In an unusual move aimed at boosting fuel economy, General Motors plans to make its V-8 truck engines use only four of their cylinders part of the time, starting with 2004 models in '03. GM sells at least 1 million V-8 trucks a year.
Lighter weight improves fuel economy, acceleration and braking.
Its operation was jerky, reliability iffy. GM pledges no repeat of that. Displacement on demand is a simpler system, controlled by more powerful and more sophisticated electronics, notes Allen Rayl, the engineer developing the electronic controls. The new system uses the engine control computer to halt fuel to four of the engine's eight cylinders, and uses a hydraulic system within the engine to uncouple valve lifters and keep the valves from opening in those four cylinders. Keeping the valves closed allows the unneeded pistons to move easier in the cylinders, and not become a drag on the four working pistons.