mmHg, Kg/cm2 confusion
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This is a discussion on mmHg, Kg/cm2 confusion within the Interior Mods forums, part of the Tech & Modifying & General Repairs category; I am having a bit of confusion reading my guages when i am at idle I have a GReddy boost ...

  1. #1
    Registered User Redline927's Avatar
    Join Date
    Jun 2004
    New Jersey

    mmHg, Kg/cm2 confusion

    I am having a bit of confusion reading my guages when i am at idle I have a GReddy boost guage btw. the needle sits at the bottom of the guage where it says mm of mercury, is this vaccuum? what exactly is going on with the turbo? what does this mean? what does it mean when its at 0? i feel dumb for asking, but we all learned from someone at one point.

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  3. #2
    Registered User
    Join Date
    Sep 2001
    Edmonds, Washington
    mmHg is indeed reading vacuum. When not making positive manifold pressure (like idling) or during low load cruising, the engine behaves much like a naturally aspirated engine pulling vacuum. Check out for unit conversions. You will not spool the turbo until there is a pressure difference across the turbine wheel in the hot side. Until you get above atmospheric pressure at the point you're tapping for your boost gauge signal, your gauges shouldn't go above 0, what you'll see at say .95 kg/cm^2 is boost pressure relative to atmospheric.

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