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Compression Test results at high elevation

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  • Compression Test results at high elevation

    Does anyone know for sure if cranking compression testing results at higher elevation are significantly changed from lower elevation?

    I've assumed it does, but have not done back to back testing. Here at over 6,000ft elevation the air pressure is roughly 20-22% less than sea level , 80kPa vs. 101kPa, or 11.6psi vs 14.7psi.

    Anyone know for sure?
    Escaped on a technicality.

  • #2
    Yes it does
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    • #3
      not as much air, won't make as much pressure when you squeeze it. Same thing here, not quite as bad (4500 ft)
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      • #4
        That's what I figured.

        I'm playing around with PipeMax and with all the settings plugged in as close to real I know them (cam timing, displacement, compression ratio, etc), it spits out a cranking compression number exactly what I measured, 135psi. Which it should be based on sea level air pressure, and straight math adding 20% the number should be around 165psi, which is what the service manual specifies, so IMO lended credence to the 135psi readings. Hmm.

        **If I plug in a compression ratio of 9.0:1 it puts it at 162psi, but all the measurements I've done don't come anywhere near 9.0:1 compression, and the measured volume for the chamber and piston valve relief's match within a cc or four of what others found on their OHC Pontiac engines.
        Last edited by TheSilverBuick; June 16, 2014, 10:29 AM.
        Escaped on a technicality.

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        • #5
          I wonder if I was a tooth off? One tooth is nine camshaft degree's, so 18* crankshaft degree's advanced is 90*, and PipeMax says 153psi then. Given how I had the adjustable cam sprocket set to something like 12*-18* advance and the engine ran okay, makes it a feasible possibility. In any case, I guess I'll be doing another compression check when it's back together.


          **Never mind, being a tooth off wouldn't account for it, as then the compression test wouldn't align itself with the service manual like it does.
          Last edited by TheSilverBuick; June 16, 2014, 10:43 AM.
          Escaped on a technicality.

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          • #6
            May I see the calibration certificate for that pressure gauge?

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