MOUNT JUDEA, Ark. -- Tearing down a narrow canyon course etched into walls of granite, a street-legal rally car flows with the tight-cornered twisties on route 123, a two-lane slalom course wiggling through deep folds of the Ozark Mountains of northern Arkansas. To tell the truth, we're flying down this hairpin trail while working the leather-bound steering wheel and plying a six-speed gearbox with a turbo-charged and inter-cooled boxer-four engine whining and the speed-rated tires -- Dunlop SP Sports wrapped around BBS forged-alloy silver wheels -- bonding to blacktop at all four posts, thanks to the electronically controlled all-wheel-drive system.
These racy maneuvers are performed on a traffic-free course in the Ozarks simply to see what this vehicle can do. And, we discover, it can do a lot. We're talking pin-your-ears-to-the-seat accelerations and king-of-the-street speeds in a relatively lightweight five-door hatchback package patterned after World Rally Championship (WRC) race cars.
This turbo-charged five-door sports hatchback from Japanese automaker Subaru is called the Impreza WRX STI. It's based on the compact Impreza platform and derived from Subaru's WRX performance car but with more juice extracted from the engine and more sporty paraphernalia aboard to cede no street racer's challenge.
Those STI initials on souped up WRX signify Subaru Technica International, the motorsports division of Subaru and the force behind Subaru's trophy-collecting rally cars. What's a rally car? It's a race car usually of small scale with some stock equipment aboard but also a high-output engine and modifications for added safety like a protective roll cage and five-point racing harnesses for the two front seats.
Rally races pit a driver and co-pilot/navigator in a special race car against a stopwatch and detailed route maps, with daredevil competitors tearing across treacherous roads through cities and countryside, each vying to nail all checkpoints on time and beat the clock across a finish line. Beyond North America in countries around the world, automobile rally racing receives the kind of sports attention that football fans in the United States reserve for contests like the Super Bowl. And in the WRC Subaru has racked up many wins, thanks to the wily nature of Subaru rally cars spinning off the Impreza platform.
The 2009 WRX STI, also using the Impreza as its foundation, emulates those Subaru rally cars, only without roll bars or five-point safety harnesses aboard. The STI edition varies from a production model WRX in terms of powertrain and gearbox, with special mechanical equipment added to boost performance and handling, and specific body enhancements on a five-door hatchback package.
Special STI design features for the shell range from wide-body front fenders and rear quarter panels to functional brake cooling scoops up front and a spoiler mounted on the back gate, engine heat outlets cut into flanks and side moldings applied for aerodynamic ground effects. The contoured aluminum hood supports a functional air scoop just ahead of a raked windshield.
But everything about this vehicle revolves around the amazing engine tucked below the STI's front deck. The plant has four cylinders opposed horizontally and set perpendicular to the drive line, then linked with equal-length drive shafts so pairs of cylinders act like boxers jabbing at one another in counterbalanced movements that negate the typical in-line-four engine's vibrations.
Displacement increases to 2.5 liters for a die-cast aluminum block with aluminum cylinder heads and dual overhead camshafts (DOHC) plus Subaru's dual active valve control system (Dual AVCS) variable valve timing controls for both intake and exhaust valves. Thanks to the high-boost turbo-charger and a cross-flow inter-cooler aboard, the STI engine racks up some awesome muscle numbers. It makes 305 hp at 6000 rpm plus as much torque as 290 lb-ft at 4000 rpm.
All of that energy channels through a close ratio manual six-speed transmission. The tight-shifting stick contains triple-cone synchronizers for first and second gears, double-cone synchronizers for third gear and single carbon synchronizers on fourth through sixth gears to ensure some heavy-duty shifter workouts.
There's no choice for the traction mechanism, as all of the vehicles that Subaru ships to North America arrive with an all-wheel-drive system that's always engaged. Subaru labels the AWD equipment on STI as Symmetrical All-Wheel Drive with Driver Control Center Differential (DCCD) and Vehicle Dynamics Control (VDC). The multi-mode DCCD enables the STI driver to manually manage torque directed to front and rear wheels for performance handling.
It has three performance modes plus six manual differential-locking settings. Further, the STI uses a helical gear-type limited-slip differential in front and a Torsen torque-sensing limited-slip rear differential to garner additional tire traction. Another cool device called Incline Start Assist (ISA) keeps STI's wheels firmly planted on a steep grade.
A super-stiff body structure from Subaru's ring-shaped reinforcement frame contains a four-wheel independent suspension system with inverted-strut front suspension using forged aluminum-alloy lower A-arms and a double-wishbone rear suspension with STI-designed aluminum components. The performance brake system by Brembo sets ventilated discs at all posts with four-piston calipers in front and dual-piston calipers in back. Brakes tie to a sport anti-lock braking system (ABS) with electronic brake-force distribution (EBD) and electronic brake assist (BA) to enhance stability under hard braking maneuvers.
A functional cockpit design positions two bolstered buckets beside a central console housing the shifter stick. The steering wheel is a three-spoke design wrapped in leather with red stitching and switches added for cruise control and audio system. Also, foot pedals get aluminum covers and rubber grips. Subaru sets the MSRP for a 2009 WRX STI at $34,995, or $36,995 with the BBS forged-alloy wheels in silver or gold.