Carburetor CFM Calculator

Carburetor CFM Calculator is a handy tool for all vehicle enthusiasts, mechanics, and the like. It’s an ingenious device that helps you avoid damaging your engine by facilitating the creation of an ideal air-fuel mixture. So, the million-dollar question is, do you know the requisite CFM for your carburetor? If not, how do you calculate it? This article is a comprehensive guide that addresses these queries.

How Does a Carburetor Work?

Have you ever wondered how birds and planes manage to stay afloat? This awe-inspiring phenomenon is primarily due to the Bernoulli equation, which also happens to be the operating principle of carburetors.

Fundamentally, a carburetor is a conduit that channels more air into the engine as you step on the accelerator. This tube navigates through a venturi, interlinked to the fuel intake.

Venturi and Valves

A venturi is a slightly constricted section of the pipe causing air to speed up while passing through it. According to the principle of conservation of mechanical energy, an increase in airspeed must coincide with a reduction in pressure. This decrease in pressure is sufficient to draw fuel from the fuel intake into the airflow.

Two valves regulate this air-fuel mix: the choke and the throttle. The choke is positioned at the top and determines the volume of air that can be sucked in. If the choke is closed, less air flows, reducing combustion in the engine due to insufficient oxygen.

The throttle, however, is located at the bottom. When this valve opens, it increases the air within the carburetor, consequently augmenting the amount of air and fuel in the engine. With ample oxygen to combust the fuel, more energy is released, driving the engine, and thus, the vehicle.

Working of the Carburetor CFM Calculator

The formula that our engine cfm calculator employs is:

Size of Carburetor = (Engine Size x Max RPM x Engine Efficiency) / 3456


  • Engine Size (CID): The size of your engine in cubic inches. It can also be specified in liters or cc (mL). For example, 1.2 L, 1400 cc.
  • Max RPM: Maximum revolutions per minute. You can conveniently obtain this information from the tachometer screen.
  • Engine Efficiency: A standard stock engine usually has about 80% efficiency. On the other hand, race engines range from 95% to 110%, and most rebuilt street engines have a volumetric efficiency of about 85%.

Usage of the Carburetor Calculator

Let’s take a practical example to understand the usage of our engine CFM calculator. Say we have a 340 in³ engine with a maximum RPM of 5,600 and efficiency of 80%. Here’s how the calculation will pan out:

V = CID Engine x Max RPM = 340 x 5,600 = 1,952,500 in³

For an engine with 80% efficiency, multiply the result by 0.80:

1,904,000 x 0.80 = 1,523,200 in³

Now, convert units from cubic inches (CID) to cubic feet per minute (CFM) using the division:

1,523,200 / 3456 = 440.74 CFM

This result elucidates how our carb CFM calculator operates!

Calculating the Carburetor Size for an Engine

Selecting the appropriate size of the carburetor for your engine is crucial to maximizing its performance. An undersized carburetor can starve the engine of fuel, while an oversized one can choke it.

Carburetors are classified based on the volume of air they can handle, measured in cubic feet per minute (CFM). So, how do you identify the perfect carburetor size for your engine?

The formula for calculating the size of the carburetor is:

Carburetor Size = (Engine Size x Max RPM x Efficiency) / 3456

For instance, find the ideal carburetor size for an engine with a displacement of 302 cubic inches, a max speed of 7,500 RPM, and 80% volumetric efficiency.

Carburetor Size = 302 x 7,500 x .8 / 3456

Carburetor Size = 524.31 CFM

That’s all there is to it!

In conclusion, the Carburetor CFM Calculator is an essential tool for anyone who wants to understand their vehicle better or optimize its performance. Make sure to use it and save your engine from potential damage!

Converter Tools

Recent Guides