuel economy gain. I buy 10% ethanol blend because it takes me the most distance for the money. Assuming the engine is able to properly use the various fuels, it pretty much boils down to math.

As always, “your mileage may vary.”

https://en.wikipedia.org/wiki/Gasoli...lon_equivalent

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Old 12-31-2020, 10:23 AM   #3
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I took a less scientific approach once comparing regular 87 octane and premium 93 octane. I compared cost per mile instead of miles per gallon. The cost was very close but performance was better.
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Old 12-31-2020, 10:57 AM   #4
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Originally Posted by Sunseeker16 View Post
I took a less scientific approach once comparing regular 87 octane and premium 93 octane. I compared cost per mile instead of miles per gallon. The cost was very close but performance was better.
Did you do this comparison using the engine of your Sunseeker?
Am I correct in saying you have the Ford V10 engine?
What performance was better? I have no complaints from my V10 using regular unleaded with 10% ethanol, which is the normal fuel at pumps along the way.
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Old 12-31-2020, 11:42 AM   #5
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I took a less scientific approach once comparing regular 87 octane and premium 93 octane. I compared cost per mile instead of miles per gallon. The cost was very close but performance was better.
I gathered that the original post in this thread was about ethanol blend vs pure gas. So are you now comparing strictly octane varieties, without regards to ethanol content?

That the "performance is better" is difficult to measure or convey to others. What does the mean in your case? The performance of our Sunseeker has been just fine.
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Old 12-31-2020, 12:34 PM   #6
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You got 15.4mpg on 90% pure gas and 10% ethanol. Ethanol has energy so it was contributing to your mileage...but lets eliminate it altogether. So we will say you got 15.4 mpg on just 90% gas.

If you add the ten percent back by filling up with pure gas you should only be able to see an increase of 10% mpg. Which would give you a 1.54 mpg improvement or 16.94 mpg. Your improvement to 19.4 is a 26% increase while totally discounting that ethanol was providing any energy.

I'm guessing you had a considerable tail wind.
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Old 12-31-2020, 12:47 PM   #7
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Yes I did the comparison using fuel with 10% ethanol. As for performance you are correct the V 10 does a pretty darn good job on 87 octane. I normally run 87 but do use 93 at times. Like most folks here, I am mechanically inclined and very in-tune with my vehicles so I probably notice things good and bad that a lot of people wouldn't. As an example, my performance comparison is based on towing my 2012 Ford Escape over a frequently traveled hilly route. If I happen to have a tank of 87 it shifts down to the point where the V 10 screams. When I have a tank of 93, not so much. It just seems to pull better and shift less. I get it, when the V 10 screams it's working and making power.
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Old 12-31-2020, 01:41 PM   #8
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You got 15.4mpg on 90% pure gas and 10% ethanol. Ethanol has energy so it was contributing to your mileage...but lets eliminate it altogether. So we will say you got 15.4 mpg on just 90% gas.

If you add the ten percent back by filling up with pure gas you should only be able to see an increase of 10% mpg. Which would give you a 1.54 mpg improvement or 16.94 mpg. Your improvement to 19.4 is a 26% increase while totally discounting that ethanol was providing any energy.

I'm guessing you had a considerable tail wind.
Could there be any other factors involved, because I really don’t think I had a strong north wind pushing me down I-95 south, and I definitely wasn’t driving any more conservatively than usual.

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Old 12-31-2020, 01:57 PM   #9
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You got 15.4mpg on 90% pure gas and 10% ethanol. Ethanol has energy so it was contributing to your mileage...but lets eliminate it altogether. So we will say you got 15.4 mpg on just 90% gas.

If you add the ten percent back by filling up with pure gas you should only be able to see an increase of 10% mpg. Which would give you a 1.54 mpg improvement or 16.94 mpg. Your improvement to 19.4 is a 26% increase while totally discounting that ethanol was providing any energy.

I'm guessing you had a considerable tail wind.

Don't think it is that simple . octane with the 10%E was 87 pure was 89 so the engine control may have made and probably did change the spark advance /retard which could cause an even greater mpg .
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Old 12-31-2020, 03:32 PM   #10
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Taking your normal mileage using 87 leaded which I'll call 15.0 mpg (the midpoint of your 14.6 - 15.4 range) and the 19.4 mpg you got on this trip using 89 unleaded, your increase in mileage is 4.4 mpg, or 29.3%

I have tried this identical experiment a number of times over the years in various vehicles including:

1987 Nissan Pathfinder w/ 3.0-liter V6
1995 Jeep Wrangler Sahara w/ 4.0 l 6 cyl
2013 Honda CRV w/ 2.4 l 4 cyl
2014 Toyota Tundra w/ 4.6 l V*

I am presently running a similar test on a 2021 Jeep Wrangler Sport with a 2.0 l 4 cylinder turbocharged engine where I am comparing the recommended 87 octane unleaded with the also recommended 93 octane.

