Panther said - "..snipped..... Is it not true that all of the air coming through my carburetor is uniformly mixed with fuel and air? Unless certain parts of the intake manifold are getting air from some other point of entry than the carburetor, I don't see how the AFR would be different in any cylinder. All of the cylinders are pulling air from the same point, which meters every cubic foot of air equally. .........
Carburetors meter all of the air coming into the manifold. If there is air in the manifold, it theoretically already has the correct amount of fuel metered into it."
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I think most sources would say the fuel provided by a carburetor is far from evenly distributed and thoroughly and uniformly mixed. Testing on the dyno may not simulate what acceleration does to the fuel in the carb, or the multi-phase mixture flowing into the engine.
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AMC Rambler's best effort to create equal AF ratio back in 1957 or so.
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" At this point, it hadn't yet become evident to dyno users that the use of in-car pieces (headers, ignition systems, cooling systems, etc.) on the test stand would be a logical step toward the need for linking engine testing with on-track performance. The importance of this fact was brought solidly home to me in the mid-'70s when sorting out some cylinder-to-cylinder mixture distribution fixes in a now bygone "Smokey Ram" intake manifold. Distribution fixes Smokey had determined on the dyno barely resembled what were required on the track."
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From the Hilborn INJECTION SITE -
"First it is important to keep in mind that the air and fuel have not mixed into a homogenous mixture in the venturi of the carburetor or in the runner of the intake manifold. A homogenous mixture is defined as a mixture whose physical properties are uniform throughout. Fuel in the manifold is not uniformly mixed as this only happens under the extreme heat and pressure contained in the combustion chamber. In reality, fuel in the intake tract uses air as a carrier; therefore, it is relatively easy for fuel to fall out of suspension, causing mixture distribution concerns."
And lots more.
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Here is a thread on a bulletin board showing some of the stunts that sometime have to be used to get carbs on "high performance" V8 manifolds to get the right amount of fuel to flow to the dry sections of the manifold.
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Post 10 here shows some of the carb assymetry applied by Chevrolet to improve the fuel distribution on the legendary L88 engine.