1. What is CFM in Carburetors?

CFM (Cubic Feet per Minute) measures the airflow capacity of a carburetor. Selecting the correct CFM rating is crucial for optimal engine performance, as too large or too small can negatively affect power and efficiency.

2. How Does the Calculator Work?

The calculator uses the standard CFM formula:

Where:

• \( RPM \) — Engine revolutions per minute
• \( Displacement \) — Engine displacement in cubic inches
• 3456 — Conversion constant (1728 cubic inches per cubic foot × 2 for 4-stroke cycle)

Explanation: The formula calculates the theoretical maximum airflow requirement based on engine size and operating RPM.

3. Importance of Proper CFM Calculation

Details: Correct CFM selection ensures proper air/fuel mixture. Too large a carburetor can cause poor low-end performance, while too small restricts high-RPM power.

4. Using the Calculator

Tips: Enter your engine's maximum operating RPM and total displacement in cubic inches. For modified engines, use the RPM where you expect peak horsepower.

5. Frequently Asked Questions (FAQ)

Q1: Should I round up or down when selecting a carburetor?
A: For street engines, round down slightly. For racing applications where maximum power is desired at high RPM, round up.

Q2: What about volumetric efficiency?
A: This formula assumes 100% VE. For more accuracy, multiply the result by your engine's actual VE (typically 0.8-0.9 for street engines).

Q3: Does this work for forced induction?
A: No, forced induction requires different calculations as it moves more air than natural aspiration.

Q4: What's the typical CFM range for different engines?
A: Small 4-cylinders: 200-350 cfm, V8s: 500-750 cfm, high-performance engines: 750+ cfm.

Q5: How does carburetor size affect drivability?
A: Oversized carbs can cause hesitation and poor fuel economy, while undersized carbs limit top-end power.