Your vehicle's carburetor combines fuel with air so that your engine can run. It determines the precise ratio of fuel and air that mixes together. Too much fuel hurts mileage, floods the engine and can create smoke. Too much air can keep the engine from running at all or damage it permanently. The size of carburetor you must install depends on the engine's output. Larger engines and engines whose gears turn at higher speeds, need larger carburetors.
Multiply the engine size, in cubic inches, by the top engine speed, in revolutions per minute. If your car contains a 260 cubic inch engine and works at up to 3,200 RPM: 260 x 3,200 = 832,000.
Divide your answer by 3,456. 832,000 / 3,456 = 240.74.
Divide your answer by the engine's volumetric efficiency, typically estimated at 0.85. 240.74 / 0.85 = 283. This is your required carburetor size in cubic feet per minute.
