Carburetor CFM Calculator
Find the perfect carb size for your street or race engine.
e.g., 302, 350, 454
Redline where power peaks
Recommended Size
0
CFM
Suggest looking for carbs in the range of:
0 - 50 CFM
0 - 50 CFM
Choosing the Right Carburetor
Selecting the correct carburetor airflow rating (CFM) is critical for optimal engine performance. The goal is to provide enough air for maximum power without sacrificing low-speed throttle response.
Bigger isn't always better
Many enthusiasts make the mistake of buying too large a carburetor. A carb that is too big reduces the air velocity through the venturis, which weakens the vacuum signal needed to pull fuel into the airstream. This results in "bogging" when you step on the gas.
Volumetric Efficiency (VE) Explained
- 75% - 80% (Stock Engines): Standard factory engines with stock intake, exhaust, and camshafts.
- 85% - 90% (Street Performance): Engines with upgraded intakes, headers, and mild street cams.
- 95% - 105% (Race Engines): Highly modified engines with ported heads, aggressive cams, and high compression.
The Calculation Formula
The standard industry formula used to calculate CFM requirements for a four-stroke engine is:
CFM = (CID × RPM × VE) / 3456FAQ
What is CFM?
CFM stands for Cubic Feet per Minute. It measures the volume of air a carburetor can flow.
What happens if my carburetor is too big?
A carburetor that is too large (over-carbureting) causes poor throttle response, low-end bogging, and difficulty tuning, as air velocity through the venturis drops too low.
What is Volumetric Efficiency (VE)?
VE is ratio of the actual volume of air drawn into the cylinder to the theoretical maximum volume. Stock engines are 75-80%, street performance 85-90%, and race engines 100%+.
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