# Carburetor CFM Calculator

> Calculate required carburetor airflow (CFM) based on engine displacement, RPM, and volumetric efficiency.

**Category:** Physics
**Keywords:** carburetor, cfm, engine, airflow, car, tuning, racing
**URL:** https://complete.tools/carburetor-cfm

## How it works

The tool calculates CFM using the formula CFM = (Engine Displacement × RPM × Volumetric Efficiency) / 3456. Engine displacement is measured in cubic inches, and RPM is the engine's rotational speed. Volumetric efficiency is a ratio that accounts for how effectively the engine draws in air, typically ranging from 0.85 to 1.0. The constant 3456 is derived from converting cubic inches to cubic feet and incorporating factors related to atmospheric pressure. The user inputs the engine specs, and the tool applies the formula to yield the required CFM.

## Who should use this

1. Automotive engineers designing performance engines for racing applications. 2. Mechanics tuning classic cars to ensure optimal fuel delivery. 3. Engine builders calculating airflow for custom builds. 4. Automotive hobbyists upgrading carburetors for improved performance in vintage vehicles.

## Worked examples

Example 1: An engine with a displacement of 350 cubic inches, running at 5000 RPM with a volumetric efficiency of 0.85. Using the formula: CFM = (350 × 5000 × 0.85) / 3456, we calculate CFM = 50.07. Thus, a carburetor rated around 50 CFM would be suitable for this engine.

Example 2: For a 302 cubic inch engine at 6000 RPM with a volumetric efficiency of 0.9, the calculation is CFM = (302 × 6000 × 0.9) / 3456. This results in CFM = 52.73. Therefore, a carburetor rated at approximately 53 CFM would meet the airflow needs of this setup.

## Limitations

1. The tool assumes a constant volumetric efficiency, which can vary with engine modifications, affecting accuracy. 2. The calculations can be imprecise for engines operating outside standard atmospheric conditions or at extremely high RPMs, where airflow dynamics change. 3. It does not account for additional factors like turbocharging or supercharging that can influence air intake requirements. 4. The formula may not be suitable for multi-carburetor setups, which have more complex airflow dynamics.

## FAQs

**Q:** How is volumetric efficiency determined for an engine?


**A:** Volumetric efficiency is typically determined through testing and is influenced by factors such as intake design, camshaft specifications, and engine speed. It reflects the actual amount of air entering the cylinder compared to the theoretical maximum.


**Q:** Can the tool be used for EFI systems as well?


**A:** While primarily designed for carburetors, the airflow calculations can provide insights for EFI systems; however, the tuning considerations differ significantly between carbureted and fuel-injected systems.


**Q:** What happens if I use a carburetor with a lower CFM rating than calculated?


**A:** Using a carburetor with a lower CFM than required can lead to insufficient air supply, resulting in lean fuel mixtures, decreased power, and potential engine damage due to overheating.


**Q:** Is the CFM calculation applicable to all types of engines?


**A:** The CFM calculation is primarily suited for naturally aspirated gasoline engines. It may not be directly applicable for diesel engines or those with forced induction without modifications to the formula.

---

*Generated from [complete.tools/carburetor-cfm](https://complete.tools/carburetor-cfm)*