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Thread: SHO Compression

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    mjh3ides's Avatar
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    SHO Compression

    Has anyone done a compression test on their SHO/FZ? I had an overheat over the weekend & when I checked it I'm seeing 140, 135, 135, 130 psi in the water @ full throttle. I checked the svc manual & I saw the comp. should be 87psi.


  2. #2
    SHOBiz's Avatar
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    My research has shown 140-150PSI is perfect.

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    speedskixp's Avatar
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    Quote Originally Posted by mjh3ides View Post
    Has anyone done a compression test on their SHO/FZ? I had an overheat over the weekend & when I checked it I'm seeing 140, 135, 135, 130 psi in the water @ full throttle. I checked the svc manual & I saw the comp. should be 87psi.
    Your compression sounds good to me . All of your cylinders are within 10% so I would not be concerned. It sounds like your service manual is wrong.

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    how did you check compression on the water at full throttle????

    I thought the only way to do it was have the ski up on the trailer with all the spark plugs out??

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    Quote Originally Posted by smbstyle View Post
    how did you check compression on the water at full throttle????

    I thought the only way to do it was have the ski up on the trailer with all the spark plugs out??
    +1

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    smbstyle's Avatar
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    Quote Originally Posted by gmoeller View Post
    +1
    I used a crappy pressure tester from autozone, and didn't get it tight enough in there probably, but I was seeing about 110-115 after a few cranks...

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    mjh3ides's Avatar
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    Quote Originally Posted by smbstyle View Post
    how did you check compression on the water at full throttle????

    I thought the only way to do it was have the ski up on the trailer with all the spark plugs out??
    I just backed the trailer into the water & did the check at the ramp...after letting it warm up for a few minutes. I got the same #'s I saw when I tested it at my house when it wasn't under load.

    I just looked at the svc manual & it says to remove all the plugs before testing. I've always heard you should remove one plug at a time. Not sure what the proper method is??? There was also no mention in the manual of holding the throttle open, which is how I checked mine. Is this why I was seeing a much higher compression reading than the 87psi spec from the manual?

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    RUSH.'s Avatar
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    Quote Originally Posted by mjh3ides View Post
    I just backed the trailer into the water & did the check at the ramp...after letting it warm up for a few minutes. I got the same #'s I saw when I tested it at my house when it wasn't under load.

    I just looked at the svc manual & it says to remove all the plugs before testing. I've always heard you should remove one plug at a time. Not sure what the proper method is??? There was also no mention in the manual of holding the throttle open, which is how I checked mine. Is this why I was seeing a much higher compression reading than the 87psi spec from the manual?

    you need to check compression with all the plugs out and the gauge in one at a time. Hold the throttle wide open and turn over engine with the starter, not running.

  9. #9
    smbstyle's Avatar
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    so hold the throttle open when cranking with all plugs out is the proper way?

  10. #10
    This might sound really dumb and be way off.... But wouldn't your compression reading change depending on what supercharger wheel you are running?

    I'm not sure about the first part, but I do know that you should pull all the plugs, hold the throttle wide open and turn the motor over using the starter to check the compression of each cylinder one at a time.

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