Higher octaine

Discussion in 'Bubba's Outboards' started by primitivefrn, Mar 30, 2006.

  1. primitivefrn

    primitivefrn Member

    Messages:
    777
    State:
    collins mo
    does higer octain, help or hurt, say higher than 78 ? run a 175 mercury sports jet. Was woundering if higher octaine would keep it cleaner.
     
  2. TeamCatHazzard

    TeamCatHazzard New Member

    Messages:
    517
    State:
    Illinois
    Not sure in your case but sometimes too high of octane can hurt too. Someone on here will know for sure, but sometimes too much octane can hurt too.
     

  3. jim

    jim New Member

    Messages:
    2,579
    State:
    Jacksonville NC
    Do you mean higher than 87?Occasional tanks of premium will not hurt and can help because usually the premium gas has a better additive package.Most all outboard applications other than racing models call for 87 oct fuel.:)
     
  4. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    Unburned gas in a two stroke engine helps keep the cyl head temp down to the recommended operating temperature

    Now we'll go into what the additives for an octane rating does.

    It slows down the burn so you get a more complete combustion of the fuel. I'm not talking minutes here. It's mini milliseconds.

    A more complete burn results in more cyl head temp; the enemy of all two strokes.

    Everything designed into a two stroke in regards to combustion is designed to hold down and dissipate heat, From the heat transfer through the spark plug insulators to the water jacket, (Hot and cold plugs), to the recommended octane rated fuel, that keeps the cyl's from getting that glow plug effect and blowing your engine all to hell.

    For easy math, think of an engine doing 6000 rpm's. Each cyl changes direction 200 times a second. If a small particle of carbon starts to glow from too much heat or lack of being decarboned periodically, preignition occurs. That can and will blow a cyl faster than you can blink.

    At least this is how it was demonstrated and explained to me by several master marine techs. I've had no reason to doubt them.

    This post was typed under the influence of Xanax.
     
  5. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Darn good analogy bob. I knew the theory but for the life of me could not put it into words.:)
    Like I said good explanation.:thumbsup:
     
  6. Bobpaul

    Bobpaul New Member

    Messages:
    3,039
    State:
    Supply NC
    One mistake made here before I get jumped on, was that each piston in the cyl's changes direction, not the cyl's

    And let me throw this in for those that can't bring themselves to throw away old gas, a phrase called phase seporation, where the gas and oil due to moisture accumulation and age of gas, seporate and don't lubricate any longer.

    Your pistons will be fine because it'll be your bearing and one or more rods will come poking through the block.

    Ain't owning an outboard fun?:p