Subaru's compact Impreza sedans and hatchback wagons are available in a wide range of models for 2007, including a base model, the rugged Outback Sport wagon, the sporty WRX, and the very high-performance STI. Impreza 2.5 i and Outback Sport models come with a 173-horsepower, 2.5L flat four-cylinder engine with i-Active Valve Lift. WRX models step up to a 224-horsepower, 2.5L turbocharged flat-four with Active Valve Control, and top STI models gets a 293-horsewpower, 2.5L version of the WRX's turbocharged engine. 2.5 i, Outback Sport, and WRX models have either a five-speed manual or four-speed automatic transmission, while the STI comes only with a six-speed manual. All Imprezas have all-wheel drive; it powers all four wheels all the time and can transfer more power to the wheels with the best grip. Wagon models have a 60/40-split folding rear seatback for easily expanding the cargo area, while sedans get a trunk pass-through for skis. All Imprezas have front-seat head/chest side air bags standard, along with anti-lock brakes with electronic brakeforce distribution, and headrests for all three back-seat positions. Base 2.5 i models come quite well equipped, with air conditioning, cruise control, keyless entry, four-speaker CD sound, and power windows, locks, and mirrors. The Outback Sport model borrows rugged cues from the larger Outback wagon model, and includes gray lower body moldings and bumpers, 16-inch alloy wheels, halogen fog lights, a cargo power outlet, roof rails, and a rear bumper step. Both the 2.5 i sedan and the Outback Sport are available in a Special Edition, which adds additional equipment including automatic climate control and an upgraded sound system with CD changer. The rally-inspired WRX gets a sport-tuned suspension, high-performance brakes, and larger 17-inch wheels to handle the turbocharged engine's extra power. The WRX models get a slightly different headlight and taillight design for this year, and inside, bolstered sport seats, aluminum pedal pads, and a leather-trimmed shift knob complete the package. Automatic climate control and an upgraded sound system with CD changer are standard on the WRX. Two other WRX models are offered. The WRX Limited brings more luxury equipment, including leather-trimmed heated seats, heated mirrors, a windshield de-icer, and a moonroof. In the other direction is the stripped-down, track ready WRX TR, which opts for the base sound system, standard air conditioning, and fewer standard features. The top-performance STI, tuned by Subaru Tecnica International, the high-performance and motorsports division of Subaru's parent company, offers overall performance that rivals some of the world's top (and much more expensive) sports cars. The STI has a unique six-speed manual with carbon-plated synchronizers for the top gears, and a specially set-up version of Subaru's Symmetrical All-Wheel Drive system. The system's Driver Controlled Center Differential (DCCD) allows the opportunity to manually vary the split of power between the front and rear wheels, and a new mechanical limited-slip differential helps improve drivability and handling. STI visual cues include special ground effects, a roof vane spoiler and rear spoiler, underbody aerodynamic work, and wide-flare fenders. The STI also employs a Brembo high-performance braking system with Super Sport ABS, and the suspension is lowered nearly an inch compared to the WRX. There's also an STI Limited model, in a limited run of 800, which adds perforated leather seating, heated seats, a moonroof, and a "stealthy" appearance package.