[Question] 1992 454 Mercruser Magnum / Holley Conversion
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1992 454 Mercruser Magnum / Holley Conversion

  1. #1
    Member $BLOWNNYS's Avatar
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    Default 1992 454 Mercruser Magnum / Holley Conversion

    Anyone out there have any experience in knowing if a Holly squarebore or spreadbore will fit the 1992 454 Magnum Mercruser Stock Aluminum Manifold. Tired of the stock carberator and its hard starting, ( lot of cranking ).

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    Senior Member Hullshot's Avatar
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    Quote Originally Posted by $BLOWNNYS View Post
    Anyone out there have any experience in knowing if a Holly squarebore or spreadbore will fit the 1992 454 Magnum Mercruser Stock Aluminum Manifold. Tired of the stock carberator and its hard starting, ( lot of cranking ).
    Yes it will

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    Senior Member f_inscreenname's Avatar
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    I think you will have to use a spread bore or one of those aluminum adaptors. Lots of cranking with a carb that has sat around dry for a long time sounds like the accelerator pump may have dried up.
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    Member $BLOWNNYS's Avatar
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    Thanks everyone.

    I have a 750 Holley w/ vacuum 2nds, it is not a marine carb. If I must purchase a new carb, I was thinking of a mechanical 2nds 800 to 850 double pumper.

    Any thoughts.

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    Default Carb suggestions

    If its just the stock 454 there rated from 290-330hp. The quad carb on there has a pretty small bores as are the oval port heads. Putting a larger carb will kill the velocity, hence hurting low end performance and torque. You could get away with running a 650 CFM Holley. Marine carbs have the safety overflow turn downs for the float bowls to keep from pouring gas all over the intake if the floats ever stick. Also, you have the fuel pump inlet incase the fuel pump diaphragm leaks. the yellow hose that runs from the fuel pump to the side of the carb. If you get some decent heads and compression over the stock 9-1. Then i would get a bigger carb. Otherwise your just going to run very rich. The Holley adapters are easy to find. But then your going to need a new throttle cable bracket cause your existing one will not fit with the Holley. Mike

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    mjc
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    I put a 800 dp on my 454 mag and it ran real good started easy even with the choke cut off

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    mjc,

    Any issues with the install, special part needed??

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    Yes there is a universal adapter plate. Switched to Carter AFB with much improved starting.

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