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Q for restrorob..........

Discussion in 'Mechanic and Repair' started by Gr grass n Hi tides, Aug 29, 2005.

  1. Gr grass n Hi tides

    Gr grass n Hi tides LawnSite Bronze Member
    Messages: 1,020

    I saw an off topic thread talking about gasoline octane affecting car performance. I've heard the argument about running high & low octane fuel many times, in fact my ex-father in law who is an auto mechanic swore the min. 87 rating was all anyone ever needed to run. I've also heard plenty of people swear by 93.

    But.......my question is how about these extremely hard working mower engines? I personally put only 93 in my mowers & all hand held equip. They're like race cars so I try to treat them that way even though I've been told it's a waste of money.

    What's your opinion? I've been reading loads of pages in this forum & respect everything you say. Glad you're here.
  2. MBDiagMan

    MBDiagMan LawnSite Senior Member
    Messages: 852

    There are two different answers determined by whether you have engine management with a knock sensor or not. Except for the new Electronic Fuel Injection engines, no mowers have knock sensors and the EFI engines might not even have knock sensors.

    Since your mower has no knock sensor all you need is enough octane to keep it from exhibiting spark knock. Your lawn mower engines are relatively low compression and if you are getting spark knock with 87 octane then there is something wrong with the engine. Any money spent for higher octane fuel when it is not necessary to prevent spark knock is ABSOLUTELY wasted.

    On modern cars with electronic fuel injection and knock sensors this is a different story. If your car is low compression then 87 octane is fine. If it is a high compression performance engine requiring premium, then you can safely burn 87, but when the knock is detected the computer will ****** ignition timing to prevent engine damage. The ******** timing will result in less power and poorer fuel mileage, thus making regular gas sometimes more expensive per mile than premium.

    The short answer; if you are buying high enough octane to prevent spark knock in a non computer controlled engine, then money spent for higher octane is wasted.

    Hope this helps,
    Certified Automotive Technician, ASE Master
  3. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Well Shawn, Most all small engine OEMs design and build their engines to burn the lower grade 87 octane because they know this is what the average end user is going to run. As doc said there are no knock sensors on them (yet) so in my opinion running the 93 octane is a waste of money.
    Take the extra money spent on the 93 per week and buy your lunch a couple days with it.
  4. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Messages: 2,613

    I have used regular and mid-grade in my equipment. There is a noticable difference between the two imo. The mid grade runs much better but I dont think there is any gain between mid-grade and premium.
  5. MBDiagMan

    MBDiagMan LawnSite Senior Member
    Messages: 852

    If it runs and sounds better with mid grade ignition timing may not be correct or your pistons/combustion chambers are carboned up.

    Good luck,
  6. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Ditto, Doc
  7. Gr grass n Hi tides

    Gr grass n Hi tides LawnSite Bronze Member
    Messages: 1,020

    Thanks fellas I appreciate it.
  8. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

  9. Gr grass n Hi tides

    Gr grass n Hi tides LawnSite Bronze Member
    Messages: 1,020

    lol. Yeah.......that's why I put the question to people that know more than I do. Looks like my ex father in law was also correct. Thing is he can be such an arse sometimes it's hard to swallow, lol lol. Definitely set in his ways on a lot of things, right or wrong.

    I'll be running low grade from here on out.
  10. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Sorry Jon, The way that thread was going I could tell there was NOTHING You, Me or anybody else could have said to convince Topsites he was wasting money.
    You really impressed me on how WELL you were handling the situation and had it FULLY under control, I just didn't feel the need to jump that band wagon with my 2 cents.

    Btw; laughed my a&& off with the GEICO bit ! :laugh:
    Job Well Done !!!!

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