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What uses 85 octane gasoline?

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  • #61
    Originally posted by A.K. Boomer View Post
    In total agreement Willy if you can find premium with less ethanol content it's a total game changer as it's more energy dense,
    Yep, ethanol has less energy per gallon than gasoline but the octane rating has nothing to do with energy density. Using a higher than recommended octane gasoline will give you fewer miles per gallon because the octane retards the ignition of the gasoline in the engine. That's the whole purpose of octane; retard ignition to reduce/eliminate pinging. That's why high performance/compression engines need a higher octane gasoline. If you use a higher octane gasoline to avoid ethanol you may end up with the same or fewer miles per gallon for more expensive gasoline.

    Bottom line: use the octane rating that the manufacturer tells you to use, no more and no less.


    • #62
      Originally posted by pgmrdan View Post
      .... Using a higher than recommended octane gasoline will give you fewer miles per gallon because the octane retards the ignition of the gasoline in the engine. ...
      No! The higher rated Octane ONLY prevents pre-detonation of the fuel caused by the heat of compression - or "dieseling". The spark plug ignites the fuel regardless of the its Octane rating.
      Last edited by Mike Burdick; 07-07-2017, 12:14 PM.


      • #63
        For the most part even though I tried to go for a little shock value on this ()

        im in agreement with Willy, higher octane does not retard the ignition of the gasoline ---- that's still all left up to the ignition timing of the spark plugs --- higher octane just insures that ignition is left up to the spark plugs,,, and not left up to "auto-ignition" due to too high of a compression ratio for the fuel octane that's being used,,,

        if you auto-ignite you lose all control of ignition timing --- in fact whats worse is if the auto-ignition starts on one side of the chamber and then your spark ignition starts at the other ------------------ now you have the recipe for detonation,
        Detonation is Pre-ignitions bigger brother, and he's got mental issues and has done a fair share of prison time - and oh yeah he also owns allot of firearms

        MB beat me to it!


        • #64
          Part of the reason 85 octane is illegal may be that at an octane of 108, you just about cannot add the specified amount of ethanol to gasoline and MAKE 85 octane. I strongly doubt that states make it illegal for any other reason.

          If you have proof otherwise, trot it out where we can see it, or cut the cackle.

          Incidentally, the 85 octane under US requirements, corresponds to something around 89 to 91 octane in the UK, due to the use of an average of the research and motor numbers in the US. It gives a number lower by around 5 points.
          CNC machines only go through the motions


          • #65
            Interesting article on 85:



            • #66
              Here's some excellent reading matter on the subject of gasoline from Chevron, 124 page pdf download that will answer most questions.
              I've had this on file for a while and have found it very informative. I realize that at 124 pages it's not exactly a brief overview however it does cover most bases.


              Generally, three grades of unleaded gasoline with different AKIs are available in the U.S.:
              regular, midgrade, and premium. At sea level, the posted AKI for regular grade is usually 87;
              for midgrade, 89. The AKI of premium grade varies, ranging from 91 to 94.
              The posted AKIs are lower in the Rocky Mountain states. Altitude gasolines have historically provided the same antiknock performance as higher-AKI gasolines at sea level. The
              octane requirement of older-model engines decreases as air pressure (barometric pressure)
              decreases. Barometric pressure is lower at higher elevations.
              Home, down in the valley behind the Red Angus
              Bad Decisions Make Good Stories​

              Location: British Columbia


              • #67
                A quote from the big PDF with application here. It seems to contradict some of the points folks have been trying to put forward:

                "Will premium gasoline give better fuel economy than regular?

                Will one brand of gasoline give better mileage than another?

                Gasolines with higher heating values can improve fuel economy. Mileage differences may
                exist, but they will be small compared to the benefits to be derived from the maintenance
                and driving tips mentioned earlier.

                Traditionally, premium gasoline has had a slightly higher heating value than
                regular, and, thus, provided slightly better
                fuel economy. Its mileage difference, less than 1 percent
                better, is not large enough to offset
                premium’s higher cost. The difference is likely to be
                less or nonexistent between grades of RFG.

                There can be variance in
                heating value between batches of gasoline from the same refinery
                or between brands of gasoline from different refineries because of compositional differences.
                The variance is small, and there is no practical way for the consumer to identify the gasoline
                with a higher heating value "
                CNC machines only go through the motions


                • #68
                  Not to dredge this entire mess back up again but --- I been saying premium was 40 cents higher, was just a guess cuz have not bought it in awhile,

                  yesterday im up in the springs and stop at a Shell station, regular is 209.9 cents a gallon, and premium? 274.9 cents a gallon! damn 65 cents higher that's substantial...
                  Pump had regular - mid grade and premium yet just one sticker in the middle of it and way down low so not related to any of the choices in particular that stated "contains 10% ethanol"

                  That makes regular "buy three get one free" in comparison