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). Honda's system works by deactivating a bank of cylinders, while the Chrysler Hemi shuts off opposing pairs.

Two issues to overcome with all of these systems is the unbalanced cooling and vibration of variable-displacement engines.

Variable displacement technologies

• General Motors V8-6-4 (Cadillac)
• General Motors Displacement on Demand (DoD) (GM has renamed this technology to "Active Fuel Management" to better get its function/purpose across to the buying public)
• DaimlerChrysler Multi-Displacement System (MDS) (for Chrysler)
• DaimlerChrysler Active Cylinder Control (ACC) (for Mercedes-Benz)
• Honda Variable Cylinder Management (VCM)

See also

• Saab Variable Compression engine