Variable Displacement

Displacement On Demand isn't a new idea, but its time may truly have come. Today's quick-reacting microprocessors will allow DOD engines to smoothly activate and deactivate cylinders--without jerky power delivery or performance degradation.

Variable Displacement
One of the great technological hopes for truck and luxury-car producers dependent on larger, thirsty engines is variable displacement, or more accurately, cylinder deactivation. The idea is simple: Not all barrels need to be firing all the time. You may remember that Cadillac tried this in the early '80s, with its V-8-6-4. Though engine-management technology of the day wasn't yet up to the job, the concept has taken on new validity made possible by today's high-power microprocessors.

Delphi Automotive Systems engineers claim this tech trick could provide an 8-10-percent improvement in fuel economy. How? A full-size V-8 pickup cruising at highway speeds with an empty bed, for example, really only needs the muscle from four cylinders to maintain headway. So, fuel, spark, and valve actuation could be cut off from the inactive cylinder bores. You'll see these systems on GM trucks within a few years. Mercedes-Benz' S600 sedan and CL600 coupe are powered by an all-new 362-hp V-12 with active cylinder control, and officials claim the system helps the big motor return 20-percent-better fuel economy over the old V-12. At the same time, these premium Mercedes are capable of hitting 60 mph in less than six seconds, so there's no apparent performance penalty.