Variable Displacement

Variable displacement is a technology that has been widely used since 2004 since its debut in the 5.7 liter Hemi V8. Four cylinders are shutoff and do not contribute to the combustion process and the other four cylinders continue working to power the vehicle. The Variable displacement technology is very clever as it deactivates a certain number of cylinders (depending on the number of cylinders an engine has and the setup of the variable displacement) in a powerful engine when all the power is not demanded by the driver. 

Under normal driving conditions the driver does not use full throttle and does not demand peak performance from the engine. This means that all the cylinders are functioning without any purpose, wasting fuel and creating added pollution. By deactivating a certain number of cylinders under partial throttle fuel economy increases and the engine does not waste energy in operating more cylinders for no purpose. When the driver wants more power all of a sudden, say to overtake another vehicle, the driver depresses the throttle further and all the cylinders start functioning, the engine generates more power and the car can accelerate faster. When the driver slows down and drives normally and does not require all the power from the engine a certain number of cylinders are shutoff. 

Different manufacturers have given different names to their variable displacement technology. Chrysler calls theirs Multi-Displacement, Mercedes Benz calls theirs Active Cylinder Control, General Motors calls theirs Active Fuel Management, Honda calls theirs Variable Cylinder Management amongst others.