Enter your Engine Displacement (CID), Maximum RPM, Volumetric Efficiency, Engine Type, and Carburetor Type into the Carburetor CFM Calculator to find your Required CFM, along with a Recommended Range (Min/Max) and Airflow at Peak HP — so you can pick a carb that actually feeds your engine right.
Required CFM
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Recommended Range (Min)
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Recommended Range (Max)
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Airflow at Peak HP
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The CFM requirement depends on your engine displacement, maximum RPM, and volumetric efficiency. Use the formula: CFM = (CID × RPM × VE) ÷ 3456. A typical 350 CID engine at 6000 RPM with 85% efficiency needs about 525 CFM.
Vacuum secondaries open based on engine demand and provide better street drivability and fuel economy. Mechanical secondaries open at a preset throttle position and are better for racing applications where maximum airflow is needed immediately.
Yes, an oversized carburetor can hurt performance by reducing air velocity, causing poor throttle response, and poor fuel atomization. This leads to reduced low-end torque and poor fuel economy.
Volumetric efficiency is how well your engine breathes compared to its theoretical maximum. Stock engines typically achieve 80%, mild performance builds 85-90%, and race engines can exceed 100% with forced induction or advanced port work.
2-barrel carburetors are better for fuel economy and low-end torque in smaller engines. 4-barrel carburetors provide better high-RPM performance and are preferred for performance applications and larger displacement engines.
Street engines need smaller CFM for better drivability, while race engines can handle larger CFM for maximum power. High-performance street engines fall in between, requiring a balance of power and street manners.
An undersized carburetor will restrict airflow at high RPM, limiting peak horsepower. However, it may provide better throttle response and fuel economy at low speeds compared to an oversized carburetor.