In this Carburetor CFM Calculator, we will show you how to find the required airflow for your engine in just a few seconds.
We will also help you understand what CFM is, the CFM formula, and why it matters for engine performance.
What is CFM?
How to calculate CFM for your engine? Find all the answers here!
We’ll also cover real-world applications of CFM, show you a step-by-step solved example, and provide a handy reference table so you can make quick and accurate calculations for your engine.
Carburetor CFM Calculator
Use this calculator to find the CFM required for your engine.
1. Formula Explanation
The Carburetor CFM (Cubic Feet per Minute) tells us how much air the carburetor can flow into the engine per minute. The formula is:
CFM = (Engine CID × RPM × Volumetric Efficiency) / 3456
- Engine CID: Cubic Inches of Displacement of your engine.
- RPM: Maximum revolutions per minute your engine runs at.
- Volumetric Efficiency (VE): How efficiently your engine fills with air (typically 70-100%).
- 3456: A constant to convert the units correctly.
2. Real-World Applications of CFM
Choosing Carburetors
Select the right carburetor for high-performance engines.
Engine Tuning
Optimize airflow to maximize engine power output.
Comparing Engines
Compare airflow requirements for naturally aspirated vs supercharged engines.
Aftermarket Intakes
Design high-performance intake systems for racing applications.
3. Problem Statement & Step-by-Step Solution
Narrative: You have a 350 CID engine, running at 5500 RPM with a volumetric efficiency of 80%. Determine the required CFM for the carburetor.
Step 1: List Known Values
- Engine CID = 350
- RPM = 5500
- Volumetric Efficiency = 80%
Step 2: Apply the Formula
CFM = (Engine CID × RPM × Volumetric Efficiency) / 3456
Step 3: Substitute Values
CFM = (350 × 5500 × 80) / 3456
Step 4: Calculate
CFM = 154000000 / 3456 ≈ 512 CFM
Step 5: Conclusion
The engine requires a carburetor capable of 512 CFM for optimal performance.
Carburetor CFM Reference Table
| Engine CID | RPM | Volumetric Efficiency (%) | Required CFM |
|---|---|---|---|
| 250 | 5000 | 75 | 271 |
| 300 | 5500 | 80 | 382 |
| 350 | 5500 | 80 | 512 |
| 400 | 6000 | 85 | 590 |
| 450 | 6500 | 90 | 763 |
Note: This table provides reference values for common engine sizes and conditions. Always verify with actual engine parameters for precise tuning.
FAQs
What is CFM?
In simple words, CFM (Cubic Feet per Minute) tells you how much air your carburetor can flow into the engine in one minute.
Why is CFM important?
CFM affects engine performance. Too little airflow can limit power, and too much can waste fuel.
What is Volumetric Efficiency (VE)?
VE shows how efficiently your engine fills with air. It’s usually given as a percentage, like 70–100%.
Can I use this for any engine?
Yes! This calculator works for most naturally aspirated engines. Just input the correct CID, RPM, and VE.