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  1. #1

    Do these compression #'s look ok?

    Just rebuilt my motor. Have not broken it in yet. Started and ran for a total of around 2 minutes to check oil pressure, fill coolant, etc. On a cold motor the compression is running 165#. The cam (Rotax B kit cam) is advanced 3 degrees and the head is shaved .030. Last year, before the rebuild, I was running around 130#. Don't know where the cam was set exactly. It was either straight up or slightly retarded as near as I could tell.

    Does this sound ok?

    Thanks

    Mark


  2. #2
    speedskixp's Avatar
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    Mark, that seems pretty high, especialy if you plan on running big boost. You should warm the motor up good before testing next time to get a more accurate reading and then adjust your cam to get the compression down between 130 and 140 if possible,

  3. #3
    If my compression really is 165#, does that mean I may detonate earlier? Or is this just static compression that has more to do with cam timing? I'll check compression again on a warm motor and see what it is. I wouldn't think advancing the cam 3 degrees would make that much of a difference in compression readings. I was only showing 12# of boost last year on a Rude1 charger. Cam timing may have had something to do with that.

    Thanks

    Mark

  4. #4
    speedskixp's Avatar
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    Quote Originally Posted by Mark S View Post
    If my compression really is 165#, does that mean I may detonate earlier? Or is this just static compression that has more to do with cam timing? I'll check compression again on a warm motor and see what it is. I wouldn't think advancing the cam 3 degrees would make that much of a difference in compression readings. I was only showing 12# of boost last year on a Rude1 charger. Cam timing may have had something to do with that.

    Thanks

    Mark
    The cam timing wont effect your static compression but it will effect your dynamic compression and can and will cause detonation. You should play with your cam timing some and see what happens. Make sure you get it warmed up first also.

  5. #5
    2006 Turbo RXP boBO's Avatar
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    On ROTAX B kit your compression MUST be on 135PSI

  6. #6
    Live to RIDE. brendus's Avatar
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    for those uneducated like me could you guys please explain on how to change the timing of the cam. if running higher boost then pressure should be less? cheers

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    2006 Turbo RXP boBO's Avatar
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    Very easy PM sent

  8. #8
    What would be the effects of running higher than 135# compression or running lower than 135# of compression? I assume if you advance the cam you run higher compression and if you retard the cam you run lower compression?

    Thanks

    Mark

  9. #9
    West Texas RXP skoepp's Avatar
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    Quote Originally Posted by Mark S View Post
    What would be the effects of running higher than 135# compression or running lower than 135# of compression? I assume if you advance the cam you run higher compression and if you retard the cam you run lower compression?

    Thanks

    Mark
    Mark, when i retarded my 04 cam i saw a slight decrease in compression. Right now with my cam retarded I am seeing 135 to 140 # compression.

  10. #10
    speedskixp's Avatar
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    Quote Originally Posted by Mark S View Post
    What would be the effects of running higher than 135# compression or running lower than 135# of compression? I assume if you advance the cam you run higher compression and if you retard the cam you run lower compression?

    Thanks

    Mark
    Yes.
    Advancing the cam will ussualy give you better bottom end but you have to worry more about deto. Retarding the cam should result in a gain in rpms.

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