Volkswagen boosts Passat fuel economy with two-cylinder engine mode

The drive for inexpensive ways to boost the fuel economy of gasoline cars has led automakers to some strange places, from car shutters to transmissions with as many speeds as your bicycle. Most have shrunk their engines and added turbos to regain lost power; a few automakers have experimented with tiny three-cylinder engines.

But today, Volkswagen reached a new realm in fuel efficiency, revealing a concept version of its midsize Passat sedan capable of 42 mpg on the highway, the high mark for a car that size running a non-hybrid gasoline engine. Its secret? Running on just two cylinders as often as possible.

Cylinder deactivation — using electronics to shut off fuel and close the valves to a few cylinders, turning them into air springs — has been around for years in V-8s; the new Corvette Stingray turns into a V-4 at highway speed. Honda uses cylinder deactivation in versions of the V-6 Accord sedan, boosting its efficiency to 34 mpg.

But cutting off half of an inline four-cylinder poses some technical challenges. In a V-engine, it's easier to balance the loads; here, VW shuts off the inside two pistons. The 1.4-liter engine also uses turbocharging, direct injection and a stop-start system to further save fuel. While VW calls it a concept for now, it's likely to see production as fuel economy standards rise.