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  • Fuel System: 2 barrel vs. 4 barrel carburetor

    I've seen several times where people have asked about the benifits, if any, of a 4 barrel carburetor over a 2 barrel.
    My recient story.

    One of the things I needed to do to prepare for getting my new(ish) Conestoga ready for daily driving duties, is to put a 4 barrel carbutetor on the 259 out of my ol 60 Lark. My current 59Lark wagon will have to forgive its Offenhauser manifold and Edelbrock carb. up for the original 2 barrel and manifold that were on it when I bought it. Yes, I still have it from almost 12 years ago..!
    The carb. is a 500cfm, "well..." used (up) version of the Edelbrock carb. Its seen many many miles on two different cars. The throttle shaft/base holes are shot. You have to tap the throttle to get the butterflyes to fully close for a proper idle..! I did buy a fresh one for after all the little problems that may crop up during the initial assembly into the Conestoga, (had a flat head 6), I know this one works well, fuel metering wise.

    Anyway, I rebuilt the original carburetor, cleaned the spiders out of the original manifold, even did a little (porting) radiusing of the hard corners from the throttle bore holes that lead into the runners..and made the swap about three weeks ago. So despite doing this backward from most of you, all details still directly apply.

    Now what many/some want to know -
    I'm not going to quote MPG here, just basic differences. Just note, that I took the time to make the Edelbrock carb. and engine happy together. I didn't just bolt it on and go. The the needles/metering rods are different, the springs that help control the rods are different thAn what comes in the stock carb.
    To start with, yes, "overall", the 500cfm AFB style carburetor has better driveability and gas milage in all circumstances thAn did the OEM 2 barrel (while on my 259, automatic trans., 59 Lark 2dr. wagon). Your results may vary.

    - The 4 barrel, good things -

    1. Part throttle sensetivity is much better thAn the 2 barrel.
    2. The around town drivability (see #1) is much nicer. Less throttle is used with the 4 barrel thAn the 2 barrel.
    3. Around town milage is better by a little over (1-1/2) mpg.
    4. The power is somewhat obviously better for getting on the freeways with all four barrels being allowed to open. The initial throttle response is better, just like it is for city driving, but when the secondaries start to open, you feel it.
    5. While not a long trip, I went to the Chino Air show yesterday (05.04.13), about a 45 mile one way drive the way I had to go, with about 80% of it freeway, and or faster two lane highway. The "passing" power it had....is now gone, even accelerating to change lanes...is gone. Sure, the engine/car will still accelerate, just not nearly as quickly. The smaller, primary throttle bores in the 4 barrel, again respond better to throttle pressure changes.
    6. Freeway milage is also better with the 4 barrel by a notable amount.

    - The 4 barrel bad things -

    1. Needing to "buy" the manifold, the carb., and an air cleaner.
    2. Need to adjust the throttle linkage, and if you have an automatic trans., you NEED to make sure the throttle pressure is correct, or very close. Shift points, etc.
    3. Had to make a new fuel line section from the fuel pump to the carb.

    --------------------------------------------

    - The 2 barrel good things -

    1. No money is required to install it....! (sorry).
    2. It keeps the engine looking stock.

    - The 2 barrel bad things -

    1. See 1 thru 6 above.

    This has been my experience over the last few weeks. As noted, MANY things can affect this swap, the state of tune of the engine, the transmission, the way the carb. and trans. throttle linkage is adjusted, etc., etc., even the way you drive. There may have been a coupla things I forgot here, but I can assure you, they were positive on the side of the 4 barrel carburetor.

    Mike
    Last edited by Mike Van Veghten; 05-05-2013, 08:41 AM.

  • #2
    Mike,
    Number 5. above is confusing. Are you saying, with the 4B, it has lost the passing power & road speed acceleration it had with the 2B? In other words, the power at those times is less with the 4B? If so, I would submit trying larger jets in the secondaries. I know yours is an Edlebrock, but some Holleys suffered from this malady straight from the factory, and larger secondary jets were the fix. My experience with AFB and their clones (Edlebrock) has been that the acceleration is much better than the 2B, under the conditions you cite above.
    Then too, if yours has worn primary shaft bores, it has a higher A/F ratio, which would lead to lean running under some conditions. A band-aid fix, would, again, be bigger secondary jets.
    Just saying.
    Last edited by JoeHall; 05-05-2013, 08:55 AM.

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    • #3
      I'm a 4-bbl fan all the way. Like MVV, I've seen nothing but good things from a properly sized and tuned install.

      Mike's #5 is confusing to me also, but then a vacuum secondary carburetor always has noticeable lag time between when the pedal hits the metal and the secondaries are actually with the program. Conversely, the 2-bbl has less WOT airflow, but it's all there all the time. Maybe it's the instant response he's referencing.

      I've mentioned it before, but I won't even try to tune a carb any more without a wideband 02 sensor and a direct digital readout. It's just magic; no guessing at plug readings, just read what's happening and change as indicated.

      jack vines
      PackardV8

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      • #4
        Not sure about 5. either. Any chance it's an automatic failing to hit passing gear?

