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  1. #1
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    Member No: Mike_ZZ's Avatar

    Yes | No

    Eaton M90 Supercharger Boost Pressure

    Hi ,

    Can anyone advise if it is possible to directly measure the Boost pressure on an M90 as fitted to a GM3800 L67 V6 ? If so , where do you connect the boost gauge ??We can only ever seem to get a negative (vacuum) pressure reading , even under heavy load conditions ? Is this normal ? Any advice would be greatly appreciated.


    Mike S.
    NSW Australia

  2. #2
    John N.
    , ,
    Member No: John N.'s Avatar

    Yes | No

    Roots type superchargers (Eaton) are positive

    displacement pumps, just like 4 cycle engines. Your boost is determined by the displacement of the SC (1.5 liters/revolution for a M90). Check out this site for RPM/CFM and displacement specs.

    Then you apply the formulas from this site to get the pulley ratio (or if you have the ratio, reverse the calculation): http://mg-tabc.org/supercharger/sc-harry-pyle.htm. This calculation basically looks at 1/2 the displacement of your engine (its a 4-cylcle engine) and compares the ratio to how many liters/rpm the supercharger pumps.

    That will tell you how much manifold pressure to expect.

    (email me if you have questions)


    John N

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