The 2007 Impreza lineup is headlined by the high-performance WRX STI. The WRX STI is based on the Impreza WRX platform, but is uniquely engineered to provide even higher levels of acceleration, handling and braking performance that challenge the world's best sports cars.

The WRX STI draws motorsports technology directly from Subaru expertise in FIA 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.

In its sleek - and highly functional - exterior design, the Impreza WRX STI leaves no doubts about its performance attitude. The scoop in the aluminum hood feeds outside air to an intercooler that is significantly larger than the intercooler used on WRX models. The dual-plane rear spoiler - inspired by the Impreza World Rally Car - helps reduce lift and improve stability at high speeds. Front and side aerodynamic underbody covers enhances high-speed track stability, and airflow is also managed via front side spoilers on the front bumper and STI-design aerodynamic side ground effects.

The WRX STI also features a roof vane spoiler that helps to better manage the airflow over the roof of the vehicle. To further improve the aerodynamic performance the STI is also equipped with a specially engineered rear diffuser that reduces the coefficient of lift of the rear of the vehicle.

The front fascia features a four-beam headlight system with new multi-reflector High Intensity Discharge (HID) headlights. Distinctive STI fog lamp insert covers add to the no-nonsense look. Large diameter Brembo® ventilated disc brakes are clearly visible between the spokes of the 17-inch lightweight aluminum-alloy BBS® wheels.

Turbo-Charged Power
The 2.5-litre horizontally opposed, turbocharged and intercooled 4-cylinder engine produces 293 horsepower at 6,000 rpm and 290 lb.-ft. of torque at 4,400 rpm. It's based on a specially reinforced semiclosed deck engine block with forged aluminum-alloy pistons, forged high-carbon steel connecting rods and sodium-filled exhaust valves.

The turbocharger produces 14.5 psi of maximum boost, and the large capacity intercooler uses a manually operated water spray feature to enhance intercooler efficiency during high-performance driving in warm weather.

Subaru's Active Valve Control System (AVCS) variable valve timing technology helps provide strong torque characteristics throughout the engine's operating range. Teamed exclusively with a 6-speed manual transmission, the engine can propel the WRX STI from 0-60 mph in under five seconds.

Power is transferred to all four wheels by a sophisticated Subaru Symmetrical full-time All-Wheel Drive system with Driver Controlled Centre Differential to optimize performance in all conditions.

Symmetrical All-Wheel Drive With Driver Controlled Centre Differential
The Impreza WRX STI is equipped with the brand's most performance-directed Symmetrical All-Wheel Drive system featuring Driver Control Centre Differential (DCCD) with a planetary centre differential. Set in automatic mode, the electronically managed continuously variable transfer clutch varies the front/rear torque distribution automatically, depending on driving conditions and driver input. The system determines the ideal power distribution in response to vehicle acceleration, deceleration, steering angle, cornering force and wheel slippage.

In manual mode, DCCD allows the driver to vary the front-to-rear torque distribution for different driving conditions. Using a small control wheel on the car's centre console, the driver can set the system to transfer as much as 59 per cent of available torque to the rear wheels to increase handling agility.

The driver selects manual mode with a console-mounted button and then turns a thumbwheel on the centre console to choose from among six levels of centre differential locking. Increasing the lock factor keeps more power at the front wheels, which the driver might want in certain driving conditions, on particular roads or to suit an individual driving style.

The DCCD system incorporates a torque cam type LSD inside the centre differential planetary gear. The torque cam activates the LSD according to the actual torque difference between the front and rear axles for an extra measure of stability, even before the vehicle exhibits signs of oversteer.

A helical-type limited-slip front differential and a new quick-acting TORSEN® limited-slip rear differential optimize power distribution side-to-side, helping to ensure that the inside wheels don't slip during cornering.

Competition-Bred Chassis
Subaru's extremely strong Ring Frame Reinforced body structure with a hydroformed front subframe provides the foundation for the high-integrity Impreza platform. The 4-wheel independent suspension inherits technology from the Impreza WRC competition car, but has been strictly optimized in the WRX STI for high cornering performance on paved roads.

