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How To Select The Right Carburetor Size

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Camo:
A selection guide of carburetor size  by Holley CLICK ME

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Volumetric Efficiency
Before you can determine the correct carburetor size for your engine, you must know its volumetric efficiency.
Volumetric efficiency is an indicator of how well an engine can breathe. The better an engine’s “breathing ability” the higher its volumetric efficiency. It is expressed as the ratio of the actual mass (weight) of air taken into the engine compared to the mass which the engine displacement would theoretically take in if there were no losses. The ratio is expressed as a percentage. It is quite low at idle and low speeds and varies with engine speed. Volumetric efficiency should be computed at the expected operating RPM or your engine application. Use the following examples as a guide to estimate the volumetric efficiency of your engine.

(A) An ordinary low-performance
engine has a volumetric efficiency
of about 80% at maximum torque.

(B) A high-performance engine has
a volumetric efficiency of about 85%
at maximum torque.

(C) An all-out racing engine has a
volumetric efficiency of about 95%
at maximum torque.............

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