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  1. #1

    Mixing fuel to get 93 octane

    Oklahoma has dropped 93 octane from the pumps. I can get 86, 88 and 91. And can NEVER find 91 on the water without paying a small fortune for it.
    I have about 45 gallons of 110 from Spring and will need to blend my own to get to 93 octane.

    But I have a couple of questions. Will 110 and 91 stratify if left sitting for a month or so? Does anyone have an online ration calculator thats easy to use to see how much 110 I need to put into X amount of fuel at X octane to achieve 93?

    And do I really even need to worry about getting to 93 or is 91 sufficient for stock 300PM's?

    According to my math, for every 10 gal of 87, I will need to add 3.5 gal of 110. Does that sound correct?

    I would have to trailer the boat and take it to town to get 91 octane, which would be cheaper in the long run because of having to use LESS of the $9/gal 110 octane.
    I could get 100LL for $5.78 at our airport but I'm not sure if you can mix it with 91!

    Any advice on getting to 93 from 87 or 91?!
    Last edited by waterboy222; 07-27-2011 at 12:43 PM.
    24 Skater w/ 300 Promaxes "99 Problems"

  2. #2
    I mix the racing fuel with 93 ethanol gas all the time and haven't had any separation problems but I just do it incase I get a tankfull of gas that might not really be 93 octane. I only add 1 or 2 gallons of C12 to 10 gallons of 93 to act as a cushion for crappy gas. Been doin it for about 2 years and no problems yet with 155 lbs of compression.

  3. #3
    Will there be any issues if I overshoot the octane and end up with 98oct or higher? Will avgas kill the lubricity of the oil?!
    24 Skater w/ 300 Promaxes "99 Problems"

  4. #4
    Join Date
    Aug 2007
    Location
    North Eastern North Carolina
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    6,646
    Try this formula. I believe it was posted by H2OSkier a month or so ago.
    1. (Octane of fuel #1) X (# of gallons of fuel #1) = X
    2. (Octane of fuel #2) X (# of gallons of fuel #2) = Y
    3. X + Y = Z
    4. Dividing Z by the total number of gallons of both fuels gives you your total octane number.

    For example, let's say you have 10 gallons of 93 octane, and 5 gallons of 112 octane race gas.

    1. 93 X 10 = 930
    2. 112 X 5 = 560
    3. 930 + 560 = 1490
    4. 1490 / 15 = 99.33

    So, the total octane of the mixture would be just over 99.

    In yiour case it looks like 10 gals of 91 to 1.5 gals of 110 will yield 93.5 ish

    Last edited by HStream1; 07-27-2011 at 01:05 PM.
    Bud Conner "Heathen Supporting Our Constitution"

    FOR ALL ENGINE APPLICATIONS
    DRY Film Lubricant for Piston Skirts & Cranks + Thermal Barrier Ceramic Coatings for Piston Tops, Combustion Chambers, Valves etc !!


    Banner Compliments of Pete Woodworth!!!




  5. #5
    Here is the octane calculator http://www.motorsportsracingfuels.co...alculator.html I use 100LL to mix with 91 to get 93. The manual for the merc 280 says that if you use leaded gas you might get some lead buildup in the exhaust but it's okay to use. I even carry a few gallons of straight avgas with me in the boat incase I run low on gas and have to buy 89 octane marina gas. I've been told that the avgas may have anti-icing agents added to it's blend in the winter months so you might want to check with the airport during those times of years and you might want to make sure leaded gas is okay in your engine. I also use the avgas blend in my snowmobile in the winter time. My airport even sells 91 octane lead free, ethanol free gas. They started selling it this summer for the musclecar, motorcycle, snowmobile crowd. Wish it was 93 octane, as it would save me mixing it.

  6. #6
    Thanks for the help guys! This is pretty interesting.. I ran 4 calculations to see what the most efficient means to get 93 would be. All these numbers are based on a final quantity of 40 gal of 93 oct.
    87 oct + 100LL AVGAS = $187.98 of 93 oct
    91 oct + 100LL AVGAS = $171.17 of 93 oct
    91 oct + 110Race Fuel = $176.47 of 93 oct
    87 oct + 110Race Fuel = $209.64 of 93 oct

    So to get 40 gal of 93 octane, the cheapest means would be to buy 31.1 gal of 91 Premium ($3.85/Gal) at the pump in town and cut it with 8.9 gal of 100LLAVGAS ($5.78/gal) from the airport.

    Thanks for the help! I was going to mix 87 and 110. To mix it correctly and end up with 40 gal in each tank, I would have spent $136.94 MORE than using 91 and 100LL

    Thanks!!
    24 Skater w/ 300 Promaxes "99 Problems"

  7. #7
    Join Date
    Jul 2003
    Location
    Discovery Bay, CA
    Posts
    873
    I always cut my unleaded 91 w/ 20% 110 leaded race fuel on my 280 and never had a problem over 7 years of owning it. I also kept it stock and never raised the rev limiter past 8,200........

