Annular vs downleg boosters on carb

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  1. B3422w5

    B3422w5 Well-Known Member

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    Considering a new carb. AED
    The place i am looking at doing one can give me the “ look” i want( black carb, red boosters and metering blocks.
    I figured on a 950.
    They recommend an 850 with annular boosters. I know an 850 is generally “ bigger” than a 950. He said the 850 if he uses annular boosters will give me the signal i want.
     
  2. Krooser

    Krooser Reform School Graduate

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    What application?

    I have never used annular boosters on any carb...street or oval track. Gas or methanol.

    Everytime I have asked the reply has been the same...downleg.

    YMMV.
     
  3. B3422w5

    B3422w5 Well-Known Member

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    418 12.5 compression. Decent eddie heads. Middle of the road flat tappet(260@50) suitable gear and 8 inch vert
    Car will live between 5000 and 6600-6800 on the track.
    Maybe an honest 530-540 ish horse
     
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    • PRH

      PRH Well-Known Member

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      The whole “850/950” thing these days means next to nothing.
      You need to be talking Venturi diameter.

      The “old school” 850’s were physically bigger than the original 950’s.

      With what most carb shops start out with for bodies these days, that’s not usually the case anymore.
      Something like a Qft Q-950 is bigger than a Q-850....... same thing with a Race Brawler.
       
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      • justinp61

        justinp61 Well-Known Member

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        The 950 I ran had down leg boosters, so does the 1.59" BX4 currently on my car, both have been great. As Dwayne mentioned it's all about venturi diameter, IIRC the 950HP had a 1.38" venturi and the 850 was 1.56". From my understanding the annular booster will take away some cfm in the carb and probably why he told you it would give you the signal you want.

        I robbed the 950 to build the BX4, but if I can come up with metering blocks and a good 1.75" base plate I'm going to build the 950 to test against the BX4 in the spring.
         
      • PRH

        PRH Well-Known Member

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        You can still buy at least 3 different sized “950’s”.

        The original HP950- 1.375 x 1.750
        QFT style 950- 1.450 x 1.750
        Holley XP950- 1.600 x 1.750

        My “good” 4150 carb I had done 30 years ago by Norm at CFS.
        HP carbs didn’t exist yet, so modified std bodies were the way it was done.
        I sent him a new Holley 4781(850DP), and he worked it over and swapped out the boosters for annulars.
        It’s been a great carb.
         
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        • Baxter61

          Baxter61 Well-Known Member

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          Mix em up, annulars in the front and downleg in the back
           
        • Mattax

          Mattax Just the facts, ma'am FABO Gold Member

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          I have a carb like that. Can't wait to be done foolin with it. At WOT fuel distribution from each booster goes mostly to just two runners. So now I've got different things happening in half the cylinders. Does it run well? Yes, but its not ideal. If you're patient, very patient - I will be trying two other carbs over the next year. One of which is an unmolested version of the same carb. And I would like to take the mixed booster carb and send it to Mark Whitner to put anular boosters in all four...

          Shrinker talks about droplet sizes and some of how that relates to fuel choice and engine specifics in this thread:
          Motorsports Village • View topic - Dyno time

          I think the short answer is that it also depends on what the engine dvelopment and racing goals are...
           
        • Hysteric

          Hysteric Well-Known Member

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          He also said this:

          "To get smaller drops with a Holley is difficult, the first thing is to ensure that there is not large air bleeds creating slugging flow.
          Stepped boosters make smaller drops."
           
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          • Hysteric

            Hysteric Well-Known Member

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            After you've thought about that you can think about this statement:

            "Its been my experience that the droplet formation of the Holley style carby imparts a limit to the mechanical configuration of the engine. People often talk about engines as being air pumps but if you only consider them from that point of view you miss the interaction of the fuel and thats the real reason for an engine isnt it. its actually there to convert chemical energy into mechanical energy and to do that you have to follow the chemistry not just the air pump."

            That should confuse a few people......
             
          • AndyF

            AndyF Well-Known Member

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            You don't need annular boosters in a drag car 4150 carb. They can help out a lot in a street/strip car since you can pick up a ton of bottom end torque with the annular boosters but the downleg boosters typically make a bit more top end power. If you running down the track between 5000 and 6800 RPM then I think a down leg booster would work the best. Best place for annular boosters in a 4150 carb would be a big venturi carb with a big cam in a street engine. In that situation the annular boosters will be a good crutch. I've seen dyno tests where the annular boosters will add 50+ ft-lbs at part throttle over a downleg booster. But by the time you get to 5000 rpm the difference is gone.
             
