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Default <e85 = lower octane? - 08-18-2014, 07:29 AM

Hi all - I did a Google search and didn't find an answer so thot I'd post this question: Does an ethanol content less than 85 mean an octane less than 105? For example, if I test my local e85 and find it is really e80 or even e70 (some pumps in the area indicate e70 is the min content, tho Ive never tested anything this low) does that mean an octane less then 105?
Thanks!


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PR3CI5N335i PR3CI5N335i is offline
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Default 08-18-2014, 08:35 AM

Yes the less Ethanol the lower the octane.. E60 is about 100oct
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Default 08-18-2014, 09:18 AM

Quote:
Originally Posted by PR3CI5N335i
Yes the less Ethanol the lower the octane.. E60 is about 100oct
Hi and thanks-So I understand that if I mix e85 with 91 (in your example of e60) it yields something lower but my question was more about the e85 manufacturing process, if that makes sense. So if the e85 producer makes a batch of e80 and delivers that to the station, then right out of the pump is that e80 slightly lower in octane than e85 OR does the manufacturer try to maintain the 105 octane rating even if what they produced is e80 or e70...


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Default 08-18-2014, 11:03 AM

Found this: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."


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Default 08-18-2014, 01:59 PM

Last comment and then I'll let it drop
I guess the proof is in the puddin, so to speak. Regardless of it's R+M/2 rating, it clearly is a hugely better fuel than 91 pump. All us hotrodders can't be wrong
With a special thanks to my buddy for showing me the error of my ways.


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Default 08-18-2014, 02:58 PM

You will definitely see a difference in timing using a typical winter E70 blend compared to a summer E85 mix.
A little 87 octane mixed with the ethanol dose hurt the octane a lot.


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Default 08-18-2014, 06:33 PM

I think Robert is hooked and we're going to be seeing a lot of him!

Robert, I wouldn't sweat small percentages. The more you get to know your car, the more you'll notice slight differences in fuel quality, performance, and so on. Test, log, review...

If you do those 3 simple things and the car is happy...



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Default 08-18-2014, 07:35 PM

The R+M/2 method doesn't take into account the benefits of alcohol in the combustion process. Although e85 has an r+m/2 octane of 96 it is about as knock resistant as 105 octane gasoline
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Default 08-18-2014, 08:34 PM

Quote:
Originally Posted by noorj
The R+M/2 method doesn't take into account the benefits of alcohol in the combustion process. Although e85 has an r+m/2 octane of 96 it is about as knock resistant as 105 octane gasoline
Yep. And someone else showed me a test where a highly tuned engine was dyno'd with 100 oct gas and e85 and the power output was the same (e85 actually slightly higher output)


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