Carburetor Sizing

Ted (2/8/2020)

The 112 would be the venturi size with the number actually representing 1.12”. The 1.08” venturi carbs were found on the smaller engines like the 289’s while the 1.12” venturi carbs were found on almost everything else from 352 thru 428 engines. The 1.19” venturi carbs were made in limited numbers in the late Fifties and are sought after for their larger venturi size.

Dave V (2/9/2020)

Ted, I read your carburetor test comparison article and see that the 112 carb tested somewhat acceptable on the 312. I also am running a 57 312 but with an Isky E4 cam and a basic Holley 600. Is it worth my time and effort to swap to one of these 112 carbs? The car is a 56 Victoria with a 5 speed OD. I'm more into low end performance than high end HP. Thanks Dave

Because the original conversation is taking place in the classifieds, I have taken the liberty of making a new post.

When it comes to picking a carburetor for an application, carburetor sizing is only one piece of the equation. Fuel atomization is a bigger consideration and much of that has to do with the emulsion channels and discharge nozzle design within a particular carb. Holley makes a multitude of 600 cfm carburetors with all of them varying to suit various applications. The same is true for the 1.08 and 1.12 Ford carburetors as those were tailored for specific applications. One of the big advantages to the older Ford/Autolite carbs were the annular discharge nozzles which provides much better fuel atomization at the venturies than the more common straight leg and drop leg discharge nozzles.

One of the big pluses to running a vacuum secondary carburetor is that the secondaries are demand driven meaning they only open the amount required for optimum performance. This means that by intentionally oversizing a vacuum secondary carburetor for an application, it will never be undersized as the secondaries will only open the amount required by the engine.

To prove a point, I put a 1050 cfm Holley with annular discharge nozzles on my E4 cammed and otherwise stock 272 and drove it around for awhile. Ran just fine but was obviously on the big side if the throttle was opened up fully at low rpm. That car currently has the 500 cfm Summit carburetor on it which is slightly undersized but is a good driver otherwise. For most warmed over Y’s, a vacuum secondary carburetor being sized at 750 cfm proves to be adequate for those rpm sprints up to 6000 rpms. Keep in mind that most four barrel carburetors if just being daily driven will be operating on the two primary barrels that equate to a cfm rating that’s smaller than just running a two barrel carburetor (the older three bolt two barrel carbs are excluded from this statement).

Lorena, Texas (South of Waco)

Author	Message
Ted	Posted 5 Years Ago
Co-Administrator Group: Administrators Last Active: 4 days ago Posts: 7.4K, Visits: 205.0K	Ted (2/8/2020) The 112 would be the venturi size with the number actually representing 1.12”. The 1.08” venturi carbs were found on the smaller engines like the 289’s while the 1.12” venturi carbs were found on almost everything else from 352 thru 428 engines. The 1.19” venturi carbs were made in limited numbers in the late Fifties and are sought after for their larger venturi size. Dave V (2/9/2020) Ted, I read your carburetor test comparison article and see that the 112 carb tested somewhat acceptable on the 312. I also am running a 57 312 but with an Isky E4 cam and a basic Holley 600. Is it worth my time and effort to swap to one of these 112 carbs? The car is a 56 Victoria with a 5 speed OD. I'm more into low end performance than high end HP. Thanks Dave Because the original conversation is taking place in the classifieds, I have taken the liberty of making a new post. When it comes to picking a carburetor for an application, carburetor sizing is only one piece of the equation. Fuel atomization is a bigger consideration and much of that has to do with the emulsion channels and discharge nozzle design within a particular carb. Holley makes a multitude of 600 cfm carburetors with all of them varying to suit various applications. The same is true for the 1.08 and 1.12 Ford carburetors as those were tailored for specific applications. One of the big advantages to the older Ford/Autolite carbs were the annular discharge nozzles which provides much better fuel atomization at the venturies than the more common straight leg and drop leg discharge nozzles. One of the big pluses to running a vacuum secondary carburetor is that the secondaries are demand driven meaning they only open the amount required for optimum performance. This means that by intentionally oversizing a vacuum secondary carburetor for an application, it will never be undersized as the secondaries will only open the amount required by the engine. To prove a point, I put a 1050 cfm Holley with annular discharge nozzles on my E4 cammed and otherwise stock 272 and drove it around for awhile. Ran just fine but was obviously on the big side if the throttle was opened up fully at low rpm. That car currently has the 500 cfm Summit carburetor on it which is slightly undersized but is a good driver otherwise. For most warmed over Y’s, a vacuum secondary carburetor being sized at 750 cfm proves to be adequate for those rpm sprints up to 6000 rpms. Keep in mind that most four barrel carburetors if just being daily driven will be operating on the two primary barrels that equate to a cfm rating that’s smaller than just running a two barrel carburetor (the older three bolt two barrel carbs are excluded from this statement). Lorena, Texas (South of Waco)
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Carburetor Sizing

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