Inverted struts used for the front and rear suspension increase bending resistance for quicker and more consistent performance under hard cornering. A rally-derived variation on the MacPherson-type strut, the inverted strut functions like a conventional shock absorber set upside-down and encased by another tube. The strength of the outer steel tube bears the brunt of bending forces acting upon the strut under cornering, rather than the internal piston rod. The piston rod operates in the lower portion of the strut tube rather than the upper section.

The secondary upper tube mounts to the inner fender where the piston rod would mount in a conventional strut. The piston's stroke remains consistent during hard cornering, helping to maintain the ideal tire-to-road contact pattern for increased traction and cornering power. A steel lower L-arm is new for 2007.

The standard BBS light-alloy wheels measure 17 x 8 inches and are equipped with 225/45 ZR17 Bridgestone Potenza RE070 ultra high performance summer use tires.

The quick-ratio steering system is 2.6 turns lock-to-lock, and the steering rack uses a cannon mount for greater rigidity and improved on-centre response. A damper valve helps reduce the kickback that this increased rigidity might cause.

Brembo® Brakes with Super Sport ABS
Subaru equipped the Impreza WRX STI with one of the most advanced and performance-optimized braking systems on the market today. The powerful Brembo® Performance Brake System employs ventilated 4-wheel disc brakes to help ensure stopping power and consistency commensurate with the vehicle's high performance capability. The front discs are 323mm (12.7 inches) in diameter and 30mm (1.2 inches) thick with 4-piston, fixed-position calipers. The rear discs are 313mm (12.3 inches) in diameter and 20mm (0.8 inches) thick, and use 2-piston, fixed-position calipers.

A combination of Electronic Brake-force Distribution (EBD) and Super Sport Anti-lock Braking System (ABS) helps to reduce stopping distances and understeer compared to conventional ABS systems. EBD provides precise control of braking pressure between the front and rear wheels based on the vehicle load to improve stability and stopping distances. Conventional ABS systems control the rear wheels as a pair, reducing the braking force to both rear wheels. Super Sport ABS, using input from a lateral g-sensor, can control the braking forces at each rear wheel independently, optimizing the braking ability during hard cornering to help reduce understeer.

Performance-Directed Interior
The WRX STI conveys its performance attitude from the inside, as well. The driver grips a STI 3-spoke leather-wrapped steering wheel. Front seats designed for performance feature substantial side bolsters, integrated head restraints and embroidered STI logos. The seats are upholstered in unique perforated blue high-grip Alcantara® fabric with contrasting black knit bolsters, complemented by matching blue door trim and blue floor carpeting.

The WRX STI instrument gauge cluster places a 9,000 rpm tachometer in the centre, flanked by a 260 km/h (160 mph) speedometer, DCCD display, and fuel and temperature gauges. All three primary gauges feature sporty aluminum trim rings and red LED indicators. All the gauge needles swing to their maximum positions when the ignition is switched on, and then return to their normal positions.

Standard automatic climate control system integrates cabin air filtration. Making the ride even more entertaining is a new AM/FM/6CD/MP3/WMA premium audio system, which includes an in-dash auxiliary input for a portable audio source and pre-wiring for access to SIRIUS® Satellite Radio. An engine immobilizer security system is standard equipment.

Exceptionally Safe
Front seat head/chest side impact air bags (SRS) are standard, and all Impreza models for 2006 get the new Subaru Advanced Frontal Airbag system. The driver's side air bag deploys according to the driver's proximity to the steering wheel, as measured by a sensor on the seat track. In the passenger side front seat, a sensor module detects weight on the passenger seat - determining if it's occupied and, if so, by a child or adult - to control air bag deployment. As part of the system, the dashboard features a new airbag indicator light.

Front seatbelts use electrically triggered pre-tensioners and force limiters. A safety pedal system in all Impreza models is designed to prevent injury to the driver's lower limbs in the event of a serious front-end collision.