1. What is Carburetor CFM?

CFM (Cubic Feet per Minute) measures a carburetor's airflow capacity. Choosing the right CFM carburetor is essential for optimal engine performance, fuel efficiency, and drivability.

2. How Does the Calculator Work?

The calculator uses the standard CFM formula:

Where:

• \( RPM \) — Engine revolutions per minute
• \( CID \) — Cubic inch displacement (engine size)
• \( VE \) — Volumetric efficiency (as percentage)
• 3456 — Conversion constant

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

3. Importance of Proper CFM Calculation

Details: An oversized carburetor can cause poor low-end performance and fuel economy, while an undersized carburetor restricts high-RPM power.

4. Using the Calculator

Tips: Enter your engine's maximum RPM, cubic inch displacement, and estimated volumetric efficiency (typically 80-90% for street engines, up to 110% for race engines).

5. Frequently Asked Questions (FAQ)

Q1: What's a typical VE for street engines?
A: Most street engines have VE between 75-90%. Performance engines may reach 95-100%, while race engines with optimized components can exceed 100%.

Q2: Should I round up to the nearest available carb size?
A: Generally, round to the nearest 50 CFM for street use. For racing, you might round up more aggressively.

Q3: How does altitude affect CFM requirements?
A: Higher altitudes require less CFM due to thinner air. Reduce calculated CFM by about 3% per 1000 feet of elevation.

Q4: What about forced induction engines?
A: This calculator is for naturally aspirated engines. For turbo/supercharged engines, use boost pressure to calculate corrected CFM needs.

Q5: How important is CFM for throttle response?
A: Smaller CFM carbs generally provide better low-RPM throttle response, while larger CFM carbs deliver more top-end power.