Carburetor CFM Calculator

This sizes a carburetor to an engine using displacement multiplied by rpm, divided by 3456 for a four-stroke or 1728 for a two-stroke, and scaled by volumetric efficiency. Enter the displacement in cubic inches, litres or cc with the peak rpm and the efficiency you want to assume, and it returns the required airflow, the figure at a perfect 100 percent fill, the equivalent two-barrel rating and the first common four-barrel size that covers it. A second tab turns a carburetor rating you already have into the engine speed it can feed. Volumetric efficiency is an assumption rather than a measurement and it moves the answer proportionally, so the result names the figure it used and what a realistic one looks like.