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POLL: 87, 89, 91?


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I will run any octane of ethanol-free gas before I'll put 10% ethanol blend in. QT stations around here mostly all have the 87 octane ethanol-free for $2.95 and I get - you guessed it - 10% better mileage when I'm running 100% gasoline. I have not noticed any difference in power going from lower to higher octane. I don't think our engines have enough compression to really need higher octane gas. When I was in Durango Colorado a couple of years ago, I was running 85 octane gas the whole time and got great performance out of it in the 8500-11000 foot elevations.
 

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If the engine pings on 87, then a higher octane fuel may give better performance. However, if this is an OE engine, then there is something wrong with it. If the compression has been increased or the timing artificially advanced, then the engine may need higher octane to take advantage of the modification.
 

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I will run any octane of ethanol-free gas before I'll put 10% ethanol blend in. QT stations around here mostly all have the 87 octane ethanol-free for $2.95 and I get - you guessed it - 10% better mileage when I'm running 100% gasoline. I have not noticed any difference in power going from lower to higher octane. I don't think our engines have enough compression to really need higher octane gas. When I was in Durango Colorado a couple of years ago, I was running 85 octane gas the whole time and got great performance out of it in the 8500-11000 foot elevations.
The higher the altitude, the lower the required octane.

Dave
 

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If the engine pings on 87, then a higher octane fuel may give better performance. However, if this is an OE engine, then there is something wrong with it. If the compression has been increased or the timing artificially advanced, then the engine may need higher octane to take advantage of the modification.
On our engines you will probably not ever hear ping because the knock detection system is working. If the engine is knocking slightly (incipient knock, not readily audible), the system is sensitive enough to detect it and will retard the ignition timing, which reduces performance and raises the exhaust temp. So you might benefit slightly form higher Octane fuel even if you can't easily sense the difference in performance or fuel economy. The worst-case for engine knock is hot and dry ambient and high baro.

Dave
 

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I haven't tried ethanol free gas since my last Civic... Which also got 10% better mileage when burning ethanol free. It became unavailable at the pumps in my area for several years, when it came back it was only 87 and I was in cars requiring 91+. I haven't been brave enough to try 87 puregas in a vehicle requiring 91 yet but I may soon now that the seed has been planted.
 

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I haven't tried ethanol free gas since my last Civic... Which also got 10% better mileage when burning ethanol free. It became unavailable at the pumps in my area for several years, when it came back it was only 87 and I was in cars requiring 91+. I haven't been brave enough to try 87 puregas in a vehicle requiring 91 yet but I may soon now that the seed has been planted.
You can expect 3% better fuel mileage with Ethanol free because it has 3% more energy per gallon
 

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Found out last night that several stations in my town now dispense ethanol free 90. Filled up last night, half 93 E10 and half 90 E0. I want to say I can feel a difference but it's also cooler right now... Could just be a placebo. We'll see if the fuel economy changes.
 

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You can expect 3% better fuel mileage with Ethanol free because it has 3% more energy per gallon
You can expect exactly 10% better gas mileage because there is exactly 10% more GAS in your tank. The alcohol doesn't do a damned thing to help the car go forward.

I've kept a detailed spreadsheet of every tank of gas I have put in my car for 5 years like religion. Without any shadow of a doubt, I got 10% better mileage, different octanes had zero effect.

Here's a bit of the accumulated data:

Avg MPG
28.11
Total Fuel $
$4,675.54
Miles Driven
48,117.48
Cost per Mile
$0.70
Total Gallons
1716.44
Avg Cost/gal.
$2.73
Repair/upgrades
$8,244.55
 

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You can expect exactly 10% better gas mileage because there is exactly 10% more GAS in your tank. The alcohol doesn't do a damned thing to help the car go forward....

Sounds like your car just doesn't run very well on E10. Ethanol works perfectly well as a fuel by itself, as long as the engine is tuned for it.
 

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I wonder why I would bother tuning a car to run alcohol when I have gasoline readily available? That shit does not belong in a gas tank, period.

It actually runs fine on E10, it certainly doesn't complain or seem to have a lack of power... it just doesn't go as FAR. That's really the bottom line.
 

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Numbers don't lie. I have mapped every tank of gas and noted the results. It's 10% better mileage no matter how I drive it.

Yes, alcohol burns and you get a tiny amount of energy from it.

Try lighting a bonfire with alcohol. Then try again with gasoline.
 

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According to the US Dept of Energy, "1 gallon of E10 has 96.7% of the energy of 1 gallon gallon of gasoline." This doesn't really go into the details of octane ratings or how quickly (or slowly) ethanol burns in relation to pure gasoline. Ethanol by itself has an octane rating of 110. I'm no chemist, but I believe that means your 87 octane E10 can be a mixture of 90% ~84.5 octane gasoline and 10% 110 octane ethanol. (84.5*0.9)+(110*0.1)=87.05. This would certainly make life easier on refineries to meet the standard numbers.
Since ethanol was not added to gasoline in the US market until at least 2005, our cars weren't really tuned to this specific fuel type. Hence why older cars (with stock engine management) may seem to suffer a greater economy loss than even the 3.3% energy density loss.
Again, I'm no chemist or engineer... I did do research on the numbers I provided here but the rest is my own speculation.
 

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I wonder why I would bother tuning a car to run alcohol when I have gasoline readily available?
Well, good question. Not everyone has gasoline readily available, or at least not at a reasonable price. Gasoline has to be made from petroleum, but anyone can make ethanol. If you lived in a land that had no oil and was under embargo, then ethanol might look pretty good.

Also, ethanol is an octane booster. That means that it can lower the price of fuel by utilizing a lower grade of gasoline.
 
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