  8. #8
    Join Date
    Aug 2007
    Location
    North Eastern North Carolina
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    6,646
    Just out of currosity? (And it's your money no matter how you slice it and dice it. But?

    How do you come up with $136.04 difference based on the numbers you show below? I fail to see the spread that equates to $136.04.


    Quote Originally Posted by waterboy222 View Post
    Thanks for the help guys! This is pretty interesting.. I ran 4 calculations to see what the most efficient means to get 93 would be. All these numbers are based on a final quantity of 40 gal of 93 oct.
    87 oct + 100LL AVGAS = $187.98 of 93 oct
    91 oct + 100LL AVGAS = $171.17 of 93 oct
    91 oct + 110Race Fuel = $176.47 of 93 oct
    87 oct + 110Race Fuel = $209.64 of 93 oct

    So to get 40 gal of 93 octane, the cheapest means would be to buy 31.1 gal of 91 Premium ($3.85/Gal) at the pump in town and cut it with 8.9 gal of 100LLAVGAS ($5.78/gal) from the airport.

    Thanks for the help! I was going to mix 87 and 110. To mix it correctly and end up with 40 gal in each tank, I would have spent $136.94 MORE than using 91 and 100LL

    Thanks!!
    Bud Conner "Heathen Supporting Our Constitution"

    FOR ALL ENGINE APPLICATIONS
    DRY Film Lubricant for Piston Skirts & Cranks + Thermal Barrier Ceramic Coatings for Piston Tops, Combustion Chambers, Valves etc !!


    Banner Compliments of Pete Woodworth!!!




  9. #9
    I am interested in trying this but have a question about the 91 or 93 octane fuel. Is the 91 octane with ethanol or without and does it matter?

  10. #10
    Join Date
    Aug 2007
    Location
    North Eastern North Carolina
    Posts
    6,646
    Most all fuels have ethanol now days unles stated otherwise. But to answer your question no it doesn't matter.
    Bud Conner "Heathen Supporting Our Constitution"

    FOR ALL ENGINE APPLICATIONS
    DRY Film Lubricant for Piston Skirts & Cranks + Thermal Barrier Ceramic Coatings for Piston Tops, Combustion Chambers, Valves etc !!


    Banner Compliments of Pete Woodworth!!!




  11. #11
    HStream1,
    Thanks for the clarification. Luckily for me I have a fleet fuel sales place about 30 minutes from me that sells 90 NON Ethanol in the summer and 93 NON-ethanol in the winter at reasonable prices.
    But the local SUNOCO is right down the street for corn juice.
    Last edited by dcarter; 07-28-2011 at 08:18 AM.

  12. #12
    Join Date
    Sep 2008
    Location
    Treasure Island Fl
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    1,107
    Quote Originally Posted by waterboy222 View Post
    Will there be any issues if I overshoot the octane and end up with 98oct or higher? Will avgas kill the lubricity of the oil?!
    I would like to know this as well. It has haunted me ever since I scored a piston running a high dose of 110 race fuel mixed with 89 oct. Not sure if it had anything to do with the race gas. It was a strong motor with perfect compression @ 120 psi. I was at WFO for a while when it happened. It was the first time I had tried the witches brew. I added a lot of race gas bc I wanted to be on the safe side and we were going on a run where I knew I would be at wfo for extended periods. Does it reduce the lubrication???
    Cawley

  13. #13
    Quote Originally Posted by HStream1 View Post
    Just out of currosity? (And it's your money no matter how you slice it and dice it. But?

    How do you come up with $136.04 difference based on the numbers you show below? I fail to see the spread that equates to $136.04.
    Youre right, Im not sure where that $136.04 came from, fat fingers on a small calculator I assume. It would actually be $76.94 in savings over 80 gal.
    Thanks for the catching that!
    24 Skater w/ 300 Promaxes "99 Problems"

  14. #14
    Quote Originally Posted by native2 View Post
    Does it reduce the lubrication???
    Ive heard that racegas doesn't cut lubricity but avgas does. But I'd sure like for an expert to throw in his opinion!
    24 Skater w/ 300 Promaxes "99 Problems"

  15. #15
    Av gas does not have the lubricating ability as pump gas, but you can just add a small amout of good oil to how ever much av gas you use in your blend. I ran straight av gas mixed with 50-1 xd 50 in my Monty v-8 for over a year with no problems. And I hate to bring bring back the cotroversy, but a lot of people have sucessfully used ACES in situations like yours.

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