Not a single one of these tests gave me a mileage increase using ethanol free 89 octane gas that was beyond barely perceptible (if that) let alone anywhere near your 29+%. I wasn't in the truck with you, so I clearly can't challenge your reported mileage, but I'll bet my rear end it was not the result of using 89 octane ethanol free gas.
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Old 12-31-2020, 04:36 PM   #11
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Might a slight loss in power with 10% at 87 compared to straight gas at 89 while towing cause enough of a downshift pattern to effect mileage?
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Old 12-31-2020, 04:43 PM   #12
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Taking your normal mileage using 87 leaded which I'll call 15.0 mpg (the midpoint of your 14.6 - 15.4 range) and the 19.4 mpg you got on this trip using 89 unleaded, your increase in mileage is 4.4 mpg, or 29.3%

I have tried this identical experiment a number of times over the years in various vehicles including:

1987 Nissan Pathfinder w/ 3.0-liter V6
1995 Jeep Wrangler Sahara w/ 4.0 l 6 cyl
2013 Honda CRV w/ 2.4 l 4 cyl
2014 Toyota Tundra w/ 4.6 l V*

I am presently running a similar test on a 2021 Jeep Wrangler Sport with a 2.0 l 4 cylinder turbocharged engine where I am comparing the recommended 87 octane unleaded with the also recommended 93 octane.

Not a single one of these tests gave me a mileage increase using ethanol free 89 octane gas that was beyond barely perceptible (if that) let alone anywhere near your 29+%. I wasn't in the truck with you, so I clearly can't challenge your reported mileage, but I'll bet my rear end it was not the result of using 89 octane ethanol free gas.
About 15 years ago or so, I had read an article that suggested that not all fuel brands contained the same amount of energy per unit. The author claimed that some of the "off brands" caused lower gas mileage because the gas just had less "oomph".

At the time, I was driving the F150 in my signature around 3,500 miles per month (42k-44k/year) for work, and the cost of gas was milking me dry. So I did a 4-month test. The first month, I used the same Arco gas that I had always used, but I kept track of my miles, fuel usage, and cost in a notebook. The second month, I ran only Chevron and kept the same records. The third month I went back to Arco, and for the fourth I did Chevron again. Over 10,000 miles of records to compare.

I found that my MPG was *slightly* better on Chevron. More than 1%, but less than 2% if I remember correctly - but when I calculated it as "cost of fuel per mile" it was almost identical, despite the Chevron gas being 20 cents+ more expensive per gallon.

So I was paying maybe $4 more for each tank of Chevron gas, but I was buying gas less often.

Since it was a wash, cost-wise, I decided to stick with the name-brand gas. (I also bought a 2nd car that got 30 mpg to use for work!)
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Old 01-01-2021, 07:38 AM   #13
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Don't think it is that simple . octane with the 10%E was 87 pure was 89 so the engine control may have made and probably did change the spark advance /retard which could cause an even greater mpg .
Nomad reported an average of 15mpg for his trips on 87 pump gas with 10%E.
He reported 19.4 on 89 pure gas. That is a 29.3% increase.

The energy in ethanol is measurable and known. Ethanol has 33% less energy than gasoline. Only 10% of the 87 octane pump gas is ethanol which equates to a difference of 3.3% in energy content between pure gas and gas with 10% E.

So we subtract the 3.3 from the claimed 29.3% increase in mpg and we are left with a 26% increase that can't be accounted for by difference in energy content between the two.

I went over that so we are all on the same page...so are you suggesting his truck, which was designed to run on 87, had a 26% increase in mpg due to the +2 octane increase?
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Old 01-01-2021, 09:00 AM   #14
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Does the v-10 PCM keep track of octane adjust ratio? My 7.3 does. You definitely get better OAR on higher octane top tier fuel than with 87. But it can take over one tank full to fully adjust in my experience. With better OAR, you do see extra timing added in the form of negative knock reduction. On some trucks I see the torque converter lock up more with higher octane, especially in cruise control, which helps efficiency significantly.
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Old 01-02-2021, 07:11 PM   #15
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When I use e85 in my suburban vs regular 87 my milage drops roughly 25%. There is a negligible difference with pure gasoline.
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Old 01-03-2021, 09:05 AM   #16
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Nomad reported an average of 15mpg for his trips on 87 pump gas with 10%E.
He reported 19.4 on 89 pure gas. That is a 29.3% increase.

