Volkswagen is setting out to prove that green econo cars can be sporty too with its latest Polo Blue GT model that is making its world debut today at the 2012 Geneva Motor Show.

Based on the popular Polo hatchback that’s been on sale overseas for several years now, the Polo Blue GT combines performance with excellent fuel-efficiency by introducing Volkswagen’s new generation four-cylinder engine with cylinder deactivation technology.

This is the first production application of the advanced four-cylinder engine but you can bet more are just around the corner, including possibly some models delivered to the U.S.

The tiny engine displaces just 1.4 liters yet it delivers a reasonable 140 horsepower thanks to turbocharging and direct-injection technologies. It also comes matched with an engine stop-start system and brake energy regeneration.

The combined setup sees the Polo Blue GT go from 0-60 mph in under 8 seconds, top out at 131 mph, and return a fuel economy on the European combined cycle of 50 mpg. Note, these figures are for the manual. Opt for Volkswagen’s sweet seven-speed DSG dual-clutch and you’ll see economy rise to 52 mpg.

Volkswagen is the first automaker to introduce cylinder deactivation as a fuel-saving technology in smaller engines, because they were previously only used in larger engines with six or more cylinders. Shutting down the second and third cylinders under low and medium load reduces fuel consumption in the European combined driving cycle by about 8 mpg. In constant speed driving at 31 mph in third or fourth gear, fuel savings are as much as 16 mpg. Even at 43 mph in fifth gear, fuel consumption is still reduced by 11 mpg.

The cylinder deactivation feature becomes active at engine speeds from 1,250 to 4,000 rpm, and at torque outputs from 18 to approximately 74 pound-feet--a broad swath of the operating map that includes nearly 70 percent of most driving states, according to Volkswagen’s own research.

When the driver presses the gas pedal, the two non-functioning cylinders are imperceptibly reactivated. All mechanical switchovers are completed within half a camshaft revolution, which takes between 13 and 36 milliseconds, depending on engine speed.

Thanks to an ingenious accelerator pedal sensor and intelligent monitoring software, the system can also detect non-uniform driving profiles, such as through traffic or in a sporty manner on a country road. In such cases, cylinder shutoff is disabled. A small indicator light in the dash tells the driver whether two cylinders are engaged or all four.

The new Volkswagen Polo Blue GT, which bridges the gap between the 105-horsepower Polo 1.2 TSI and the 180-horsepower Polo GTI, goes on sale in Europe this July. Considering the Polo range isn’t on sale in the U.S., there’s next to no chance this sporty and efficient Polo Blue GT will ever come.