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  1. #1

    top end refresh or mill head ?

    just winterized my xll1200 , wondering what to do to do to it this winter ? cylinders = 100 ,105 ,103 ,has 94hrs showing . Would top end build or ,milling head to raise the compression be more advantageous ? What is the compression psi supposed to be in stock form ? and will milling the head cause the rings to stress at this point ? the ski runs good at this point but can always be improved .

    2000 XLL , R&D intake/rideplate ,primers -chokes removed ,rejet and rebuild carbs ,Riva Fa's , D-plate ,WE clips and links ,free flow exhaust ,oil inject with oetiker clips , Skat 12/18 = 58.3 mph gps


  2. #2
    Moderator OsideBill's Avatar
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    Stock Compression runs about 115-120 PSI, your gauge may be off or the method you used may be the reason for the low numbers. Here is a great write up on pressure testing
    http://www.greenhulk.net/forums/show...mpression-Test

    A milled head will give you a great bottom end bump in performance and is a fairly safe way of increasing performance. Stay in the 145-150 PSI range to keep it pump gas friendly.

  3. #3
    actually I read that thread before I checked compression and then flushed and winterized ,would the head milling have a negative impact on my current top end ?

  4. #4
    Moderator OsideBill's Avatar
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    No it would not hurt it. Your compression is fairly even cylinder to cylinder, how well do you trust the numbers from your gauge?

  5. #5
    Yellow93's Avatar
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    Quote Originally Posted by OsideBill View Post
    No it would not hurt it. Your compression is fairly even cylinder to cylinder, how well do you trust the numbers from your gauge?
    sounds like a testing issue to me... Are you using a quality gauge such as Snap-On or a cheapo? Also, are you holding the throttle open when testing?

  6. #6
    gauge isn't the most expensive, but in this case it does show consistency in the row ,ya did all the hold throttle open and all that good stuff -the power valves were closed and selnoid disconnected . I am an amatuer but not an inexperienced engine builder and have had bad experiences with changing compression ratio with head modifications leading to blowing out the rings in an engine .

  7. #7
    Moderator OsideBill's Avatar
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    I have not seen any evidence of bumping the compression up affecting the rings on these. That of course is within reason in the 145-150 psi range, 91 octane pump gas safe.

  8. #8
    thanks for the info ,very much appreciated

  9. #9

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    Quote Originally Posted by OsideBill View Post
    I have not seen any evidence of bumping the compression up affecting the rings on these. That of course is within reason in the 145-150 psi range, 91 octane pump gas safe.

    Don't forget that if you do bump the compression with these engines that you will also have to change carburetor jetting.

  10. #10
    Moderator OsideBill's Avatar
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    Your not flowing more exhaust or intake, so I never adjust for compression. You are compressing the same amount of fuel into smaller space that's all.

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