holley street dominator vs quadrajet

Discussion in 'High Performance Modifications' started by jroach, Sep 10, 2019.

  1. jroach

    jroach Veteran Member

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    i did find the spread bore rpm on summit and saved it in my wish list. still no options for the mopar b motor only the standard performer and the offy
     
  2. biker

    biker Veteran Member

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    I totally missed that you were putting this on a mopar. The street demon is modeled after a thermoquad, so it may have a similar fuel inlet location and may be more at home on a mopar.
     
  3. jroach

    jroach Veteran Member

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    update. i was able to put my hands on a street demon carb at a local speed shop. it has the same size primaries as any square bore carb. definitely using a quadrajet.
     
  4. biker

    biker Veteran Member

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    The 750 version of the street demon has 1 11/16 primaries. The 625 version is smaller. I would have stuck with Quadrajet too if I could have got enough fuel out of the idle circuit. Great carb otherwise.
     
  5. Plant Engineer

    Plant Engineer Veteran Member

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    You guys like quadrajets a LOT more than I do but I dont deal with stock ish engines. Personally I'd look at a Pro Systems carb. Right, right out of the box most times .
     
  6. jeff swisher

    jeff swisher Veteran Member

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    Qjets will work fine on modified engines as well as stock ones. They are so tuneable it is ridiculous.
    a short read with some good part numbers for parts to modify your Qjet.
    https://www.motorstate.com/Quadrajet.htm
     
  7. cnlmustard

    cnlmustard Member

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    Swisher, 100% agree. Q-jet came in a number of variations with differant option features, pick the ones right for what your trying to do.

    Holley is a POS to tune out, have to take fuel bowls off to make any adjustment, tearing up gaskets and screws leaking every two months. And if you don't want to tune a "carbie", then just put a computerized fuel injection conversion in it and plug it in , like the other dumb bunnies who cant even fix their underwear if they put them on backwards.

    Stuff works right if right off the assembly line, but NOTHING works "right out the box". If it does, go hit the casino right now, you're on a streak!
    If you like tech, especially straight mechanical things like a grandfather clock mechanism, then the thrill is in the hunt, to adjust and modify everything to match the manifold you've chosen!
    I have the spreadbore DUAL-PORT Offenhauser. (Not dual plane) Primaries feed small single plane to bottom ports to all 8, warm high velocity for low rpm torque. The top mainifold large ports plane feed from secondaries, and stay much cooler. They're basically dormant unless secondary flows, and have 2/3 of total air flow rating. (P.S., do not put a Holley on one of these unless it's a double-pumper.) Holley vacuum secondary models have no priming flow, and the dry top plane starves bad when called for. Q'jets have big secondary surge feed wells, to handle that job already.
    When I finally gave it back for my refund, I was astounded at just how good a job the Qjet was already doing. Just needed tuning.

    Here's just one example to discover on the Q-jet that stumped me for a good while, it's not even in Doug Roe's famous book. When I opened the secondaries all the way, I would get more power by backing off a smidgeon. Why? Look at them real close, the throttle blades have to be at a sweet spot under the vertical bore baffles, or they can cause a differant balence of secondary fuel to the front cylinders vs. rear cylinders. If they're in a straight line, the main fuel feed tubes are then only feeding gas to one end's cylinders. I Dremel cut the baffles to where I could bend them a bit to have the fuel come down to evenly split across the throttle plate at WOT to make a huge difference. Cha-ching, and happy dance! That may be unique to use on this spreadbore manifold, I don't know.
    Guess what? I didn't have to spill one drop of gas to do that mod, with fire extinguisher ready.

    A q-jet has about a few hundred primary rod, primay jet, and secondary rod combinations available, and each can be adjusted to allow more or less flow by throttle position and manifold vacuum on either. Infinitely tuneble to perfection.
     
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  8. biker

    biker Veteran Member

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    Nice tip! I agree with you on the awesomeness of the qjet. However, I'm going to make the leap to FI only because of inability to tune any carb for efficient cold and hot starts because of crappy fuel and aluminum intakes. Wife and kids drive the car, so it's nice to have it start well under all conditions.
     
  9. Plant Engineer

    Plant Engineer Veteran Member

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    I feel like I've stumbled into a fat chick appreciation forum.
     
  10. biker

    biker Veteran Member

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    Once I close the hood, nobody will see the injection.
     

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