Carburetor CFM Calculator
Calculate the required CFM (cubic feet per minute) for your engine's carburetor
Calculate Carburetor CFM Requirements
Engine displacement volume
Maximum revolutions per minute
Standard stock engines: ~80%, Race engines: 95-110%, Rebuilt street engines: ~85%
Carburetor CFM Requirements
Formula: CFM = (Engine Size × Max RPM × Efficiency) / 3456
Calculation: (0.0 CID × 0 RPM × 80%) / 3456 = 0.0 CFM
Air per stroke: 0.0 in³ (4-stroke engine)
Carburetor Size Recommendation
Example Calculation
340 CID V8 Engine Example
Engine Size: 340 cubic inches (CID)
Maximum RPM: 5,600 RPM
Volumetric Efficiency: 80% (standard stock engine)
Step-by-Step Calculation
1. Air volume = 340 CID × 5,600 RPM = 1,904,000 in³/min
2. Apply efficiency = 1,904,000 × 0.80 = 1,523,200 in³/min
3. Convert to CFM = 1,523,200 ÷ 3456 = 440.7 CFM
Engine Efficiency Guide
Stock Engines
~80% efficiency
Standard factory engines
Rebuilt Street
~85% efficiency
Performance street engines
Race Engines
95-110% efficiency
High-performance racing
Carburetor Size Guide
200-400 CFM: Small engines, economy cars
400-650 CFM: Mid-size V8s, street performance
650-850 CFM: Big block engines, hot rods
850+ CFM: Racing engines, drag cars
Understanding Carburetor CFM and Engine Airflow
What is CFM?
CFM stands for Cubic Feet per Minute, which measures the volume of air that flows through the carburetor. This airflow is crucial for proper engine combustion, as it determines how much fuel can be mixed with the air for optimal performance.
How Carburetors Work
- •Air flows through a venturi (narrowed section)
- •Bernoulli's principle creates pressure drop
- •Low pressure draws fuel into airstream
- •Air-fuel mixture enters engine cylinders
CFM Calculation Formula
CFM = (CID × RPM × VE) / 3456
- CID: Cubic Inch Displacement (engine size)
- RPM: Maximum revolutions per minute
- VE: Volumetric efficiency (decimal)
- 3456: Conversion constant (in³ to ft³)
Note: The constant 3456 comes from converting cubic inches to cubic feet and accounting for the fact that a 4-stroke engine only draws air every other revolution.
Carburetor Sizing Considerations
Proper Sizing Benefits
- • Optimal fuel economy
- • Better throttle response
- • Maximum power output
- • Reduced emissions
- • Smooth idle and operation
Incorrect Sizing Issues
- • Too small: Power loss, lean mixture
- • Too large: Poor idle, rich mixture
- • Reduced fuel efficiency
- • Difficult tuning
- • Poor drivability