Octane is basically anti-knock compounds added to the fuel, so the 93 blend still will provide better knock reduction. But, I routinely get 3-4 less mpg with the 10% blends.

 

I've usually run Marathon 93, My bike has developed a ping in the last couple weeks. Switched to (Sorry about the spelling) Sunuko 93 with 10% ethanal, ping seems to have quit.

 

Ethanol has a higher octane rating than gasoline. Pure ethanol really isn't pure: ethanol is defined as 95% grain alcohol with 5% gasoline.

The octane rating of ethanol is 117.

Gasoline basically comes in two octane ratings; 87 and 93. There are areas of the country that get 85 octane and when it is blended with ethanol @ 10% it raises the octane rating to 87.

Most areas that I am familiar with receive 87 octane and add ethanol @ 10% resulting in 89 octane. 91 octane is 93 premium blended with 87 octane to provide a cost savings to the store while still offering a higher octane for those that need the anti-knock properties higher octanes provide.

If you have an engine that will not knock on 89 octane you can use 87 octane with ethanol because it is the same exact product for usually $0.10 less per gallon.

Some stations, but not many, add 10% ethanol to their premuim resulting in a 95/96 octane blend but most stations will have their premium 'cooled down' to 93 octane with the addition of 87 octane to the blend.

Now if you are all thoroughly confused my work is done here, lol.

 

I agree that methanol has a higher octane rating, but it also has a lesser BTU equivalent than gasoline, thus lower mileage.

 

Octane deals with combustion, the higher the octane number the higher the detonation temp. BTU deals with the amount of energy (heat) contained in a molecule. Grain alcohol (the primary ingredient in ethanol) does have less energy (heat) than gasoline, it also has no lubricity characteristics (very bad for moving parts).

I can't personally note any difference in fuel mileage using gas/ethanol 90/10 blend vs using 100% gasoline but my mileage varies so greatly on where I ride, in town, country roads and, highway from less than thirty mpg in town to 50.7 on my last 300 mile road trip running 80 mph av. I just buy gas when I need it and don't fret about it being gas or gas/ethanol blended.

Even if a person could get consistent fuel mileage, say 40 m.p.g. as an example; the introduction of a 10% ethanol blend could only result in a reduction of 10% fuel mileage or in this example, 4 m.p.g. if ethanol contained no (0) energy.

Since ethanol <75,700 Btu/gallon> does have a BTU rating only slightly lower than gasoline <115,000 Btu/gallon>
a gasoline/ethanol (90/10 blend) contains 111,070 Btu. The resulting fuel mileage reduction should be (mathematically) less than one mile per gallon or 0.9825 mpg.
Cheers,

 

You present some interesting facts and as you say, Octane is only important to prevent detonation/knock/pinging. As yes, Ethanol does have a BTU equivalency of 68% of that of gasoline. Using your rational, I routinely get an average of 42mpg, sometimes much higher, sometimes just a bit lower, but using the average, and multiplying the 42mpg by the 10% ethanol content equal 4.2 then multiply by 32%, equates to a reduction of 1.26 mpg, and if using a baseline of 50 mpg, the reduction would be 1.6 mpg. In any event, I dont think I am that far off the mark when saying that I get 3 - 4 mpg less with ethanol blended fuels.

Disclaimer: This experience is my own and may not be replicated by others unless they are as **** about tracking mileage as I am.

 

I have noticed a net loss of 10% using the gas in the maryland area... seems all the stations are selling 87,89 & 93 with 10% etho

 

The biggest problem I've had with E10 fuel is when it absorbes water the ethanol water mixture separates from the gas and lays on the bottom of the tank. Ethanol and water mixture is very corrosive to tanks and fuel system parts. Its never been a problem in my bike because it doesn't stay in the tank long. My other motors that get layed up for a couple of months have all had problem especially my boat. I now go ethanol free stations for my mowers and boat.

 

I get 3-4 mpg less on my GMC pickup with the 323 V8. I have checked it over and over, and it is consistently lower vs gas with no ethanol. I ride my bike so much, and the gas mileage is so good, it doesn't bother me anyway.

 

In my part of the country the stations that cater to boaters purchase 100% gasoline for their 93 octane pumps to avoid the very real problem you face. If you frequent a station near the lake or river or ocean in your area ask them if they would/could sell pure gasoline for marine use or they may already do so.