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            • Hysteric

              Hysteric Well-Known Member

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              Where at part throttle? 50+ ft-lbs sounds like a lot. Was it a case of just bolting the carbs on and seeing what the difference was or were both carbs set up correctly for an apples to apples comparison.
               
            • PRH

              PRH Well-Known Member

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              My personal experience from years of foot brake bracket racing is, the annular boosters allow you to run a large Venturi carb and still end up with a combo that leaves hard and is easier to tune for a nice clean hit.
               
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              • B3422w5

                B3422w5 Well-Known Member

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                kinda what AED said.
                That all said.... i can get that “ look” i wanted by the new color scheme holley “ race brawler” 850 has, and lots cheaper.
                They now come black with red metering blocks. Not sure how good of race carb it is, and it comes with downlegs.

                https://www.opgi.com/air-fuel-deliv...MI_IPb8b7I7AIVN_fjBx2SJgZNEAQYBiABEgIhqPD_BwE

                any thoughts Dwayne, with what i am doing?
                Gonna keep my 950 that is known good just to be safe
                 
              • AndyF

                AndyF Well-Known Member

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                Here is a Hot Rod article where they dyno test annular vs. dogleg: Annular Vs. Dogleg Carburetor Showdown - Car Craft Magazine

                I ran the same tests with my race 470 and saw similar results. The annular boosters work really well in cold weather. Not that that matters much for a race engine but the difference in torque can be significant. Just has to do with how well the booster shears the fuel. I don't know if any of this would matter in your application or not. You would have to test it to find out. The carb I used on my 470 was a Quick Fuel 1050-AN. Out of all the carbs I tested it worked the best on the dyno. I never used that carb in a car so I don't know how it drove.
                DSC_9558 (Large).JPG
                 
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                • 68 HEMI GTS

                  68 HEMI GTS Well-Known Member

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                  I built a 1050AN 4150 carb, worked real well on my 511. Ran 10.90’s and had excellent street manors.

                  D12663F1-E0AE-4015-BB63-222CE29E56E0.jpeg
                   
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                  • 512Stroker

                    512Stroker We are all here because we are not all there.

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                    OK why would you want to replace a "known good" carb?
                     
                  • B3422w5

                    B3422w5 Well-Known Member

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                    thought i said why several times in this thread. Trying to get the engine compartment to the level of the rest of the car. Maybe i am weird, but at this point in my life i not only want it to run as good as it should, want it to look good too
                    Want to find a carb to do just that. I certainly wont use something that will make it run worse...lol
                    Which is why i will keep my old carb if the new one wont get to or past its level performance wise, track testing it.
                     
                  • Hysteric

                    Hysteric Well-Known Member

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                    Were Both carbs 1050's?

                    Did you record where they both began to flow on the primary boosters?

                    Did you measure the Vacuum in both dyno runs?
                     
                    Last edited: Oct 22, 2020
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                    • gzig5

                      gzig5 Well-Known Member

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                      Are the body, bowls, plates that make up your current carb made of aluminum? If so, you can srip them down and have them anodized about any color you want for probably $100-150 or so. There are a lot of anodizers out there that do small jobs.
                       
                    • B3422w5

                      B3422w5 Well-Known Member

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                      thought about that. More trouble than i want to fool with.
                      Having an extra carb wont be such a bad thing to have laying around as a spare.
                       
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                      • MOPAROFFICIAL

                        MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                        They do is they say they can add some crispness to a single plane setup as well.
                        They are bigger and they take up room so if it really is an 850 it probably really isn't an 850 after those boosters went in was what all used to think because If remember right the 830 was an example of it
                         
                      • Mattax

                        Mattax Just the facts, ma'am FABO Gold Member

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                        Without a hp vs rpm graph, the torque difference is still a darn good indicator of which setup will be quicker.
                        After all no one spends any time to speak of at peak except maybe standing mile and high speed TSD events.
                         
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                        • MOPARMAGA

                          MOPARMAGA FABO Gold Member FABO Gold Member

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                          I believe its the older classic hp's are the carbs where 950 has a 750s smaller bore with 1.75 throttle plate. The velocity on those carbs is very good. Newer 950s flow honest 950 or more. It's been a while since I looked at them but I think a newer 950 with annular boosters is a great carb but will hurt flow at top end
                           
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