1. What is Carburetor CFM?

CFM (Cubic Feet per Minute) is a measurement of airflow capacity. For carburetors, it indicates how much air the carburetor can flow at wide-open throttle. Choosing the right CFM carburetor is essential for optimal engine performance.

2. How Does the Calculator Work?

The calculator uses the standard carburetor sizing formula:

Where:

• \( RPM \) — Maximum engine speed (revolutions per minute)
• \( displacement \) — Engine displacement (cubic inches)
• \( VE \) — Volumetric efficiency (percentage of theoretical maximum air flow)
• 3456 — Conversion constant to get CFM

Explanation: The formula calculates the theoretical air flow requirements of your engine at maximum RPM, adjusted by how efficiently your engine breathes (volumetric efficiency).

3. Importance of Proper Carburetor Sizing

Details: A carburetor that's too small will restrict airflow and limit power. One that's too large may cause poor throttle response and fuel economy. The ideal CFM provides optimal air/fuel mixture across the RPM range.

4. Using the Calculator

Tips:

• For maximum RPM, use your engine's redline or shift point
• Volumetric efficiency is typically 80-90% for street engines, 95-100% for race engines
• For forced induction applications, use higher VE values (100-130%)
• Round up to nearest available carburetor size

5. Frequently Asked Questions (FAQ)

Q1: What happens if my carburetor is too big?
A: Excessive CFM can cause poor low-end torque, sluggish throttle response, and decreased fuel efficiency due to insufficient air velocity.

Q2: What's typical VE for different engine types?
A: Stock engines: 75-85%, Mild performance: 85-90%, Race engines: 95-100%, Supercharged/turbo: 100-130%.

Q3: Should I round up or down on carburetor size?
A: Generally round up to the nearest available size, but consider your usage. Street engines can often use slightly smaller carbs for better drivability.

Q4: How does altitude affect carburetor sizing?
A: Higher altitudes require less CFM due to lower air density. Reduce calculated CFM by about 3% per 1000 feet above sea level.

Q5: What about multiple carburetors?
A: For multiple carb setups (like dual quads), divide the total CFM requirement by the number of carburetors.