1. What is Carburetor Flow Rate?

The Carburetor Flow Rate (CFM) measures the volume of air (in cubic feet per minute) that a carburetor can flow at wide-open throttle. Proper CFM sizing is critical for engine performance.

2. How Does the Calculator Work?

The calculator uses the 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 (1728 cubic inches per cubic foot × 2 for 4-stroke cycle)

Explanation: The formula calculates the theoretical air flow requirement based on engine size, speed, and efficiency.

3. Importance of CFM Calculation

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

4. Using the Calculator

Tips: Enter engine's maximum RPM, total displacement (sum of all cylinders), and realistic VE (0.85 for street engines, up to 1.1 for race engines).

5. Frequently Asked Questions (FAQ)

Q1: What's a typical VE value?
A: Street engines: 0.75-0.90, Performance engines: 0.90-1.00, Race engines: 1.00-1.10.

Q2: How does altitude affect CFM requirements?
A: Thinner air at altitude reduces actual CFM needs, though the calculation remains the same.

Q3: Should I round up or down when selecting a carburetor?
A: Generally round up to nearest available size, but consider engine use (street applications often benefit from slightly smaller carbs).

Q4: Does this work for forced induction?
A: No, forced induction requires different calculations as it moves more air than natural aspiration.

Q5: What about multiple carburetors?
A: Divide total CFM requirement by number of carburetors when using multiple units.