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Thread: 912 High Compression Pistons

  1. #1
    mtgsxr's Avatar
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    Talking 912 High Compression Pistons

    Ok im really wanting to do the high compression piston kit in my 912. its a early engine and just turned 30 hrs. lol yep 30. anyhow does anyone have any mid to high times on these pistons? notice any major power gains?

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    Super Moderator Av8r3400's Avatar
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    Default Re: 912 High Compression Pistons

    Define early?

    By my recent experience with my motor, an early 90's vintage 912 UL, I don't think I would consider the high compression modification without doing some other modifications, first:

    1. Over Run clutch in gearbox
    2. Updated gear set in gearbox
    3. Soft start module
    4. HD starter

    Just to start with...
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    mtgsxr's Avatar
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    Default Re: 912 High Compression Pistons

    I believe its a 1993 engine.

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    Super Moderator Av8r3400's Avatar
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    Default Re: 912 High Compression Pistons

    That's about the same vintage as mine.

    The power gains from a hc modification are real. In our engines the gear box will not like the "harshness" of the high compression power without the additional mods I listed. Figure an additional $3000 worth of parts to do them.
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    Senior Member Slyfox's Avatar
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    Default Re: 912 High Compression Pistons

    Quote Originally Posted by Av8r3400 View Post
    Define early?

    By my recent experience with my motor, an early 90's vintage 912 UL, I don't think I would consider the high compression modification without doing some other modifications, first:

    1. Over Run clutch in gearbox
    2. Updated gear set in gearbox
    3. Soft start module
    4. HD starter

    Just to start with...
    don't forget the pins for the rockers. either check them every annual or update.

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    Default Re: 912 High Compression Pistons

    I spoke with Mr. Stockton about this same issue and he reccomended going with the standard Big Bore kit. This kit gives 104 HP on the old 80 HP engines. This is a substanial increase. My engine is a 1996 vintage and am seriously considering doing this since I am not happy with the oil useage it is currently having with the 95HP ExtraPerformance kit.
    As Av8r3400 states, the additional expenses incurred with the HC nearly double the investment as a lot more needs to be changed to allow use of the HC kit.

  7. #7
    Super Moderator Av8r3400's Avatar
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    Default Re: 912 High Compression Pistons

    The big bore kit is more money than the hc pistons, but I would agree, in the long run, the big bore would be much less stressful to the rest of the engine and it's systems, requiring fewer additional repairs or modifications. This would make it overall a less costly way to get more power from a 912UL.

    As an aside, in about 1995 the gearbox components were updated. The gears were widened and the oiling inside the gearbox flowed differently. This makes the later model gearboxes more robust, in my opinion.
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    Default Re: 912 High Compression Pistons

    Ok, my apologies. I have been following the thread on the Big Bore kit and mistakenly assumed this was what was being asked. I see the error of my thinking. The question was refering to just high compression piston kit.

    Needing to back track a bit and say that you need to disregard my comments on my previous post.

    I will comment on the little I do know about the high compression pistons of standard bore. I bought a plane with these pistons already installed so can not really give an opinion of them over the stock pistons. My plane definitely is not lacking for power and I would be 100% satisfied with it other than its slight oil usage. I have had a difficult time in finding anyone with a lot of time on this conversion but the couple of I have spoken with say this is normal. I think the way it was explained to me was the metal used in these pistons causes a difference in the expanding and conracting of the cylinders/pistons. Supposedly the oil useage I am experiencing is totally acceptible. I am not happy with it and have been looking to either rering the engine or get the big bore kit.
    Not a Kitfox, but there is a gentleman in Canada that deals a lot with RANS S-7's and he had stated that there was a considerable performance gain with the high compression piston kit when they were installed in an S-7 that was on floats. He has a couple of sites with a lot of good information on Rotax mods such has thermostats, heaters, etc.

    If you want to broswe them:

    www.stoneylake.org/pipcom/rans.htm
    www.ranss7.com/

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    mtgsxr's Avatar
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    Smile Re: 912 High Compression Pistons

    Thanks for the input guys

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    Default Re: 912 High Compression Pistons

    I recently installed the high compression pistions in my older 912 with no heavy duty starter no slipper clutch, no soft start. Runs good, nice power increase. the pistions are a work of art when you get them, there so pretty you want to put them in. the extra oil passage for the wrist pin is a nice up grade. I would recemend them.

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