1. What is Carburetor CFM?

Carburetor 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 drivability.

2. How Does the Calculator Work?

The calculator uses the standard CFM formula:

Where:

• \( CID \) — Engine displacement in cubic inches
• \( RPM \) — Maximum engine revolutions per minute
• \( VE \) — Volumetric efficiency (typically 0.85 for street engines)
• 3456 — Conversion constant

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

3. Importance of Proper CFM Calculation

Details: Correct CFM selection ensures proper air/fuel mixture across the RPM range. Too large causes poor low-end performance; too small restricts high-RPM power.

4. Using the Calculator

Tips: Enter engine displacement in cubic inches, maximum expected RPM, and estimated volumetric efficiency (0.85 for street, 0.90-1.0 for race engines).

5. Frequently Asked Questions (FAQ)

Q1: What's a typical VE for street engines?
A: Most street engines have VE around 0.85 (85%). Performance engines may reach 0.90-0.95, while race engines can exceed 1.0 with forced induction.

Q2: Should I round up to the nearest available carb size?
A: Generally yes, but stay within 10% of calculated CFM. For dual carbs, divide total CFM by 2.

Q3: How does altitude affect CFM requirements?
A: Higher altitudes require less CFM as air density decreases. Reduce calculated CFM by 3% per 1000 feet above sea level.

Q4: What about forced induction engines?
A: For boosted engines, multiply the calculated CFM by the boost pressure ratio (e.g., 1.5 for 7.5 psi boost).

Q5: Can I use this for EFI throttle body sizing?
A: Yes, the same CFM calculation applies to throttle body selection in fuel injection systems.