The Subaru Impreza WRX STI is a street-legal rally car, equipped with all-wheel drive, a 305-horsepower turbocharged engine, and plenty of racing-inspired performance upgrades. Based on the completely redesigned Subaru Impreza hatchback, which competes in the compact car class, the WRX STI is a product of the Subaru Tecnica International (STI) motorsports division of Subaru’s parent company, Fuji Heavy Industries. It exists so that Subaru can compete in the World Rally Championship (WRC), which requires that racing cars are based on production vehicles. As such, the WRX STI is equipped with many upgrades over other Imprezas – including the standard Impreza WRX – which are aimed at improving its acceleration, braking, and handling capability.

Here is a summary of major changes for the 2008 Subaru WRX STI:
• More power and torque; torque arrives at lower rpm
• Engine mounted slightly lower for a lower center of gravity
• Larger intercooler for turbocharged engine
• Variable valve timing added to exhaust camshafts
• Functional side vents to aid engine cooling
• SI-Drive throttle mapping technology
• New settings for Driver Controlled Center Differential (DCCD) all-wheel drive system
• Longer wheelbase and wider track for improved handling
• Double-wishbone rear suspension
• New stability control system with a performance mode that allows for a wider handling envelope while retaining the safety net
• Unique 18-inch wheels with 245/40 Dunlop SP600 performance tires
• Brembo brakes with larger rotors and pistons
• Super Sport ABS with Incline Start Assist
• Body shell is made of stronger steel than regular WRX
• Lighter curb weight than previous WRX STi
• Body modifications to reduce aerodynamic lift
• Larger interior with more rear leg room and larger cargo compartment
• Framed side window glass

The 2008 Subaru Impreza WRX STI is based on the Impreza WRX hatchback, but the company claims that other than basic structural elements, window glass, and some interior trim, the WRX STI is different in every way. Visual differences include a redesigned front end with a unique grille, HID headlamps with manual leveling, an aluminum hood with a larger air scoop, blistered front fenders, functional side vents for engine cooling, and functional brake cooling air intakes. At the rear, the WRX STI includes bulging quarter panels, special quad exhaust outlets, a revised rear bumper, LED taillights, and a prominent spoiler mounted at the top of the rear hatch. Five-spoke, 18-inch cast aluminum wheels are standard with forged aluminum BBS 18-inch wheels optional, each wearing 245/40 Dunlop SP600 performance tires, fronting Brembo-stamped brake calipers, and framing aerodynamic side skirts.

Inside, the WRX STI includes electroluminescent instrumentation with a 160-mph speedometer and a 9,000-rpm tachometer, sport-design front seats upholstered in Alcantara with leather bolsters, red accent stitching, a carbon fiber pattern in the leather on the steering wheel, and silver metallic interior décor. The STI comes standard with automatic climate control, a premium audio system, and a vehicle security system with engine immobilzer. A navigation system is optional, and it includes a vehicle information center, Audyssey Multi-EQ sound enhancement technology, and video jacks to accommodate portable gaming devices.

Mechanically, the Subaru 3,395-pound WRX STI is completely different from regular WRXs. Under the hood is a turbocharged, 2.5-liter horizontally-opposed four-cylinder engine (known as a Boxer engine, a design used primarily by Subaru and Porsche). This engine makes more boost than a standard WRX (14.7 PSI compared to 13.3 PSI) to generate 305 horsepower at 6000 rpm and 290 lb.-ft. of torque at 4000 rpm running on required 91-octane fuel. Subaru recommends 93-octane fuel for optimum performance. Power is delivered to an exclusive six-speed manual transmission, which routes motive force to all four wheels dependent on three factors.

First, the driver can program the WRX STI’s throttle mapping using Subaru Intelligent Drive (SI-Drive), which offers Intelligent, Sport and Sport-Sharp power deliver modes. Subaru says the more relaxed Intelligent mode is for commuting in traffic or driving in low-traction conditions, the Sport mode is best for everyday sporty driving, and the Sport-Sharp mode is for getting the power to the pavement as soon as possible.

Second, the driver can use the Driver Controlled Center Differential (DCCD) all-wheel drive system to choose between six manual differential locking settings and, new on the redesigned STI, three automatic settings. The new automatic settings are Auto, Auto (-), and Auto (+). Subaru says the Auto setting is the best for daily use, determining power distribution based on vehicle acceleration or deceleration, steering angle, cornering force, and wheel slippage. Auto (-) provides a rear bias to the power delivery and opens the center differential for improved steering feel, while Auto (+) tightens the limited slip differential for driving on slippery surfaces. The manual settings allow the driver to select a specific torque distribution up to 50:50 depending on driving conditions.

Third, the driver can select one of three settings for the WRX STI’s Vehicle Dynamics Control (VDC) stability and traction control system. The system features Normal and Off modes, and Subaru now offers a “Traction” mode that disengages the engine torque-reduction control and delays intervention by the VDC to create a wider performance and handling envelope for the STI without completely removing the safety net.

A Brembo Performance Braking System clamps bigger ventilated discs front and rear, and WRX STI has what Subaru calls Super Sport ABS, which controls braking force at each wheel independently based on lateral g-force, steering angle, yaw rate, and brake pedal pressure. Brake Assist and electronic brake-force distribution are included, and Subaru says the Super Sport ABS system can also help erase understeer. Unique suspension tuning is part of the STI package, and the car now comes with a compact double-wishbone rear suspension design. The quick-ratio steering features 2.8 turns lock-to-lock.

Subaru designs every vehicle with what it calls a Subaru Ring-Shaped Reinforcement Frame body structure, with the goal of providing superior crashworthiness. Additionally, the WRX STI features six standard airbags protect occupants, including dual front airbags, side impact airbags for the front occupants, and side curtain airbags. Additional safety features include the STI’s DCCD all-wheel drive, VDC stability control and Super Sport ABS systems.

J.D. Power and Associates says the standard Subaru Impreza competes against other compact sporty cars, most of which are coupes and convertibles. Because it is a low-volume, high-performance vehicle, the Impreza WRX STI’s most natural direct competitor is the Mitsubishi Lancer Evolution.