The energy in ethanol is measurable and known. Ethanol has 33% less energy than gasoline. Only 10% of the 87 octane pump gas is ethanol which equates to a difference of 3.3% in energy content between pure gas and gas with 10% E.

So we subtract the 3.3 from the claimed 29.3% increase in mpg and we are left with a 26% increase that can't be accounted for by difference in energy content between the two.

I went over that so we are all on the same page...so are you suggesting his truck, which was designed to run on 87, had a 26% increase in mpg due to the +2 octane increase?

I have no idea what nomads actual mpg was . i did state that with a higher octane the computer will change the spark timing to adjust for anti knock and can give higher mpg then expected . it's not all math on paper . you did not take into account the advance spark differences associated with higher octane and the lack of ethanol. I know i see close to 10% mpg gain with non ethanol 92 oct compared to 87 10% ethanol .
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Old 01-03-2021, 09:19 AM   #17
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I don’t know why some of you haven’t just come right out and called me a liar.

I shared what I experienced, only to be told I am wrong by a few people. I’m not wrong. I am perfectly capable of properly using basic math.

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Old 01-03-2021, 10:16 AM   #18
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I have no idea what nomads actual mpg was . i did state that with a higher octane the computer will change the spark timing to adjust for anti knock and can give higher mpg then expected . it's not all math on paper . you did not take into account the advance spark differences associated with higher octane and the lack of ethanol. I know i see close to 10% mpg gain with non ethanol 92 oct compared to 87 10% ethanol .
Exactly. Some NA engines will advance spark 6 degrees over base timing with sustained low knock (a good OAR reading), and 10 or 12 degrees over knock reduction timing which you can get in some 87 octane fuel and engine combinations. In addition I have observed that when OAR is good, at least with cruise control, the transmission torque converter locks up more, and more often, even as a higher gear is held. In the right rolling hill conditions, this can lead to significant efficiency improvements. Much larger than the simple btu difference in the fuel. An engine designed to run a recommended 87 octane fuel does not mean it was designed specifically *for* 87. Often engines that can run on 87 will take full advantage of 93 or even 94 octane. Not sure about the v10 as I don’t think it ever got VVT, but I bet it can with timing advance.
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Old 01-03-2021, 10:30 AM   #19
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Originally Posted by MR.M View Post
I have no idea what nomads actual mpg was . i did state that with a higher octane the computer will change the spark timing to adjust for anti knock and can give higher mpg then expected . it's not all math on paper . you did not take into account the advance spark differences associated with higher octane and the lack of ethanol. I know i see close to 10% mpg gain with non ethanol 92 oct compared to 87 10% ethanol .
I absolutely did take the octane difference into account and left it out on purpose. This octane difference is a variable and impossible to measure except with the motor doing the test. I simply did some math to show an extreme % of difference has to be accounted for.

And, what you said was this:
Quote:
Originally Posted by MR.M View Post
Don't think it is that simple . octane with the 10%E was 87 pure was 89 so the engine control may have made and probably did change the spark advance /retard which could cause an even greater mpg.
Considering you quoted me and given your vague text one could easily interpret you meant an even greater % than what I was talking about. Because of that (for clarification on your belief) I asked if you are suggesting his truck, which was designed to run on 87, had a 26% increase in mpg due to the +2 octane increase?

Seemed reasonable to me.
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Old 01-03-2021, 10:35 AM   #20
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Exactly. Some NA engines will advance spark 6 degrees over base timing with sustained low knock (a good OAR reading), and 10 or 12 degrees over knock reduction timing which you can get in some 87 octane fuel and engine combinations. In addition I have observed that when OAR is good, at least with cruise control, the transmission torque converter locks up more, and more often, even as a higher gear is held. In the right rolling hill conditions, this can lead to significant efficiency improvements. Much larger than the simple btu difference in the fuel. An engine designed to run a recommended 87 octane fuel does not mean it was designed specifically *for* 87. Often engines that can run on 87 will take full advantage of 93 or even 94 octane. Not sure about the v10 as I don’t think it ever got VVT, but I bet it can with timing advance.
Are you suggesting timing and torque converter lock-up can account for the 26% increase in mpg?
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