by Rick Smith
If someone told you that they were going to turn off half your engine while you were driving down the highway at over 50 miles an hour, you would probably tell them to "Get out!".
A GM Engineer did this to me recently and the result was underwhelming -- I didn't feel a thing! There was no jerkiness or hesitation. This vehicle had been specially equipped with an indicator light on the dash to indicate when half the engine wasn't running. Even when I watched it change, I sensed no appreciable difference in engine speed or sound. I stomped on the accelerator, the light immediately went out and the car accelerated normally. When cruising down the highway, at a steady speed, the indicator light went on to tell me that half the engine was off and that I was running on 3 cylinders. I sensed no change in engine sound or vehicle speed -- everything felt normal.
It turns out -- once your vehicle is moving down the road, it takes far less power to keep it moving -- in fact, half an engine is enough power. In a conventional vehicle, this "extra half" engine simply wastes fuel when cruising down the highway. GM has created "Displacement on demand" technology to accomplish this cylinder switching. The end result is a 10% increase in your fuel mileage, without any downside problems.
GM intends to roll out Displacement on Demand to a majority of their V-6 based vehicles during the next few model years. V-8 engines with this technology (Vortec 6000) will begin to appear in 2004.
In 2000, when I first looked at this Displacement on Demand technology, I recalled the similar, but problematic 4-6-8 technology used in some Cadillacs during the early eighties. Asking about this former technology, I found out that this older Cadillac technology had problems when transitioning a V-8 engine to run on only six cylinders. The four cylinder mode, however, worked quite well, even back then. Processing power has increased in past twenty years and there are some significant increases. The current engine computer has:
4 times larger data bus (32-bit vs. 8-bit) 25 times faster clock speed100 times the memory
of the 1981 controller.
Today, Displacement on Demand makes the process of shutting down half your engine smooth and unnoticeable. (Mercedes Benz also uses similar technology on their new V-12 models, which can also turn off half (six) of their cylinders, when cruising at highway and autobahn speeds.)
Location of the key mechanical components used in Displacement on Demand technology -- Solenoid Control Valve and Switching Roller Follower
Solenoid Control Valve Assembly
Switching Roller Follower
Actual GM Vortec 6000 V-8 engine -- one of the first GM V-8 engines to include Displacement on Demand in 2004
This terrific technology doesn't require any special effort on your part -- you drive normally. Displacement on Demand probably won't even be noticed by most consumers, other than through their pocketbooks, due to the improved fuel economy they will achieve.
Dated: December 1, 2002 -- (updated January 2003)