1. What is Carburetor CFM?

Carburetor CFM (Cubic Feet per Minute) measures the airflow capacity of a carburetor. Selecting the correct CFM 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:

• \( RPM \) — Maximum engine speed (revolutions per minute)
• \( displacement \) — Engine displacement in cubic inches
• \( VE \) — Volumetric efficiency (typically 0.8-0.9 for street engines)
• \( supercharger\ factor \) — 1.0 for naturally aspirated, 1.1-2.0 for forced induction
• 3456 — Conversion constant (1728 cubic inches per cubic foot × 2 for 4-stroke cycle)

3. Importance of Proper CFM Calculation

Details: Correct carburetor sizing ensures optimal air/fuel mixture across the RPM range. Too large causes poor low-RPM performance; too small restricts high-RPM power.

4. Using the Calculator

Tips: For street engines, use 85% VE (0.85). Race engines may use 95-100% (0.95-1.0). Supercharged engines should use boost pressure ratio (e.g., 1.5 for 7 psi boost).

5. Frequently Asked Questions (FAQ)

Q1: What's typical CFM for a 350ci V8?
A: At 6000 RPM with 85% VE: ~517 CFM naturally aspirated.

Q2: Should I round up or down to available carb sizes?
A: For street use, round down. For racing, round up. Most carbs can be adjusted ±5% of their rating.

Q3: How does altitude affect CFM requirements?
A: Higher altitudes need slightly less CFM due to thinner air, but modern carbs compensate automatically.

Q4: What about multiple carburetors?
A: Divide total CFM by number of carbs (e.g., two 300CFM carbs for a 600CFM requirement).

Q5: How important is VE in the calculation?
A: Critical. Stock engines ~0.75-0.85, performance ~0.85-0.95, race engines ~1.0+ with proper tuning.