Engine CFM Calculator
Calculate the carburetor or throttle body airflow requirement (in CFM) for an engine based on displacement and maximum RPM. Used by engine builders and performance tuners to select correctly sized carburetors.
Last updated: October 2026
Required CFM
607.64 CFM
Formula below · 2 sources (holley.com, firgelliauto.com) · Updated Oct 2026
Compare with similar
About this calculator
A four-stroke engine's airflow at 100% volumetric efficiency is displacement × RPM ÷ 3,456 cubic feet per minute: a 350 cubic inch engine at 6,000 rpm can draw about 608 CFM. The 3,456 comes from the 1,728 cubic inches in a cubic foot, doubled because each cylinder takes in a full charge only every second revolution.
Correct for volumetric efficiency
Real engines rarely fill their cylinders completely. Most stock and street-performance engines run at about 75% to 85% volumetric efficiency (VE), while some race engines exceed 100% at certain points in the rev range. Multiply the result by your VE: at 85%, the 350 at 6,000 rpm needs about 516 CFM. The table below gives both figures for common engines.
Choosing a carburetor or throttle body
Use the RPM where the engine makes peak power, not the redline. A carburetor much larger than the engine needs lowers air speed through the venturis, which hurts fuel atomization, throttle response and low-speed drivability; one that is too small caps top-end power. Street engines usually run best near the VE-corrected figure, while race engines that live near peak RPM can use more. Camshaft, cylinder heads, intake manifold and whether the engine is supercharged all change the answer, so treat the result as a starting point.
Units
The result is in CFM. For metric engines, convert liters to cubic inches by multiplying by 61.02: a 5.7 L engine is about 348 cubic inches.
| Engine | At 100% VE | At 85% VE | At 80% VE |
|---|---|---|---|
| 302 cu in at 6,000 rpm | 524 | 446 | 419 |
| 350 cu in at 5,500 rpm | 557 | 473 | 446 |
| 350 cu in at 6,000 rpm | 608 | 516 | 486 |
| 383 cu in at 6,000 rpm | 665 | 565 | 532 |
| 454 cu in at 5,500 rpm | 723 | 614 | 578 |
| 454 cu in at 6,500 rpm | 854 | 726 | 683 |
How to use
Enter the engine displacement in cubic inches and the RPM where it makes peak power. The default, 350 cubic inches at 6,000 rpm, gives about 608 CFM at 100% volumetric efficiency; multiply by your engine's VE (about 0.80 to 0.85 for most street engines) to get about 486 to 516 CFM. A 383 at 6,000 rpm gives about 665 CFM before the VE correction.
Frequently asked questions
What size carburetor do I need for a 350?
At 6,000 rpm, a 350 cubic inch engine flows about 608 CFM at 100% volumetric efficiency, or about 486 to 516 CFM at the 80% to 85% typical of street engines. Most street 350s therefore use carburetors in the 500 to 600 CFM range, depending on the cam and intended use.
What is volumetric efficiency?
It is how fully the engine fills its cylinders compared with their swept volume. Most stock and street-performance engines run at about 75% to 85%; well-developed race engines can exceed 100% near peak torque because of intake and exhaust tuning.
Why is 3,456 used in the formula?
There are 1,728 cubic inches in a cubic foot, and a four-stroke engine fills each cylinder once every two revolutions, so displacement × RPM is divided by 1,728 × 2 = 3,456 to get cubic feet per minute.
Related calculators
Sources & references
Think a result is wrong? Report a problem with this calculator.