Volkswagen has announced what it claims is the first four-cylinder engine with cylinder shut-off - and it'll be available in cars fitted with the 1.4-litre TSI engine from the beginning of 2012.
The idea, of course, is to reduce fuel consumption by temporarily shutting off two of the four cylinders under low to medium loads.
In fact, says VW, it reduces fuel consumption of the 1.4-litre TSI by an average of 0.4 litre per 100km. Add to that a stop/start function that switches off the engine altogether when it's idling in neutral and the savings add up to a claimed one litre per 100km.
VW development engineers achieved the biggest gains while running at constant, moderate speeds, saving nearly a litre per kilometre running at a steady 50km/h in third or fourth gears - which may not be very practical in the real world but will bring this engine inside the future EU6 emissions standard.
The cylinder shut-off works by sliding the camshaft sideways so that the cams don't activate the inlet valves on cylinders two and three, whenever the revs are between 1400 and 4000 rpm and torque is between 25 and 75Nm.
That, says VW, applies to nearly 70 percent of the driving distance in the EU fuel-economy driving cycle - and as soon as the driver boots it harder than that, the engine's middle cylinders chime in so smoothly the driver won't notice anything except the extra voomah.
The control unit also monitors accelerator-pedal movement to detect driving conditions; if the pedal makes constant small movements (as in driving in heavy traffic) or regular big ones (as in driving hard on a country road) the system won't activate.