It is a limited (900 units) version of the Impreza WRX STI for the Japanese market. It included engine, suspension, and body parts improvement over the regular model. The ball bearing on the turbine axle was modified to reduce friction, the ECU retuned for better response, and an intercooler water spray fitted. The cross member, suspension and power steering were also improved for better handling and body rigidity. An aluminum hood, laminar window glass, and a lighter battery helped to reduce weight.

Debuting at the Tokyo Auto Show in October 2007, WRX STI versions build further on the standard WRX cars. The STI available in Japan is fitted with the 2.0-liter EJ207 engine with twin scroll turbocharger generating 227 kW (308 PS) at 6,500 rpm and 422 N⋅m (311 lb⋅ft) of torque at 4,400 rpm. Export markets receive the higher-displacement 2.5-liter EJ257 unit with the single-scroll VF48 turbocharger rated at 221 kW (300 PS) and 407 N⋅m (300 lb⋅ft) of torque. The turbocharger directs air through a larger top-mount intercooler which has lost the red "STI" that was on previous generations. The STI (3,395 lbs) is heavier than the WRX (3,174- 3,240 lbs depending on trim) due to a more...