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Discussion Starter · #1 ·
Ok here is the deal!!!

I have been reading about the whole higher octane fuel and better mileage blah blah blah....

In Canada we have 10% ethanol in our 87 octane, our 89 octane only has 5% ethanol so we know that 89 octane will get better mileage cause it has less ethanol.

I would like to use my car as an example. I get 35mpg as a baseline average for mileage.

I have been using 87 octane which costs 4.69/gallon currently and costs me $0.134/mile.

89 octane costs $4.88/gallon. I have calcualted that if my car were to get 2 more mpg on 89 octane it would only cost $0.131/mile.

Now the million dollar question is can you get 2+ more mpg on 89 octane vs 87 octane or rather can my eco get 37mpg on 89 octane.

Discuss :)
 

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...you only have to exceed 36.4 mpg to make the $4.88/gal cost of 89 octane worth your while! Here's the equation:

X(mpg)/35(mpg) = $4.88(89)/$4.69(87)

X(mpg) = 35(mpg)*[$4.88(89)/$4.69(87)] = 36.4(mpg)
 

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Discussion Starter · #3 ·
...you only have to exceed 36.4 mpg to make the $4.88/gal cost of 89 octane worth your while! Here's the equation:

X(mpg)/35(mpg) = $4.88(89)/$4.69(87)

X(mpg) = 35(mpg)*[$4.88(89)/$4.69(87)] = 36.4(mpg)
Ok, nice job on the equation.....now that is established.....can 89 octane give you a 1.5mpg increase without changing any other variables???
 

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Ok, nice job on the equation.....now that is established.....can 89 octane give you a 1.5mpg increase without changing any other variables???
Having mostly used 89 pre-tune, I don't think so, and if so there are way too many variable involved to be able to take on that kind of test. I did notice 89 ran a lot smoother and is probably healthier for the engine (as in the knock sensor doesn't have to worry about saving the engine, and it wont pull any timing to run that 87 crap)
 

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In Minnesota I believe our 89 octane is higher% ethanol; it's the same price as 87. I've gotten better mileage using 87.
 

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Discussion Starter · #6 ·
Our premium is 100% gasoline, but I don't think the added cost is going to make it cost effective, this is why I thought the 89 might be the way to go.....I am hoping there are enough budding scientists/engineers that could provide enough insite into the effects of ethanol on mpg
 

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Ethanol provides less energy per unit volume, and the A/F ratios are not the same, so more ethanol is consumed. Not only that, but it corrodes your engine as well. I have been using exclusively E0 90 Octane fuel in my Eco Cruze M/T and have consistently got 50+ on the highway and usually get in the 30's off highway except when stuck in crazy traffic.

My Fuelly badge is WAY off because my second recorded fill up was half used up from my fiance learning to drive stick (lots of jackrabbits!) and the third fill up filled up the whole tank, passing the Eco M/T restrictions.
 

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Our premium is 100% gasoline, but I don't think the added cost is going to make it cost effective, this is why I thought the 89 might be the way to go.....I am hoping there are enough budding scientists/engineers that could provide enough insite into the effects of ethanol on mpg
While I'm NOT a budding scientist I do think I'm a logical thinker so I would suggest THIS to answer your original question.
1. Run your current tank down
2. Fill with 89 and bite the bullet on the extra $2 +/-.
3. Calculate your new mpg and know EXACTLY what the difference is.
 

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Discussion Starter · #9 ·
While I'm NOT a budding scientist I do think I'm a logical thinker so I would suggest THIS to answer your original question.
1. Run your current tank down
2. Fill with 89 and bite the bullet on the extra $2 +/-.
3. Calculate your new mpg and know EXACTLY what the difference is.

I am so busted.....I was hoping that someone else would bite the bullet and take on the test :D so I wouldn't have too.

I would think you would have to do 3 fillups to make it a nice average to know for sure.
 

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I am so busted.....I was hoping that someone else would bite the bullet and take on the test :D so I wouldn't have too.

I would think you would have to do 3 fillups to make it a nice average to know for sure.
I'm sure one of us here will do it.....................I'm just hoping it won't have to be ME! :eek:
 

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Only way to know is to test it on your normal route. Anyone elses route carries different mix of hills, highway, city, etc.

Also... if your 87 vs. 89 prices change, your tipping point changes. Taking a $0.10 drop in each you get the below. But if they change relative to each other in price, it will be slightly different. So... track the cost difference between them, and your MPG increase (if any) and see.

My guess is you won't see the pay off without a tune, but the cost of the tune drives the payback period out there a ways in miles. If you drive 20,000+ miles a year like I do, payback isn't so bad though.

Code:
MPG     89 Octane   87 Octane       
36.42   4.88           4.69       
36.45   4.78           4.59       
36.48   4.68           4.49       
36.51   4.58           4.39       
36.55   4.48           4.29       
36.59   4.38           4.19       
36.63   4.28           4.09       
36.67   4.18           3.99       
36.71   4.08           3.89       
36.75   3.98           3.79
 

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I would think you would have to do 3 fillups to make it a nice average to know for sure.
...yep, like the old saying goes: "...best two-out-of-three..." (ha,ha).

