Variable displacement

Variable displacement is an automobile engine technology that allows the engine displacement to change for improved fuel economy. Many automobile manufacturers have adopted this technology as of 2005, but it is not a new concept.

Most variable displacement systems work by turning off a bank of cylinders in a V engine, but the initial systems worked differently. Pioneered on Cadillac's ill-fated L62 "V8-6-4" engine, the original multi-displacement system turned off opposite pairs of cylinders, allowing the engine to have three different configurations and displacements. But the system was troublesome, and the technology was quickly retired.

No automaker attempted the same trick again until Mercedes-Benz experimented with their Multi-Displacement System V12 in the 1990s. It was not widely deployed until the 2004 DaimlerChrysler Hemi. Other systems appeared in 2005 from GM (Displacement on Demand in the Generation IV small-block) and Honda (Variable Cylinder Management on the J family engines). All of these later systems work by deactivating a bank of cylinders, rather than opposing pairs.

Two issues to overcome with all of these systems is the unbalanced cooling and vibration of variable-displacement engines. Turning off pairs of cylinders leads to uneven firing, a problem not present in bank-based systems. Both systems, however, can suffer from uneven cooling.

Variable displacement technologies

• General Motors V8-6-4 (Cadillac)
• General Motors Displacement on Demand (DoD)
• DaimlerChrysler Multi-Displacement System (MDS) (for Chrysler)
• DaimlerChrysler Active Cylinder Control (ACC) (for Mercedes-Benz)
• Honda Variable Cylinder Management (VCM)