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Thread: Harley & petrol octane

  1. #1
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    12th April 2006 - 18:44
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    Harley & petrol octane

    What petrol do you use for your Evo engines in NZ - 91 or 98 octane? My engine temp is 175-210, depending on the weather. In Asia where I lived before coming here, we only had one choice. I'm running mine on 91 at the moment but it is running a little erratic, which could be the jetting being so close to sea level - plugs look fine though. I don't think it's pinging but I might try 98 next time.

  2. #2
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    20th October 2005 - 22:25
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    Quote Originally Posted by rok-the-boat View Post
    What petrol do you use for your Evo engines in NZ - 91 or 98 octane?
    I use only 96 and the engine runs smooth as.

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    98' FXDWG
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    Hope this helps.
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  3. #3
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    We use 95 on our rental bikes.
    Speed doesn't kill people.
    Stupidity kills people.

  4. #4
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    OK, I'll try a higher octane next time I fill up. Thanks for the input.

  5. #5
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    I use 91 in the lawn-mower, you trying to say it can be used on other motors??
    Winding up drongos, foil hat wearers and over sensitive KBers for over 14,000 posts...........
    " Life is not a rehearsal, it's as happy or miserable as you want to make it"

  6. #6
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    Quote Originally Posted by scumdog View Post
    I use 91 in the lawn-mower, you trying to say it can be used on other motors??
    Try it in the Dyna-plow, you'll get through the back 40 much quicker.
    Speed doesn't kill people.
    Stupidity kills people.

  7. #7
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    we use 91 on our rentals.never had a problem
    "more than two strokes is masturbation"
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  8. #8
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    You want to use anything more than 88 octane in a Hardley? Don't they run at like 6:1 compression ratios?

  9. #9
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    91 is perfectly fine for Evos although it can make them protest a bit if you load them up in too high a gear. Blame the petrol if you like although that may not be the whole truth.

    I use 95 or higher in mine. Just because.

  10. #10
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    i have only ever used 91 - havent had any reason to use 96

  11. #11
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    Quote Originally Posted by xerxesdaphat View Post
    You want to use anything more than 88 octane in a Hardley? Don't they run at like 6:1 compression ratios?
    No they don't.

  12. #12
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    Quote Originally Posted by xerxesdaphat View Post
    You want to use anything more than 88 octane in a Hardley? Don't they run at like 6:1 compression ratios?
    Only ones running cracked CBR heads on them.....
    Winding up drongos, foil hat wearers and over sensitive KBers for over 14,000 posts...........
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  13. #13
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    I think mine ran on bourbon.

    It was always wobbling and coughing.
    David must play fair with the other kids, even the idiots.

  14. #14
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    Quote Originally Posted by scumdog View Post
    Only ones running cracked CBR heads on them.....
    Lol!! Green rep awarded

  15. #15
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    But seriously though, notwithstanding poor Honda cylinder heads with cracks , as near as I can work out the Evo engine has about an 8.8-8.9:1 compression ratio. Now, according to everything I've read, octane rating is purely a rating to ascertain the anti-compression-ignition properties of a given fuel. Now, I understand that some cylinder head designs are more susceptible to compression-ignition (or detonation) than others -- I just recently read some stuff about cages with Ricardo heads, with `squish points' and stuff like that, designed to avoid detonation -- but the biggest factor in detonation is the amount of compression the charge is under.

    So if a CB250RR with an 11.5:1 compression ratio can run 91, why can't an Evo with an 8.9:1 compression ratio?

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