...the practical reason is to "average" any over-filled tank with its subsequent under-filled tank.
 

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For your information, i'm in Québec, Canada, i have 4600KM on the odometer, i always use 91 octane gasoline, the numbers are always consistent for now, i'll stay with the 91 octane so i can compare within different suppliers (Ultramar, Shell, Harnois, Irving, Esso...) i'll change the engine oil next tuesday for the first time at the dealer, after that, i'll see if there is any changes within different tanks from the same supplier. Then i will test with the 89 octane and 87 octane from that best supplier. Shell have a nitrogen enriched gasoline and i can get 20 Air Miles with the 91 octane fill up compared to 5 Air Miles.... Anybody experienced big changes in efficiency between suppliers?
 

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For your information, i'm in Québec, Canada, i have 4600KM on the odometer, i always use 91 octane gasoline, the numbers are always consistent for now, i'll stay with the 91 octane so i can compare within different suppliers (Ultramar, Shell, Harnois, Irving, Esso...) i'll change the engine oil next tuesday for the first time at the dealer, after that, i'll see if there is any changes within different tanks from the same supplier. Then i will test with the 89 octane and 87 octane from that best supplier. Shell have a nitrogen enriched gasoline and i can get 20 Air Miles with the 91 octane fill up compared to 5 Air Miles.... Anybody experienced big changes in efficiency between suppliers?
I have noticed a decrease on a couple of fillups, but it was too minor to mention.

The issue with MPG vs octane is that in order to truly calculate it, you need to drive the exact same miles, the exact same routes, the exact same speeds, the exact same stops then you need a test average to compare to. If this was automotive testing, it would be 15 tanks, average, then 15 tanks with another octane and average and compare the two. Which means installing a smaller tank HAHAHA)

I have been running 93 for the most part for over a month, do I see any noticeable increase, no. When i drive craze my mpg drops, when I drive conservitively it increases. People have to many variables in there lives when driving to ever be able to calculate the differences, late this day, running early the next, stop at the store this day, construction routing difference the next.

This is why we always try and remove the human element when testing, and its the first thing we look at when there is an error.
 

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LOL, with the Cruze, I fill up about once a month unless I take a trip. SOOO....it is going to take me a while to determine (if I fill up 3 times) if the 89 is better for me or not. I will say that last week I filled up with the 89 for the first time, took a 120 mile trip and the average was 39.9 mpg. The return trip was almost 38mpg. Not sure what the difference was, might have been traffic or whatever. It was not 100% highway travelling, most was in the 55mph range, but traveled thru a couple of small towns where I had to do 35. Some interstate where I was doing about 75. Overall very pleased.
 

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...that's *why* the lawyers make all the GM brochures have the words: Your Milage May Vary (ha,ha).
 

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I just started using the Shell premium. Using today's gas prices in Nova Scotia as a base, there is currently a $.07/L difference in the price between regular and premium. I average a fillup every two weeks, so taking that price difference, the switch will cost me $105.00/year extra. Pocket change really, considering the added benefits of using a higher octane gas, without even taking any potential mpg increases into account. And as Djimbe mentioned above, the extra air miles on a fill up are just an added bonus. All things considered, I think I will be sticking with the premium. It would be different were it a huge increase in price, but it's basically costing me a cup of coffee a week, so it seems to be an easy decision to make.
 

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Ethanol has about 30% less energy output so take the 5% less ethanol, divide that by 3 and you get 1.67% more fuel economy on the lack of ethanol alone...assuming it actually is a 5% difference, which we cannot substantiate. There are some testing devices used by Buschur Racing for them to evaluate the ethanol content of e85 for high performance applications. Maybe you'd like to do some testing with their device to see what the content of the ethanol is per different gasoline product?I don't think it costs much money to buy.

That would give us some empirical data to analyze. Right now it's just guesswork. I'm betting it will be different for different refineries as well so your data will only be valid for each 'brand', at best.
 

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In my state 99% of the stations 87 & 89 octane have 10% ethanol, premium has none & is 100% gas at most stations. I have tried 6 or so fillups with 87-89octane & between the two I can find no difference in my MPG. I do see on fuelly a smaller difference between city & highway driving MPG using 87 or 89, with premium I drop down to regular gas levels(which is a larger swing since I get much better on the highway with premium).

On longer trips with very few stops with premium 100% gas I do see a huge difference in my mpg. best I can get with 10% ethanol is 37mpg. with premium on the same drives with the same driving style I am above 41mpg. Even my girlfriend says the motor sounds nicer with premium & seems to have more power down low(I try to never rev past 4,000rpm).

We both decided that even at 60cents a gallon($6 a tank) the car is so much better on premium thats all we will fill with in the future. Most of the time you can watch prices though & find a station thats only 20cents a gallon more.
 
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