Carburetor CFM Calculator
Find the carburetor airflow an engine needs.
Sizing a carburetor means matching its airflow (CFM) to the engine's appetite.
How the Math Works
The Carburetor CFM Calculator uses the formula CFM = (CID · rpm · VE) ÷ 3456 to determine the airflow an engine requires. Here, CID (cubic inch displacement) represents the engine's total volume, rpm is the revolutions per minute at maximum power, and VE (volumetric efficiency) measures how effectively the engine draws in air, typically between 70-85% for naturally aspirated engines. The constant 3456 converts cubic inches per minute to cubic feet per minute (CFM), accounting for unit conversions and the four-stroke engine cycle.
Practical Applications
To use this calculator, input your engine's CID (e.g., 350 for a 350 cubic inch engine), the RPM at peak power, and an estimated VE (often 80-85% for street engines). The result gives the required airflow in CFM, guiding carburetor selection. For example, a 350 CID engine at 6,000 RPM with 80% VE needs approximately 480 CFM, ensuring the carburetor matches the engine's breathing capacity for optimal performance.
Day-to-Day Use
This calculation is vital for car enthusiasts, mechanics, and DIY builders to properly size carburetors during engine rebuilds or modifications. By matching airflow to engine demands, users avoid issues like lean/rich mixtures, improve fuel efficiency, and enhance throttle response. It’s essential for tuning daily drivers, classic cars, or race engines, ensuring reliability and performance tailored to specific driving needs.
Worked example
350 CID at 6000 rpm, 85% VE → about 516 CFM.
FAQ
Bigger CFM is better?
Not always — an oversized carb hurts low-rpm response and economy.