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Ethanol is used in racing engines.
Ethanol increases HP.
Pure ethanol is 113 on the octane scale.
Actually ethanol does not increase HP. It allows for a higher compression which does increase power output of the engine. The compression is to low on engines running gasoline therefore there is less power output from having ethanol in the gasoline. See the wiki quote below.

"Ethanol contains approximately 34% less energy per unit volume than gasoline, and therefore in theory, burning pure ethanol in a vehicle reduces range per unit measure by 34%, given the same fuel economy, compared to burning pure gasoline. However, since ethanol has a higher octane rating, the engine can be made more efficient by raising its compression ratio."

 

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Sonwon, you're talking about higher octane but that's not what jdock is referring to. Ethanol gives power to an unmodified engine because it adds oxygen. It only needs a richer AFR to make up for the lesser amount of pure hydrocarbons that it displaces. Same is true for any oxygenant. It looks like a stock Rebel does run rich enough up thru the mid range according the measured AFR. Most bikes are a little rich at full throttle and might see the same benefit. If fueling isn't rich enough, E0 would make more power.
 

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Sonwon, you're talking about higher octane but that's not what jdock is referring to. Ethanol gives power to an unmodified engine because it adds oxygen. It only needs a richer AFR to make up for the lesser amount of pure hydrocarbons that it displaces. Same is true for any oxygenant. It looks like a stock Rebel does run rich enough up thru the mid range according the measured AFR. Most bikes are a little rich at full throttle and might see the same benefit. If fueling isn't rich enough, E0 would make more power.
Thank you for the clarification, in my defense nowhere was oxygenanted mentioned. And as you pointed out this relies on a rich fuel mixture which was also not mentioned. I suppose if it is rich enough it could work however modern engines are designed to run lean to reduce emissions. I doubt the Rebel 500 would be rich enough to benefit from E10. I admit I have never seen a fuel map for a stock Rebel 500. Do you have one?

In personal test in cars E0 tends to provide a little better fuel mileage. I run E5 in an 1100 since the E0 is more than double the price and is very hard to find. I know my Sportster runs better with E5 than E10. E10 gave it this odd stumble when really hot, likely a problem with air cooling over water cooling, the ECM didn't properly adjust to E10, just the fact E10 burns hotter, or all of the above. The E10 did meet the knock requirements of the Sportster. I also like having a little less corrosion water sucking fuel in the tank so I use E5 in all my bikes.
 

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The O2 sensor is used to control AFR at idle and cruise automatically so that gets adjusted to around 14.2:1 for E10. As revs go up and loads increase, manufacturers tend to keep things pretty much on the increasingly too rich side. That's according to various dyno charts that show AFR. What I'd like to know is the ethanol content used. Here's one for the CB500:
Rectangle Slope Font Line Plot
 
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