Carburetor CFM Calculator

How to Calculate Carburetor CFM

Calculating the appropriate Carburetor CFM (Cubic Feet per Minute) is crucial for optimizing engine performance. This calculator helps you determine the ideal carburetor size based on your engine's specifications.

What is the Formula?

The formula for calculating Carburetor CFM is:

\[ \text{CFM} = \frac{\text{Engine Size} \times \text{Max RPM} \times \text{Volumetric Efficiency}}{3456} \]

Where:

• CFM is the carburetor size in Cubic Feet per Minute
• Engine Size is the engine displacement in cubic inches
• Max RPM is the maximum engine speed in revolutions per minute
• Volumetric Efficiency is the efficiency of air flow into the engine (typically 0.80 to 0.85 for most engines)
• 3456 is a constant derived from air density and other factors

What are the calculation steps?

1. Determine your engine size in cubic inches
2. Identify the maximum RPM your engine will reach
3. Estimate your engine's volumetric efficiency (usually between 0.80 and 0.85)
4. Multiply these three values together
5. Divide the result by 3456
6. The final number is your recommended carburetor size in CFM

Example Calculation

Let's calculate the CFM for an engine with the following specifications:

• Engine Size: 350 cubic inches
• Max RPM: 5500
• Volumetric Efficiency: 0.85

Step 1: Apply the formula

CFM = (350 × 5500 × 0.85) ÷ 3456

Step 2: Calculate

CFM = 1,636,250 ÷ 3456 = 473.45 CFM

Therefore, the recommended carburetor size for this engine is approximately 473 CFM.

Diagram of Carburetor CFM

The following diagram illustrates how different factors contribute to the Carburetor CFM calculation:

This diagram shows how Engine Size, Max RPM, and Volumetric Efficiency combine to determine the appropriate Carburetor CFM. The larger these input values, the higher the resulting CFM will be.