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  1. #1
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    Guide to Measuring E85 Content in Fuel and Calculators to Determine Mixes

    Guide to Measuring E85 Content in Fuel and Calculators to Determine Mixes

    With so many folks running some mixture of E85, I thought it would be a good idea if we have a how to guide here for measuring the content of ethanol in our gas. In addition, I thought it helpful to have a simple excel calculator that could quickly determine the amount of gas we should add to a tank of gas to hit a desired level of ethanol mix.

    What’s in Our Tanks Anyways?
    Pump gas usually consists of a small percent of alcohol/ethanol depending on brand, location and season, hence all the warnings that your pump fuel may contain up to 10% ethanol (federally approved to increase to 15% in the future). E85 is supposed to be 85% ethanol and 15% gas, but like regular pump gas, can have its ethanol content vary between winter and summer based on the manufacturers’ mix.

    As such, it’s always important to know what percentage of ethanol is in your tank (unless you have a fancy flex fuel system, of which I have zero knowledge on how accurate these are).

    Why is this important?
    Running incorrect boost, timing and AFRs on your tune for the gas in your tank can destroy things you love, like your engine, puppies and baby pigs.

    For example, here are some logs I had when I mixed up a tank of what should have been E30 on the Cobb E30 OTS maps. The timing drops made me pretty unhappy. I am sure that the “E85” I bought was actually 85% devils blood and not the promised turbo nectar of the Gods.

    Click here to enlarge

    How to Measure E85
    It’s not too hard to find instruction on measuring content of ethanol on the web, but most are all over the place on the examples and I wanted to provide a little more easy-to-use excel file to calculate the ethanol contact.

    For those curious, the basic concept is that if you combine water with E85 (or any combination of gas and alcohol/ethanol), the water and alcohol/ethanol will mix together and the gas will separate. Based on the amount of gas that separates, you can do the math to determine the percent of the fuel that was alcohol/ethanol.

    What’s In the Excel File?

    MACROS!!!! (See below)

    The first table is used to measure the content of ethanol based on a sample of test fuel and water. Simply put a mixture of water and test fuel in a sealable container, then shake and bake (kidding about the bake part, please don’t bake). Let the mixture set for 5-20 minutes until a clear separation can be seen in the fluid, input the measurement of the separation. The formula will output the ethanol content of the test mix.

    The second table will tell you the ethanol content of a tank of gas given the Test Fuel you just tested and a tank of gas.

    The third table, my favorite and most practical, will tell you how much Test Fuel you should add to a tank of gas with a known ethanol content to hit a desired mixed ethanol content. Notes, we need the macros here to complete this calculation because as we add more fuel to the current tank, the calculation changes. Math is crazy.

    See attaached

    Here’s a good tool for checking octane. I have noticed that if you use factions of gallons the calculations act weird and don’t compute per my math, so I would suggest using whole numbers. You will notice that my file doesn’t give a $#@! if you use decimal, it’s always happy to serve us humans.

    http://www.intercepteft.com/calc.html
    Attached Files Attached Files
    Last edited by mithiral67; 01-30-2013 at 10:06 PM.
    2015 - Cayman GTS - Stock
    2011 - 335is e92 - Cobb PTF E40/Rob Beck/AR/Helix (458 rwtq and 479 rwhp) - Retired
    2007 - 911 Turbo - EP1/AMS (617 awtq and 500 awhp) - Retired
    2008 - 335i e92 - Cobb/AR/Helix/OSS (384 rwtq and 356 rwhp) - Retired
    2003 and 2005 330i/ci zhp - Stock - Retired

  2. #2
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    Moved to general automotive.

  3. #3
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    I like it better when you are "occupied" and threads sit where I put them.
    2015 - Cayman GTS - Stock
    2011 - 335is e92 - Cobb PTF E40/Rob Beck/AR/Helix (458 rwtq and 479 rwhp) - Retired
    2007 - 911 Turbo - EP1/AMS (617 awtq and 500 awhp) - Retired
    2008 - 335i e92 - Cobb/AR/Helix/OSS (384 rwtq and 356 rwhp) - Retired
    2003 and 2005 330i/ci zhp - Stock - Retired

  4. #4
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    Click here to enlarge Originally Posted by mithiral67 Click here to enlarge
    I like it better when you are "occupied" and threads sit where I put them.
    I like it better when they are where I want them.

  5. #5
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    Photo of my test kit. Picked it up at a chem shop.
    Attached Images Attached Images  
    2015 - Cayman GTS - Stock
    2011 - 335is e92 - Cobb PTF E40/Rob Beck/AR/Helix (458 rwtq and 479 rwhp) - Retired
    2007 - 911 Turbo - EP1/AMS (617 awtq and 500 awhp) - Retired
    2008 - 335i e92 - Cobb/AR/Helix/OSS (384 rwtq and 356 rwhp) - Retired
    2003 and 2005 330i/ci zhp - Stock - Retired

  6. #6
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    Very cool James,

    Click here to enlarge
    PTF PROTuned | RB's | AMS FMIC | AR DP's | HPF Exhaust | CP-E DCI | Apex Arc 8's | 235/275 Star Specs |

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  7. #7
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    FYI, for $20 shipped you can get this. http://www.summitracing.com/parts/qft-36-e85/overview/

    Only downside is it only measures ethanol content between E70-E100. Credit to @rader1 for sharing this.
    2011 E90 M3 \ Melbourne Rot Metallic

    Click here to enlarge

  8. #8
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    Nice kit. I wanted a small funnel and a turkey bauster to be precise. Was $25 all in for my set up.
    Now to cool some meth to pay for it.
    2015 - Cayman GTS - Stock
    2011 - 335is e92 - Cobb PTF E40/Rob Beck/AR/Helix (458 rwtq and 479 rwhp) - Retired
    2007 - 911 Turbo - EP1/AMS (617 awtq and 500 awhp) - Retired
    2008 - 335i e92 - Cobb/AR/Helix/OSS (384 rwtq and 356 rwhp) - Retired
    2003 and 2005 330i/ci zhp - Stock - Retired

  9. #9
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    Yes Reputation No
    Bump for folks from the other forum to find.
    2015 - Cayman GTS - Stock
    2011 - 335is e92 - Cobb PTF E40/Rob Beck/AR/Helix (458 rwtq and 479 rwhp) - Retired
    2007 - 911 Turbo - EP1/AMS (617 awtq and 500 awhp) - Retired
    2008 - 335i e92 - Cobb/AR/Helix/OSS (384 rwtq and 356 rwhp) - Retired
    2003 and 2005 330i/ci zhp - Stock - Retired

  10. #10
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    ps, The title is wrong, should be ethonal in fuel, but i wanted E85 in the title to hook the viewers.
    2015 - Cayman GTS - Stock
    2011 - 335is e92 - Cobb PTF E40/Rob Beck/AR/Helix (458 rwtq and 479 rwhp) - Retired
    2007 - 911 Turbo - EP1/AMS (617 awtq and 500 awhp) - Retired
    2008 - 335i e92 - Cobb/AR/Helix/OSS (384 rwtq and 356 rwhp) - Retired
    2003 and 2005 330i/ci zhp - Stock - Retired

  11. #11
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    Click here to enlarge Originally Posted by mithiral67 Click here to enlarge
    ps, The title is wrong, should be ethonal in fuel, but i wanted E85 in the title to hook the viewers.
    That's fine always think about what is best for views or SEO.

    Stage 2 or 2.5 E9X M3 S65 V8 supercharger kit for sale
    : http://www.boostaddict.com/showthrea...r-kit-for-sale

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