Volumetric Efficiency
The ratio of the air volume drawn into an engine cylinder to the cylinder's actual swept volume.
Volumetric efficiency (VE) is a ratio that measures the effectiveness of an internal combustion engine's induction system. It is the volume of air-fuel mixture drawn into the cylinder during the intake stroke compared to the static volume of the cylinder. A naturally aspirated engine typically operates at 80% to 90% VE under normal conditions.
To improve volumetric efficiency, engineers tune the intake manifold runner lengths, use multiple valves per cylinder, and implement variable valve timing (VVT) to optimize airflow velocities. Forced induction systems (turbochargers and superchargers) compress the intake air, forcing more air mass into the cylinders and pushing volumetric efficiency well over 100%, resulting in significant power increases.
A drop in volumetric efficiency causes a corresponding loss of engine power and poor fuel economy. Common mechanical causes of low VE include a clogged engine air filter, a restricted exhaust system (such as a melted catalytic converter), worn camshaft lobes, or carbon buildup on the intake valves. Technicians use scan tool data (MAF and MAP sensor PIDs) to calculate and diagnose engine volumetric efficiency.