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MOAK

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Wernersville, PA, USA
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Donald
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Diehl
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My best friend is a petroleum engineer (I was the physics guy). We went through the math calculating energy density of pure gasoline vs ethanol. It turns out the amount you lose in fuel efficiency from using ethanol blends--because it has less energy per gallon, so you have to use more of it for the engine to do the same work--is almost directly proportional to the price difference. Funny how capitalism works :P .
The cost difference per mile may be true when comparing high MPG vehicles but when comparing 12-13 mpg versus 16-17mpg. The last time I calculated, it was hovering right around 2 cents a mile. 8,000 mile round trip tour = steak and salmon instead of chicken & burgers
 
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Lindenwood

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The cost difference per mile may be true when comparing high MPG vehicles but when comparing 12-13 mpg versus 16-17mpg. The last time I calculated, it was hovering right around 2 cents a mile. 8,000 mile round trip tour = steak and salmon instead of chicken & burgers
Fair enough! But, there must have been some other factor, because there certainly isn't anywhere near 30% more energy in pure gasoline than blended fuels, and knock resistance is the same regardless if blended status. Are you sure you arent comparing 91+ pure gasoline to 87 octane ethanol? The additional knock resistance of using 91, with an ECU designed to adjust timing advance in real time, certainly could make the differences you have seen.
 
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Prerunner1982

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Navina, Oklahoma
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B
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Just curious Jon, is your jeep a 6 cyl or V8 ? I have never heard of a 6 cyl ever needing anything other than regular unleaded gas unless the compression was raised to 10 to 1 or higher and have a hi performance cam.
Lanlubber
6 cylinder, runs fine off 87 octane and cheap copper plugs. 18 mpg average.
 
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Lanlubber

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Influencer I

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Mimbres, NM, USA
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6 cylinder, runs fine off 87 octane and cheap copper plugs. 18 mpg average.
Good, I'm a six cyl engine fan. I use to race them against BB v8's on roundy round and clean up. Of course they weren't stock but neither were the v8's.
 

MOAK

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Advocate II

2,923
Wernersville, PA, USA
First Name
Donald
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Diehl
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0745

Fair enough! But, there must have been some other factor, because there certainly isn't anywhere near 30% more energy in pure gasoline than blended fuels, and knock resistance is the same regardless if blended status. Are you sure you arent comparing 91+ pure gasoline to 87 octane ethanol? The additional knock resistance of using 91, with an ECU designed to adjust timing advance in real time, certainly could make the differences you have seen.
True, which is why it surprised me as well.. I tested it on a trip to Ohio with pure regular 87 octane. On the way back ethanol blend 10% 87 octane.. 342 miles each way. Carried an extra 10 gallons to make it there as the range is 250 miles.. daughter is a solid state chemist, it made no sense to her either
 
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Lanlubber

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Mimbres, NM, USA
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True, which is why it surprised me as well.. I tested it on a trip to Ohio with pure regular 87 octane. On the way back ethanol blend 10% 87 octane.. 342 miles each way. Carried an extra 10 gallons to make it there as the range is 250 miles.. daughter is a solid state chemist, it made no sense to her either
Are you driving an LRD2 ?
 

MOAK

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Wernersville, PA, USA
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Donald
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Diehl
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Are you driving an LRD2 ?
No, that test was done about 10 years ago with a Jeep Rubicon.. I’ve yet to do any studies with my 80 series LC but after 6 years I’m going to start.. easy math actually 2.7 per gallon divided by 13mpg is 20 cents per mile.. 3.2 - 16mpg = 20 cents per mile , so in order to make premiium worth while I’d have to crack 17 mpg.
 
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Biker Eagle

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Enthusiast I

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Chelsea, AL, USA
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Anecdotal evidence, last 10 days in Tennessee traveling 1800 miles. Average of 10% ethanol 87 0ctane($2.29 per gal)...17.1mpg. Average of 10% ethanol 93 octane($2.77 per gal)...18.4mpg. Average of 100% pure gas 87 octane($2.52 per gal)...19.0mpg. All miles in my GX470 on the interstate with cruise set at 70mph.
 
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Lanlubber

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Influencer I

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Mimbres, NM, USA
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Ham Callsign
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Anecdotal evidence, last 10 days in Tennessee traveling 1800 miles. Average of 10% ethanol 87 0ctane($2.29 per gal)...17.1mpg. Average of 10% ethanol 93 octane($2.77 per gal)...18.4mpg. Average of 100% pure gas 87 octane($2.52 per gal)...19.0mpg. All miles in my GX470 on the interstate with cruise set at 70mph.
Good info, I only wish our gas was that cheap here in rural NM. It's $0.30 a gal cheaper 60 miles away on an interstate highway. Takes me 7 gallons to drive there and back so it's not worth the drive for cheap gas prices. Do you consider pure gas as a premium grade ? 87 octane isn't that high but if it's considered premium I could use it in my LRD2. There is only one service station in town that carries the pure gas. Thanks again, Lanlubber