Just purchased a '67 Coronet 440, and it's slow...

Fuel and Air Systems

  1. chillbill

    chillbill Active Member

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    I just purchased my first classic Mopar, a 1967 Coronet 440 with 87k miles, a stock 383, 4bbl carb, 3 speed 727 torqueflite, and a 8 3/4 rear end.

    This was originally a 2bbl so I believe it was originally rated at 280hp. However, right now it feels more like 150hp. The first gear acceleration is "fine", but it feels the car starts to become sluggish after 30mph and acceleration decreases. I'm not expecting it to perform like a modern car but I think this motor can do better.

    Last night I checked the numbers and the intake is a Chrysler unit from a 440, with number 3830949.
    Edit: People have suggested below this is from a 400, not a 440.
    The carb is a Rochester Quadrajet 17086046. This is a GM carb that came on 4.3l trucks. https://www.carburetion.com/CarbNumber.asp?Number=17086046

    I'm not an expert here but I think this intake and carb combo is not the most efficient. Are there any power/torque gains to be had with a different carb? I know it's a stock, tired engine with a 3 speed but I'm sure it can do better.

    Any suggestions?
     
    Last edited: Jun 25, 2021
  2. chillbill

    chillbill Active Member

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    Here's a pic of the carb. It's got a leak and that's probably not helping...
    upload_2021-6-23_15-26-21.png
     
  3. Michael_

    Michael_ FBBO Gold Member FBBO Gold Member

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    I'm pretty sure it will do better with a stock intake and carburetor as long as the engine is in good shape and everything else is stock.

    I'm not really surprised the engine runs like crap with that MacGyver combo.

    Recently found out our 72 cutlass supreme has a late 70s emissions quadrajet on it.
    While running pretty good (intake and everything is correct, though) i ordered the right one and hope to gain a few hp ^^
    (But the main reason is i want to install a factory cruise control kit and it would not work with the late 70s carb.)
     
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    • diesel_lv

      diesel_lv Well-Known Member

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      Not sure how someone fit a 440 intake manifold on a 383. My '67 440 4dr was a bone stock 383 2bbl 727 that I inherited from my Great grandmother. 78k on it when I got it in '96. It would light the tires and beat stock 5.0's light to light.
      Definitely some issues to resolve there.
       
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      • Cojohnso1

        Cojohnso1 Well-Known Member

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        This certainly sounds like too much carb and intake for the build. It wouldn't surprise me if you evaluate the plugs? It will look and very possibly running lean. Especially if vacuum secondaries? So what to do? I would go back to a 2 barrel setup. There are performance options even with 2 barrel. Or? A build of 383 with heavier cam and head work to accommodate a higher HP build. If running lean? This can cause cylinder wall and piston damage over time. Too big a carb is a classic mistake done by many. Bigger isn't always better. This of course is just recommendation from the cheapseats. Only based on your observations.
         
      • chillbill

        chillbill Active Member

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        Hmm so it's possible it's not a 383? It doesn't have the engine number on the front left so I'm assuming it's near the distributor, making it a B engine.
         
      • chillbill

        chillbill Active Member

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        Here's a pic of the intake numbers
        qYzF6VH5fWJpumhNu2OF1NqOlwtZEQqP0rdERDq1JR4GO5KLXtfFCTyGDcR1I5nOY9xSdA=w1422-h1896-no?authuser=1.jpg
         
      • chillbill

        chillbill Active Member

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        I'll definitely check out the plugs. Also planning on doing a compression check. I'm not planning on a major build yet so will stick to intake and carb for now.
         
      • Michael_

        Michael_ FBBO Gold Member FBBO Gold Member

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        I think you should identify the engine first before doing anything else.

        I dont know anything about his carb and i'm not an expert by any means but if it's coming off a 4.3l truck engine, how can it be to large?
         
      • toolmanmike

        toolmanmike Henchman #2 Staff Member FBBO Gold Member

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        A doggy engine could be something as simple as a fuel filter. That carb looks like a Quadrajet and it and the intake could have come from a Motor home or the like. ANd 440 intakes don't fit on 383's. You have some sorting out to do.
         
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        • Cojohnso1

          Cojohnso1 Well-Known Member

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          That's for sure. And I was thinking that carb and intake is unlikely from a 4.3? Definitely ID parts starting with engine. Something certainly isn't right.
           
        • chillbill

          chillbill Active Member

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          What other engines could fit a 440 intake? Where exactly should I look for for a number?

          6uRRU-ZbCGVRbQKeNUuWUsxiff0eXFfObgnZqTYsHCjXQfbB1CeBXMxWVpfF37gH38n9hyw=w1200-h900-no?authuser=1.jpg
           
          Last edited: Jun 23, 2021
        • chillbill

          chillbill Active Member

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          The driver's side of the block is the correct spot?
           
        • Cojohnso1

          Cojohnso1 Well-Known Member

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          Yes. Looks to be 383 just eyeballing. Newer air cleaner?

          upload_2021-6-23_19-42-52.png
           
        • diesel_lv

          diesel_lv Well-Known Member

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          General consensus on Google is that that Thermoquad manifold is 75-76. Get 2 opposing views though, one says 400 and one says 440. Both can't be right as one is low deck and one is raised. Intake won't fit both. But a Thermoquad never came on a 383.
           
        • fratzog lover

          fratzog lover Well-Known Member

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          That is a 440 intake from 75-76.
           
        • diesel_lv

          diesel_lv Well-Known Member

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          "The Mopar Dude" lists it as a TQ intake for a 400. You need to check the block itself for numbers. But, a 400 intake will fit the 383. But even parts guys make mistakes. Definitely need numbers from the block. Screenshot_20210623-175744_Chrome.jpg
           
        • diesel_lv

          diesel_lv Well-Known Member

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          "Moparts.org" confirms 75-76 400 B block.
           
        • QOTHL

          QOTHL FBBO Gold Member FBBO Gold Member

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          There should be a pad in front on the block that will say 440. Also, if that is a #'s car, the VIN should tell you what kind of engine is in it as well as the fender tag if it has one. I've had fuel leaks and it will make the car run crappy. Where's the leak coming from? You need to fix it because that and that plastic fuel filter are a fire hazard. I'm definitely no expert, but have had similar problems. Vacuum leaks will cause it to run lousy too. Make sure the carb bolts are snug. Original gas tanks can have crud in them that restricts fuel and can really F things up in your carb. Definitely check the plugs.
           
        • Kern Dog

          Kern Dog FBBO Gold Member FBBO Gold Member

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          No. do not do this.
          A vacuum secondary carburetor only feeds the engine what the engine needs. Ma Mopar built 318 4 barrel engines for the Diplomat and Gran Fury Police cars. Those even had Quadrajet carburetors. A stock 383 2 barrel engine can easily handle a 4 barrel carburetor.
          Several things can contribute to the sluggish performance.
          If the engine idles smooth but the car is a pig, you know that it is at least firing on all cylinders. The distributor advance weights could be stuck, the ignition timing could be at TDC or maybe 4 degrees before....That will make the car lazy. The advance curve (If functioning) could be painfully slow. The axle gearing could be the long legged 2.76 ratio...GREAT for 70 mph cruising but a poor match for a short stroke engine like a 383.
          My own "Jigsaw" Charger is a 383 model. I rebuilt the engine, raised the compression a bit and put in what people used to call a "RV cam". It idles with a slight lope. With a 3.23 gear, it would barely peel out. I swapped in a 3.91 and the car feels much different. It peels out great, chirps 2nd gear and actually rolls along nicely at 60-65 mph.
          Think about it.....Ignition and gearing.
           
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