Subaru's new Impreza WRX goes on sale in Japan this week as a late 2007 model, and with it come greater anticipation for the high-performance STI version, which won't be officially revealed until the Tokyo auto show in October later this year.

The Subaru Impreza WRX five-door hatchback (known as the Impreza S-GT in Japan) features a turbocharged 2.0-liter version of the Subaru boxer-4, and it produces 248 horsepower at 6,000 rpm. When this car hits U.S. shores this fall as a 2008 model, it will have a 2.5-liter iteration of this engine that produces about 225 hp and 226 pound-feet of torque. In the UK, tight European emissions laws mean buyers won't be offered the WRX model when the hatch arrives there later this year.

Meanwhile, the "wilder", high-performance 2008 Subaru WRX STI expected to remain under cover until the Tokyo auto show already has a few key facts leaked.

The WRX STI draws motorsports technology directly from Subaru expertise in World Rally Championship (WRC) competition and is designed to appeal to the most serious driving enthusiasts. STI stands for Subaru Tecnica International -- the high-performance and motorsports subsidiary of Fuji Heavy Industries Ltd.

The highly anticipated STI is set to be powered by a tuned version of the 2.5-litre boxer engine turbocharged to produce more than 300hp and around 400Nm of torque, be mated to Subaru's existing six-speed manual box. A new automated manual, sourced from specialist firm Aisin, is expected to join the line-up when the latest Impreza is facelifted in 2009.

Subaru is making sure that the new Impreza can and will give its archrival, the 2008 Mitsubishi Evo X - which will feature an optional twin-clutch sequential-manual gearbox with steering-wheel-mounted shift paddles - a run for its money.

The top Impreza will offer a range of unique styling additions, including a specially developed bonnet, grille and a wide front bumper with big air intakes.

Flared wheelarches house smart 18-inch alloys, which will hide the existing STI's Brembo brake system. Buyers can expect to see minor tweaks to the all-wheel-drive system, and engineers have also taken the opportunity to tune the handling, thanks to a more compact double wishbone rear suspension set-up.

Inside, the new Impreza range boasts higher-quality trim, with the STI getting a pair of supportive bucket seats up front to boost its sporty appeal.

Subaru (maker of top of the line Subaru oxygen sensor), has also told Inside Line that a turbocharged boxer-4 diesel for the WRX is in the works and should be out by early 2009. The company is reportedly eager to drop a high-mpg diesel into the Forester and Impreza soon after the Legacy gets Subaru's first diesel next summer, so the WRX is part of the program. Sources from Subaru have also reportedly confirmed that the company is working on a five-speed automatic and a continuously variable transmission, and both these options could be offered as early as mid-2009.

Subaru is a Japanese car company and is the automotive division of Fuji Heavy Industries Co., Ltd. (FHI). It is currently an affiliate of Toyota Motor Corporation, with it owning 8.7% of FHI. They acquired that stake from General Motors, who bought 20% of FHI in 1999 to have an extended presence in international markets, and collaborate technologically with FHI.

FHI has recently set a new theme for Subaru cars that emphasizes Subaru's goal: Subaru offers a comfortable, pleasant drive for the driver and passengers; provides peace of mind and reliability; and extends convenience, utility and functionality.