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  1. #1

    50.2 hour compression check

    Decided to do a compression check before I put the GPR into hibernation.
    cold motor, WOT;
    Front cylinder: 1st crank: 132 second crank 130
    Middle cylinder: 132 132
    Rear cylinder: 130 132


  2. #2
    Altezza01's Avatar
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    what head do you have?

  3. #3
    Quote Originally Posted by Altezza01 View Post
    what head do you have?
    stock, the ski is all stock...

  4. #4
    Mike's GPR's Avatar
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    Thats exactly how mine reads with a stock head. Looks like your in good shape

  5. #5
    mtrager's Avatar
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    Pr,

    Make it 160 lbs.

  6. #6
    African-American
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    i thought 150psi was the max on a stock motor.

  7. #7
    I thought 150 is just a suggestion unless this motor is a special yamaha motor, I am running my bb 760 up to 190 on pump gas, my 550 runs 180 on premium and good oil. Had a my builder say 190 with several backup opinions on it say its ok on high octane and good oil as long as I dont go crazy on the timing and the exhaust is opened up a bit. The faint of heart may disagree but I trust these guys, with my money and my motor

  8. #8
    cheatin' piston popper addicted's Avatar
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    yours are 2 cylinders. 150 is stock on a 2 cyl. 150 is considered the limit for pump gas on a triple.

  9. #9
    DAGO RACING CREW 97GPSLEEPER's Avatar
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    I will also add GPR guys with powervalve motors get away with more compression than non-powervalve motors because at WOT the valves open and the compression drops around 10psi.

    Now, someone please explain to me why the "safe" compression on 2 cylinder is higher than that of a 3 cylinder. I have always heard this but have never been able to understand it on my own.

  10. #10

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    Quote Originally Posted by 97GPSLEEPER View Post
    I will also add GPR guys with powervalve motors get away with more compression than non-powervalve motors because at WOT the valves open and the compression drops around 10psi.

    Now, someone please explain to me why the "safe" compression on 2 cylinder is higher than that of a 3 cylinder. I have always heard this but have never been able to understand it on my own.

    HEAT to DETONATION to DESTRUCTION!! Thats why 800 PV motors are ported more aggressively than 1200/1300, because twins handle the extra load heat better than triples.

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