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Thread: Q-Jet question

  1. #1
    DJW
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    Q-Jet question

    Can anyone tell me what CFM the Quadra-jet carb is on a stock Merc. 7.4L. (330) If I change intakes to a Edelbrock performer RPM, should I buy their marine carb or will the Q-jet be good enough? Thanks

  2. #2
    Official OSO boat whore Charter Member
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    I think it's 750 cfm. For a stock motor, I'd stick with the quad.

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    Stick with the Q Jet merc uses them to 400hp should be a 750 parts are easy to get easy to tune it is a better carb than the edelbrock the small primary helps also.

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    DJW
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    Thanks for the info, could you guys make a suggestion on what intake to buy for the 330. I understand that the stock intake is not of very good quality performance wise. Note that I have upgraded the exhaust already. I am hopeing to gain 4-500 rpm's with the exhaust and intake combination upgrades. I have seen good results from someone using the performer rpm duel plane but is there something better. How about the performer air gap?

    Thanks

  5. #5
    Scott72
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    If you are running in salt water and don't have closed cooling it's hard to beat the stock Mercruiser Highrise that came on the carburated magnums. The one I had was aluminum but had brass inserts to resist corrosion.

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    Square peg and round hole?

    I think you would have an issue with the intake ports not matching up if you use a stock magnum intake. Magnums have the larger rectangular port heads, whereas the 7.4's have the small round ports. Not saying the engine wouldn't run, but you probably wouldn't see any gain and you might hurt your performance. But you could go ahead and switch to the square port magnum heads while you are at it, and see some real gains!

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    Thumbs up

    Edelbrock Performer RPM or RPM air Gap. Quite a few car magazines have written this one up as making as much power on the low end as the regular Performer, with more up top. I've got one on my 330, works great. Clearance was fine also...

  8. #8
    Scott72
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    Must be a morning thing. Didn't even think about oval ports on the 330 hp. If you do run in salt water, just remember all the manifolds mentioned are aluminum. I run an aluminum manifold in salt water and only hope to get 2-3 years out of it.

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    Scott-I believe that the corrosion would start around the thermostat. Perhaps you could try a stainless one instead of the brass one. I'm not sure, but I believe the stanless is closer to aluminum in terms of dissimular metals. If nothing else, put some never-seize or a o-ring below it to keep the metals apart.

  10. #10
    Scott72
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    Thanks for the advice, Cord. I have installed a flush kit on the new motor. Hopefully that will help. Salt water is amazing compared to fresh. My old boat was a fresh water boat for 10 years. Pulled a riser and they looked brand new. Three years in salt water (without flushing the motor) and the risers basically crumbled in my hands. I had to replace the thermostat housing due to corrosion and the intake manifold was almost due.


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