Is it true E85 octane is not 105, it is 94-96(R+M)/2?
08-07-2010, 11:41 PM
#1
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Is it true E85 octane is not 105, it is 94-96(R+M)/2? According to Wikipedia, E85 is not 105 like everyone says. It is actually barely higher than premium 93 octane. So how is everyone claiming to be able to get a much higher compressed engine or be able to add timing with E85 if it is barely higher in octane rating?
http://en.wikipedia.org/wiki/E85
"E85 has an octane rating higher than that of regular gasoline's typical rating of 87, or premium gasoline's 91-93. This allows it to be used in higher compression engines which tend to produce more power per unit of displacement than their gasoline counterparts. The Renewable Fuels Foundation states in its Changes in Gasoline IV manual, "There is no requirement to post octane on an E85 dispenser. If a retailer chooses to post octane, they should be aware that the often cited 105 octane is incorrect. This number was derived by using ethanol’s blending octane value in gasoline. This is not the proper way to calculate the octane of E85. Ethanol’s true octane value should be used to calculate E85’s octane value. This results in an octane range of 94-96 (R+M)/2. These calculations have been confirmed by actual octane engine tests."
http://en.wikipedia.org/wiki/E85
"E85 has an octane rating higher than that of regular gasoline's typical rating of 87, or premium gasoline's 91-93. This allows it to be used in higher compression engines which tend to produce more power per unit of displacement than their gasoline counterparts. The Renewable Fuels Foundation states in its Changes in Gasoline IV manual, "There is no requirement to post octane on an E85 dispenser. If a retailer chooses to post octane, they should be aware that the often cited 105 octane is incorrect. This number was derived by using ethanol’s blending octane value in gasoline. This is not the proper way to calculate the octane of E85. Ethanol’s true octane value should be used to calculate E85’s octane value. This results in an octane range of 94-96 (R+M)/2. These calculations have been confirmed by actual octane engine tests."
08-07-2010, 11:55 PM
#2
Because of the R+M side of the formula.
E85 is highly resistant to knock but somewhat sensitive to preignition. The sensitivity of preignition is what causes the actual octane rating to go down.
E85 is highly resistant to knock but somewhat sensitive to preignition. The sensitivity of preignition is what causes the actual octane rating to go down.
08-08-2010, 12:59 AM
#4
i dont really think it matters what the actual/theorized/believed octane rating is. there's guys running 16:1 compression on pump e85 so that kinda blows the traditional train of thought about octane out of the water. the benefits i see are cooler IATs and operating temps, more power, wider tuning window, and its CHEAP compared to the leaded 110 octane race gas of your choice. your typical streep/strip motor can run 13:1 no problem and thats traditional SBCs running carbs.
