1. What is the Holley CFM Formula?

The Holley CFM formula calculates the required carburetor size (in cubic feet per minute) based on engine RPM, displacement, and volumetric efficiency. It helps select the properly sized carburetor for optimal engine performance.

2. How Does the Calculator Work?

The calculator uses the Holley CFM formula:

Where:

• \( RPM \) — Engine revolutions per minute
• \( displacement \) — Engine displacement in cubic inches
• \( VE \) — Volumetric efficiency (typically 0.8-0.9 for street engines)
• 3456 — Conversion constant

Explanation: The formula calculates the theoretical air flow requirement of the engine at maximum RPM.

3. Importance of Proper CFM Calculation

Details: Selecting the correct carburetor size is crucial for engine performance. Too large causes poor low-end response, while too small restricts high-RPM power.

4. Using the Calculator

Tips: Enter engine's maximum RPM, total displacement in cubic inches, and estimated volumetric efficiency (0.85 is typical for street engines).

5. Frequently Asked Questions (FAQ)

Q1: What's a typical VE value for my engine?
A: Street engines: 0.75-0.85, Performance engines: 0.85-0.95, Race engines: 0.95-1.1 (with forced induction)

Q2: Should I round up the CFM value?
A: Generally round to nearest available carburetor size, but consider usage - street engines can often use slightly smaller carbs for better drivability.

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

Q4: What about forced induction engines?
A: For supercharged/turbocharged engines, multiply the result by your boost pressure ratio (e.g., 1.5 for 7.35 psi boost).

Q5: Does this work for multiple carburetors?
A: Yes, divide the total CFM requirement by the number of carburetors you plan to use.