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Thread: 912 High Compression Pistons

  1. #11

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    Default Re: 912 High Compression Pistons

    Can anyone clarify whether you need to up-rate your spark plugs with the high compression conversion? The UL is listed using 7E plugs and the ULS 8E.

    A tad confused as my 912 has light blue CH covers, not black and not green.

    They were apparently supplied with the high Compression conversion done by the previous owner. I can't seem to locate any literature on the kit or the procedures.

    Any light to shed?
    Many thanks all
    Zeke

  2. #12
    Super Moderator Av8r3400's Avatar
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    Default Re: 912 High Compression Pistons

    Yes, you want to run the 8E plugs, same as the 912 ULS.

    The blue rocker box covers must have been painted by the previous owner. I had mine powder coated yellow just to be different.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
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  3. #13

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    Default Re: 912 High Compression Pistons

    Thanks Av8r4300, fast response!

    The Rocker covers came that colour with the kit I am told. I've seen a similar shade on some internet searches for this engine type - perhaps it is a French thang?

    Can you (anyone) point me at any official documentation for the upgrade that confirms this as my local AMO mechanic is sceptical. I found something called a 912xtra conversion kit - not sure this is the one. It also stipulates 8E (with a 0.22 mm gap!?!), and higher octane fuel, for the 95hp conversion. So I'm leaning toward that as the solution.

    Thanks again

  4. #14
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    Default Re: 912 High Compression Pistons

    Zeke,
    Are you referring to the Zipper kit or the Extra-Performance piston upgrade?
    I originally had the Extra-Performance (High compression) pistons in my my plane. They were already installed in the engine when I purchased it. The instructions did include a change of spark plugs and also required higher octane fuel.
    My Zipper High Torque kit, used the same upgraded plugs as used in the Extra kit.
    I can't give you any help on the Zipper high compression kit since it is bigger cylinders and higher compression pistons. I just looked at the Zipper webpage quickly, but didn't see any mention of plugs, but I am thinking that there is a change.

    Ok, I guess Av8R3400 responded as I was typing.

  5. #15

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    Default Re: 912 High Compression Pistons

    Appreciate Much!
    It's a tricky one to get a definitive answer on but this is the third push in the 8E direction I've had - Actually the 4th. The engine has very infrequently given me a feeling that it's not firing right - like a change in pitch on the cruise, not a miss but sort of like that. A drop in power, briefly and then all OK again. It's happened twice in the 80 of hours I've put on her to date. She must have been telling me something! Apparently incorrect plugs can do that. Never had it happen to me before tho.

  6. #16
    Super Moderator Av8r3400's Avatar
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    Default Re: 912 High Compression Pistons

    I can not give you any "official" documentation, only anecdotal information I got from Hal Stockman, the designer of my big bore kit. His advise to me was that any modification beyond the UL specs, in displacement or compression, he recommends the "8" spark plugs. Additionally, on Hal's advise, I run mine at .020 - .022" gap. These are not very powerful ignitions to handle a wider gap.

    Mine is the "low" compression kit, so 87 octane is fine. Again he instructed me that any compression above mine requires at least 91 octane.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  7. #17

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    Default Re: 912 High Compression Pistons

    Well that wraps it, Thanks Av8r3400 and WWHunter - you guys have been a great resource ahead of the weekend!

    I'll run the 8E's for a bit and see how we go. I can get 95 Octane so will stick to that too.

    Very interesting to learn about the Zip Kit.
    All the Best
    Safe Flying
    Zeke

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