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should i use higher octane fuel for blower/trimmer?

Discussion in 'Mechanic and Repair' started by slicey, Jun 17, 2005.

  1. slicey

    slicey LawnSite Member
    Messages: 28

    OK, i'm the proud owner of my very 1st blower and trimmer-stihl's bg85c and fs80r. what i'm curiuos to learn is; is there an emperical performance increase when using a higher octane fuel, like 92 octane for example? or should i just save the extra money towards my 2-cycle oil? thanks!
  2. Lawn Masters

    Lawn Masters LawnSite Senior Member
    Messages: 850

    I dont notice any real difference in performance, but these arent really high compression engines either, unlike a Stihl 066, which is something you'd run nothing but premium in.
  3. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    Well perhaps it doesn't get you extra rpm's but I used to run cheap AND even name-brand 87 octane and what I noticed more than anything, I went through a pull-cord about once/month between all my machines. I must've replaced a dozen pieces of string that year, thou yes I could brag they all started in 1 pull...

    Then I switched to Amoco Premium and now:
    - Not only do they start in 1 pull but they start a LOT easier. I replace maybe 1 starter cord (maybe 2) the entire year AND I never get that sharp pain in the neck from over-exerting myself while pulling on the WB's 15hp Kohler. Matter of fact, I can pull-start the Kohler with my left hand like a princely phaggot and it starts.
    - On the mix, I notice I almost never have to use the choke on the backpacks AND my sparkplugs last longer (as do fuel filters on the WB's).
    - It smells much, much better all the way around.

    There is one other thing:
    Octane is to fuel like what carbonation is to soda. If your fuel is in a can and the can gets HOT (like from the sun), when you open it, air pressure escapes with a hiss - That's your octane blowing away. Yes, you can watch fuel develop bubbles when it's in the heat, and I swear it acts like soda, and as those bubbles develop, your fuel loses octane.
    So the longer fuel sits around, the more octane it loses, just like soda loses carbonation, fuel will eventually go flat (and it smells bad) thou it does take a long time, still, the loss of even a few percents of octane has me convinced: Amoco 93-octane for everything.

    There is actually a TON more, I could tell you about the issues of dirt in fuel affected by the tanker truck re-filling your service station's underground tanks in ADDITION to how much the fuel MOVES (i.e.: If a type of fuel is purchased a LOT, then it MOVES a LOT). A fuel has to move some but not too much in order to retain cleanliness - If it moves too little, it goes bad over time... If it moves too much, sediment and debris gets stirred up in it but more so because the truck has to re-fill the tank fairly every day.
    Yes, underground service station fuel tanks hold about 10 thousand gallons of gas and a busy station fuels out about 3-5 thousand gallons (or more) per day while a tanker truck holds around 9 thousand gallons (I can't remember if it's 8700 or 9200, but it's in that range).

    The small difference in price between cheap 87 and nice 93 octane is recovered many times over by easier starts, dependable runs, and critical fuel-dependent parts longevity.
  4. grass_cuttin_fool

    grass_cuttin_fool LawnSite Gold Member
    Messages: 3,526

    It has something to do with the amount of alcohol blended in the gas. If it has a certain % of alcohol then the oil doesnt mix very well with it. The higher octanes have less alcohol and less chance of the oil seperating from the gas. I think this is correct, I have never used anything but 87 octane but the next can I mix will be atleast 89 octane from now on, Its not worth taking a chance on messing up my trimmers and blowers
  5. mcdansley

    mcdansley LawnSite Member
    Messages: 14

    What about your thoughts on using a higher octane fuel in 4-cycle engines (mowers)? I have a 6 hp Kawasaki, and currently use 87 octane with Sta-Bil added to it. Is there any advantage to using a higher octane fuel?
  6. KLLawn

    KLLawn LawnSite Member
    Messages: 13

    I try to use at least 92 octane on my Echo bp blowers and all my lawnmowers. A few years ago on lawnsite , viewers discussed this very issue and all said that Echo OPE benefits from higher octane. I started using 92+ and it was a big difference. I think Echo manuals state the use of a higher octane fuel.
  7. HK45Mark23

    HK45Mark23 LawnSite Member
    Messages: 200

    Gas is an explosive. This means that it burns faster than the speed of sound.

    Octane retards the explosive properties of gas. In doing so it transforms gas into a propellant witch burns slower than the speed of sound.

    In this state the burn time of gas is greatly reduced proportionately to the percentage of octane fortification.

    The significance to this information is; if gas was at time of detonation to explode then the release of energy in the form of expanding gasses would be extremely rapid and the yield would be low. But if you ****** the burn time and hence the expansion and release of the gasses then youÂ’re able to extract more energy from the fuel and over a greater period of time.

    Look at it like this. If you were to use gas with no octane, the explosion would be over before the piston could have moved even a quarter of an inch. Faster than the speed of sound the gas would have burned and the expansion and released of the gasses would be over. The yield of gases would also be less.

    On the other hand the higher the octane the slower the burn hence a longer burn time and also pressure from expanding gasses for a longer duration during the power stroke.

    In all the manuals I have it says to use the lower grade fuel. But it would stand to reason that any internal combustion engine would benefit form higher octane. Higher octane is more efficient and easier on the components of the engine.
  8. Oldtimer

    Oldtimer LawnSite Bronze Member
    Messages: 1,459

    I have used Amoco and only Amoco as a shop fuel for 20 years and recommend it above all others. I use 89 octane with 50:1 Shindaiwa mix oil in everything. There is no straight gasoline allowed in my shop and there are no fueling mistakes possible. The oil goes in the drums before they are hauled to the gas station.

    It seems that the smaller the engine the more sensitive it is to fuel. This is usually the result of discount station, big box store fuel or old fuel that the customer has stored for a few months. When fuel goes thru several heating and cooling cycles, especially in small vented containers, it loses it's light ends and small engines become very difficult to start.

    My estimate is that 90% of the 2 stroke engine problems we see are fuel related. The customer says "my car runs just fine on the 87 octane from the big box store so my weed eater should too". Yesterday a customer brought in a small Stihl line trimmer and felt he had a warranty repair because it was hard to start and wouldn't idle. We changed out the fuel and it was perfect.

  9. bill w

    bill w LawnSite Member
    from Va.
    Messages: 198

    My understanding of octane is that it is a measurement of resistance to pre-ignition and detonation. Most 2-strokes that I am famiiar with call for 89 octane fuel...mid-grade. Any higher octane rating is a waste of money. Any lower octane rating is a risk of a burned piston.
  10. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    *ALL* my base runs 93-octane: Truck, wb's, everything... but it's all carbed.
    Course on EFIs you need to read your manual and use whatever it calls for - carbureted: run 93, EFI: run what the manual says.

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