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Stihls view on what OCTANE to use in the 4-mix and 2-cycle engines...

Discussion in 'Lawn Mowing' started by dcplace2004, Sep 29, 2005.

  1. dcplace2004

    dcplace2004 LawnSite Senior Member
    Posts: 423

    I called Stihl and they said that minimum 89 octane but 93 would be the better choice...just like the other LCO and Stihl said, the better the grade, the less impurities, prevention of pre-detonation, less heat, less wear and tear on engine...although there is extra cost for 93 octane, the benefits outweigh the cost, and I stand corrected from past posts...
  2. John Gamba

    John Gamba LawnSite Fanatic
    from ct
    Posts: 10,812

    Thank you :waving:
  3. geogunn

    geogunn LawnSite Gold Member
    from TN
    Posts: 3,010

    I would like an explanation of the "better the grade, the less impurities".

    does a higher octane rating equal a "better grade" of gasoline?

    and how does a better grade of gasoline, which is higher octane by this definition, equal less impurities?

    is sthil saying they put dirt, crud, cr_ap or something else in the lower grades you wont get with a "higher" grade?

    their explanation doesn't sound right to me on the impurities thing.

  4. grass_cuttin_fool

    grass_cuttin_fool LawnSite Gold Member
    Posts: 3,503

    I wonder if the higher the grade the less alcohol in the gas? Seems I remember some people having issues with the oil not mixing with the winter formula of gas.I asked stihl in an email and the guy acted like it was a deep dark secret and no explanation of why 89 octane was needed other than that is what is stated in the manual
  5. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    I'm not buying most of this because it is pure bunk. The only reason to use 89 octane is for detonation. Did you know that using too high a octane rating can also be harmful? Higher octane gas is harder to burn, it resists preignition because of this. If you use too high an octane gas it can lead to carbon deposits and increased emissions because all of the fuel will not burn. High octane gas needs an appropriately high compression to burn properly, just like deisel fuel.
  6. nmurph

    nmurph LawnSite Senior Member
    from ga
    Posts: 668

    octane and impurities have nothing to do with each other. a higher octane rating does not necessarily equate to more power or a more pure fuel. octane is an additive that increases the detonation point of fuel. it does not increase the caloric value, which is where "power" comes from. that said, a higher octane of fuel can allow the spark to be advanced, or the compression rate to be raised, resulting in an increased efficiency of the burning of the fuel and a corresponding increase in power. if an engine is optimized for a certain grade of fuel, increasing the octane will not increase the power unless the engine has a management system that is designed to adjust for these new parameters. conditions such as engine load, temperature, engine condition, ambient temperature, etc. influence detonation. i don't know what specific conditions small engines are designed for, but i think you could safely assume they are built to endure some harsh conditions and i would think that small engines are optimized for those conditions, with the grade of fuel they recommend.
  7. bill w

    bill w LawnSite Member
    from Va.
    Posts: 198

    No, it is not harder to burn, it is merely more stable (like dynamite is more stable than nitro glycerine). It has a spark plug so it doesn't need higher compression to burn. Now, if the engine had higher compression, it might need higher octane.
  8. dcplace2004

    dcplace2004 LawnSite Senior Member
    Posts: 423

    but that is not in etched in stone, obviously...I would stick to 89 then...middle of the road and on the safer side...I would not go 87 though...
  9. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    Truth be known nitro is the active ingrediant in dynamite. I stand by my statements.
  10. bill w

    bill w LawnSite Member
    from Va.
    Posts: 198

    That's why I used it as an example. :D

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