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Sizing A Motorcraft / Autolite 2100 Carburetor

Discussion in 'Early CJ5 and CJ6 Tech' started by Dauntless1971, May 11, 2019.

  1. May 11, 2019
    Dauntless1971

    Dauntless1971 Member

    Bend, OR
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    Oct 22, 2004
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    Now that I have a four barrel air cleaner to use. I am considering picking up a 2100 carburetor so I can just drop the air cleaner on my 225 Dauntless without any spacers or adapters. Best as I can tell a 1.08 model flows 287 cfm which is the same as the stock Rochester. I see the 1.02 venturis off a 1966 289 Mustang is 245 cfm yet it produced 200 horsepower. And a 1.14 sized venturi model flows 300 cfm. If you were trying for more hp I suppose the 1.14 might be appropriate. Then again the smaller carburetor might carry a higher vacuum. Have better low speed throttle response, but still able to produce enough cfm's to run a 225 properly.
     
  2. May 11, 2019
    colojeepguy

    colojeepguy Colorado Springs

    At the foot of...
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    I'd stick with the smaller one for a 225
     
  3. May 11, 2019
    Norcal69

    Norcal69 Out of the box thinker 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Northern California
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    1.08 is pretty much the go to unless your turning some serious rpm.
     
  4. May 11, 2019
    duffer

    duffer Rodent Power

    Bozeman, MT
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    I think any of those would work but don't think I would put on one that flowed less than the 2G.
     
  5. May 11, 2019
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    I would take any CFM figures I read for these OEM carbs with several grains of salt. These OEM carbs were never sold as anything but factory replacement carburetors, so specifications were never published. And IMO the CFM ratings for aftermarket carbs are mostly advertising copy ... I presume the 2100 CFM numbers that you read somewhere were determined by comparing relative sizes of the venturis of these OEM carbs and some aftermarket CFM rating. No better than a WAG IMO.

    The size of the venturi determines the velocity of the air flow through the throat of carb, and the velocity powers the movement of gasoline by the Bernoulli effect. This restriction of flow also creates a pressure differential (vacuum) which the carburetor uses to do work to meter the fuel. Too big a hole, too low a vacuum and there is not enough power to control the fuel. The flip side of this is too small a restriction, which provides precise fuel control but limits the amount of fuel-air charge that can be drawn into the cylinders at WOT.

    You could use a flow bench and plot the vacuum and CFM of the carbs in question, and get some more quantitative idea of relative fuel delivery, but I don't think that will inform you about fuel control.

    A too-big carburetor can run fine, as long as you are willing to sacrifice precise fuel control. This means too rich a mixture too much of the time. I have never seen or heard of a 1.02" 2100 - sure you aren't reading about the rare 260/289 4100 Motorcraft? I understood the 1.07" venturi 2100 is the smallest of the venturis offered in the 2100, and this carb was used on thousands of Ford small block V8s. These engines are 30-35% larger than a 225. It's also a very popular carburetor to replace the Carter BBD on the 232 and 258 AMC sixes. Other members here have used this carburetor on their 225s with good success. I think this is a better indicator than some unreliable CFM numbers from the net somewhere.

    BTW EFI can use a much bigger venturi area than a carburetor. An EFI system uses electricity to meter fuel, and only relies on vacuum as a sensor input to the computer. No need to squeeze work out of the engine vacuum...
     
    Last edited: May 11, 2019
    Dauntless1971 likes this.
  6. May 11, 2019
    Chilly

    Chilly Active Member

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    Go small. Its a small engine. And if youre turning consistent high revs with a 225 youre doing it wrong.
     
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