A Guide to Volumetric Efficiency and What It Means for Performance Engines

A Guide to Volumetric Efficiency and What It Means for Performance Engines

March 19, 2019

The term “volumetric efficiency” comes up a lot in discussions about internal combustion engines. However, it seems most people do not really understand what volumetric efficiency is and the effect it has on engine performance. Read on to learn more!

What is volumetric efficiency?

Volumetric efficiency is the amount of air that flows through the engine in comparison to the theoretical maximum. In short, it’s the measure of the fullness of the cylinders. Volumetric efficiency, commonly known as VE, is typically measured as a percentage. Drivers want their engine operating at 100 percent VE, as that means all the air has been trapped that the cylinder is designed to hold. The volume will always measure the same, but certain restrictions can reduce the mass of air and fuel in comparison to what it’s designed to hold. Things like the inertial tuning of the intake, cams, heads and exhaust can increase the volume. As a result, this increases the amount of the air and fuel available to be burned into power.

How is volumetric efficiency calculated?

VE is calculated using three different inputs: the engine RPM, the measured airflow and the engine displacement. From there, you can determine how much air the engine should be able to pump at a specific RPM, and then compare that to the amount of air that’s registered as entering the engine—the higher the percentage, the better the airflow. Additional factors such as the barometric pressure, humidity and even the outside air temperature can also affect the air density and the final percentage. Professionals recommend a VE of 75 percent or higher, but that number will vary drastically based on the different engine applications. For example, a V6 engine on an overhead valve engine could hit 75 to 80 percent VE, while a double overhead cam four-cylinder engine with improved airflow will likely register somewhere between 80 to 95 percent.

How VE relates to an engine’s dyno curve

As mentioned before, your vehicle’s VE can change based on the environment. An engine would operate at a higher VE in the dense air at sea level than in the thin air of the mountains. The key to optimum performance is to improve the VE by making improvements to the airflow. That’s where aftermarket parts like superchargers, nitrous oxide and turbos come in. These additions force more air into the cylinder and can push the VE over 100 percent when combined with properly turned fuel and ignition systems.

Improve VE with expert dyno tuning in Santa Rosa, CA

The professional auto technicians at Fine Line Imports can help you achieve maximum volumetric efficiency for the best vehicle performance. Our team specializes in Japanese auto repair, including Subaru and Nissan vehicles. We offer a complete range of aftermarket performance improvements, including custom-tailored engines, transmissions, drive-train rebuild packages, OEM services, comprehensive tuning packages and more. Stop by our shop today to learn more about optimizing your car’s VE, or call to schedule an appointment for dyno tuning service in Santa Rosa, CA!

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