        Comment


        • #5
          ***While not a long trip, I went to the Chino Air show yesterday (05.04.13), about a 45 mile one way drive the way I had to go, with about 80% of it freeway, and or faster two lane highway. The "passing" power it had....is now gone, even accelerating to change lanes...is gone. Sure, the engine/car will still accelerate, just not nearly as quickly. The smaller, primary throttle bores in the 4 barrel, again respond better to throttle pressure changes.***

          What's confusing ?
          The 4 barrel accelerates MUCH better thAn the 2 barrel at freeway speeds....in as simple a terms as I can think of. The longish #5 just included an explanation mixed in with the outcome.
          And...yes...the kickdown works properly. As one might guess from my explanation of the linkage...as noted in the #2 in the "bad" section, four barrel column, "adjust the linkage prpperly..!"

          And yes..."even" as worn as the my 4 barrel is...it "still" beats out the 2 barrel...hands down, in EVERY case...but returning to idle...!
          And while not mentioned earlier, I lightened the counter weights to fit the first engine the carb. was on. This lets the upper secondary butterflys open too soon on this engine, but with a combination of rpm, engine load, car speed and passing gear, during the right circumstances, everything works VERY well.
          I bought the newer adjustable "Thunder" version of this carburetor this time. This way...it's just a screw driver that's required to make the adjustment...not a drill motor..!

          Hope that helps some.

          Mike

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          • #6
            I think the confusing part was "the passing power it had...is now gone, even accelerating to change lanes...is gone." To me I thought that meant that you had that power with the 2 bbl but not with the 4bbl.

            Much clearer now, thanks! Also good to hear a positive review of the Thunder version. I had been wondering about those.
            Dave Nevin
            Corvallis, OR
            1953 Champion Deluxe Coupe
            Stud-e-venture blog

            Comment


            • #7
              Originally posted by Mike Van Veghten View Post
              While not a long trip, I went to the Chino Air show yesterday

              As much as I am happy for your report, I can't help thinking about where I can find your pictures from the air show. You took some, right?
              Hopefully you caught those SIX P-38s inflight...





              StudeDave '57
              StudeDave '57
              US Navy (retired)

              3rd Generation Stude owner/driver
              SDC Member since 1985

              past President
              Whatcom County Chapter SDC
              San Diego Chapter SDC

              past Vice President
              San Diego Chapter SDC
              North Florida Chapter SDC

              Comment


              • #8
                So Mike what exactly is it that is so much more adjustable on the Edelbrock 500 cfm Thunder Series AVS? 4 Brl. that is different from the very common older version "The Performer Series" 500?

                I just bought a new Thunder Series 500 from AutoZone their #1801 and it looks very much the same, have not tried it yet.
                StudeRich
                Second Generation Stude Driver,
                Proud '54 Starliner Owner
                SDC Member Since 1967

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                • #9
                  AVS stands for Air Valve Secondaries or Adjustable Valve Secondaries, depending on the source. The valve for the secondaries is screwdriver adjustable where on the standard Performer carburetor they are not.
                  Poet...Mystic...Soldier of Fortune. As always...self-absorbed, adversarial, cocky and in general a malcontent.

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                  • #10
                    The AVS has an adjustable spring loaded valve ABOVE the secondary venturis, where as the regular AFB and clones have the weighted flapper valve BELOW the venturies. If originality isn't a concern, they are a better choice . All other parts interchange (jets metering rods etc)
                    Bez Auto Alchemy
                    573-318-8948
                    http://bezautoalchemy.com


                    "Don't believe every internet quote" Abe Lincoln

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                    • #11
                      Very helpful and informative. Just picked up my 4 bbl manifold at South Bend and I have a remanufactured 55-58 Carter AFB to install on my 259 Commander. Any bad things to know about a Carter AFB?
                      Dave Warren (Perry Mason by day, Perry Como by night)

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                      • #12
                        Originally posted by warrlaw1 View Post
                        Very helpful and informative. Just picked up my 4 bbl manifold at South Bend and I have a remanufactured 55-58 Carter AFB to install on my 259 Commander. Any bad things to know about a Carter AFB?
                        Not many problems that I know of if the CFM's are small enough for a 259/289. the throttle linkage fits and the fuel line is in the right place.
                        Because this would not be a Studebaker AFB if it is a '58.

                        One of the main differences the Edelbrocks have is the middle Gasket has been eliminated by making those Two castings one piece to lessen leaks.
                        StudeRich
                        Second Generation Stude Driver,
                        Proud '54 Starliner Owner
                        SDC Member Since 1967

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                        • #13
                          The AFB was not introduced until 1957
                          I am sure you meant WCFB.
                          Robert Kapteyn

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                          • #14
                            Just what I read on the eBay ad. It said 55-58 Studebaker Carter 4 bbl. Guess I better look for some numbers on it. Thanks for the info. I'll get back to you with #s.
                            Dave Warren (Perry Mason by day, Perry Como by night)

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                            • #15
                              Yes, Robert, Carter WCFB. This will hopefully go on the 55 4 bbl manifold from Bob Petersen. Phil Harris sold me some carb to manifold gaskets and suggested I use two of 'em. It's going on a 259, automatic and I have a new bell crank and throttle rod. Any downside to these carbs? I'm familiar with vapour lock. Click image for larger version

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                              Dave Warren (Perry Mason by day, Perry Como by night)

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