Gas-Vs-octane-Vs- unleaded

Discussion in 'Bubba's Outboards' started by corklabus, Mar 25, 2008.

  1. corklabus

    corklabus New Member

    Messages:
    359
    State:
    West Virginia
    owning an older 2 stroke Evinrude (1974), I'm wondering : We now have unleaded fuel with regular at 87 octane.
    Knowing that older auto engines required leaded fuel and those octane ratings were higher, I'm wondering if I would be better off all around to use 93 octane for my fuel mixture and if it would be necessary to include a lead additive ?
     
  2. jim

    jim New Member

    Messages:
    2,579
    State:
    Jacksonville NC
    I wouldnt worry about going to the higher octane but adding the lead additive wont hurt.
     

  3. rich-online

    rich-online New Member

    Messages:
    343
    State:
    California
    Speaking in general, the octane rating determines how much the air-fuel mixture can be compressed before it explodes on its own. The higher the octane, the greater the compression. That having been said, an engine designed for a lower octane fuel can safely burn a higher octane fuel, and using a higher octane fuel than required is a waste of money.

    On the other hand, using a lower octane fuel in an engine designed for a higher octane fuel will ruin the engine. If I'm not mistaken, "knocking" is one of the symptoms/sounds in this situation.

    At any rate, I hope someone out there has a manual for your engine. Good luck!

    -- Rich
     
  4. Wabash River Bear

    Wabash River Bear New Member

    Messages:
    3,019
    State:
    Indiana
    Just run plain ol 89 octain unleaded without any other additives other than your premix oil and Seafoam. The big leaded or unleaded issue with automotive engines is the valve seats. The older leaded required engines had softer valve seats and the added lead kept em from warping and/or coming out of the head. The newer engines have hardened valve seats and dont require lead additives to the fuel. Your 2 stroke dont have conventional valves, no lead needed.
     
  5. BailBonds

    BailBonds New Member

    Messages:
    282
    State:
    Indiana
    This subject usually starts heated discussions among those that really don't know what octane is. It is a measurement of the fuels ability to prevent detonation. Period. Higher octane does not burn hotter, does not produce more horsepower. Not that many years ago (maybe still) they used little 4-stroke engines to test gasoline as samples were taken from the "cracker" at the refinery. Alcohol has a higher octane rating that's why they use it in some race cars. They have high compression pistons. The higher the compression the higher the octane fuel you must use. Thus the myth that high performance engines use high octane fuel so high octane must mean more power. Using any higher octane than is required for a given compression ratio is a waste of money.
     
  6. BKS72

    BKS72 New Member

    Messages:
    3,361
    State:
    East of KC
    Thank you guys! I never knew that! I used to work at a very small airport in central IL and when I wasn't cooking in the restaurant I'd fuel planes. Every now and then I'd get some guy willing to pay $1.75 a gallon (expensive back in '88 or so) for avgas for his stock camaro or firebird. Too funny!
     
  7. corklabus

    corklabus New Member

    Messages:
    359
    State:
    West Virginia

    Thanks guys.

    Being an old mechanic, I knew most of this stuff, but sometimes the old brain needs a little kick in the pants to make the old info pop back in to place.
    Since I'm new to boats and two strokes, I wasn't sure what the valve situation was.
     
  8. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Cecil 2 strokes don't have valves per say as you and I know them in the heads. The do have a system call reed valves that are pre set at an exact opening to intake certain amount of fuel and when one of them breaks or goes to acting wrong it can wreak havoc on a motors action. The most common Thing I have seen is that when one breaks it will cause fuel to spit back out through the mouth of the carb. Not a whole lot unlike a V8 carn engine after it has droped a lifter.
    In your older engines the 87 octane will do fine and any higher then regular of today is a waste of money. It will cause one to over heat at times.
     
  9. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    --------------------------------------------------------------------------------

    This subject usually starts heated discussions among those that really don't know what octane is. It is a measurement of the fuels ability to prevent detonation. Period. Higher octane does not burn hotter.

    The higher the octane rating, the slower the gas burns, giving it a more complete burn in the cylinder. This allows the engine to produce the maximum hp that it was designed for.

    2 strokes don't like that complete burn.
     
  10. Dave53

    Dave53 New Member

    Messages:
    411
    State:
    Lonedell M
    When I bought my new 4 stroke 25 horse Mercury two years ago and it ran great on regular octane gas. I put premium in it and it seem to run even better. Now you are saying that it is all in my head? It seems faster out of the hole and top end seems to me to be faster? So the higher octane gas has nothing to do with this?
     
  11. 1sporticus

    1sporticus Active Member

    Messages:
    1,006
    State:
    Iowa
    Years ago they required the use of white gas in 2 cycle engines. Which is precisely what 87 octane is. Later Andy
     
  12. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill

    Dave I do think we were talking about 2 strokes and yours being a 4 stroke I couldn't begin to tell you what To burn in it. Thats like comparing apples to oranges.