TOKYO – Volkswagen AG surprises the Tokyo Motor Show with the unannounced Ecoracer concept car.

The carbon-fiber sports car is capable of 143 mph (230 km/h), yet achieves 69 mpg (3.4L/100 km) in normal European driving, thanks to its lightweight and 134-hp turbodiesel engine that uses spark plugs part of the time.

This is a first step toward homogenous combustion engines (HCCI)," says

Mathais Rabe, head of Group Research. "The car has solved many of tomorrow's problems today."

Both the Ecoracer and the expected Polo GTI cars are "ecologic, economic and as sporty as possible," he says.

The Polo GTI, featuring a 150-hp engine, goes on sale next spring in some European markets, priced at €18,950 ($22,619) in Germany.

VW Ecoracer concept sports car.

The Ecoracer coupe can be dismantled in steps, similar to the Citroen C3 Pluriel, becoming a roadster and then a speedster, as the roof, hatch and windscreen are removed incrementally.

The car has air scoops on the side to feed the centrally mounted engine, light-emitting diode headlamps and a keyless entry system that both unlocks doors and swings the roof up for easier ingress.

Although much of the concept is show-gimmick, it is a working vehicle that Volkswagen will use as a test bed. The car features a new double wishbone aluminum front axle and a next-generation 1.5L TDi direct-injection diesel engine.

While officially still under trial, VW says the engine meets future Euro V standards while making more than 184 lb.-ft. (250 Nm) of torque at between 1,900 and 3,750 rpm. Compression ratio is 17.2:1.

The engine operates part of the time with a spark plug, and the rest of the time with compression-ignition, says Rabe, "a first step" toward HCCI.

Industry engineers expect HCCI will be more efficient than current diesel or gasoline engines.

The yellow Ecoracer is 148 ins. (376 cm) long, 69 ins. (175 cm) wide and only 48 ins. (122 cm) high. It weighs 1,870 lbs. (850 kg) and rests on a 98-in. (240-cm) wheelbase.