Part 2
The 2.5-liter horizontally opposed (Boxer) 4-cylinder engine is based on a specially reinforced semi-closed deck engine block with forged aluminum-alloy pistons, forged high-carbon steel connecting rods and sodium-filled exhaust valves. The Subaru Active Valve Control System (AVCS) variable valve timing technology helps provide strong torque characteristics throughout the engine's operating range.
The turbocharger produces 14.5 psi of maximum boost compared to 13.5 in the standard WRX. The large capacity intercooler uses a manually operated water spray feature to enhance intercooler efficiency during high-performance driving.
Symmetrical All-Wheel Drive With Driver Controlled Center Differential (DCCD)
The Impreza WRX STI is equipped with the brand's most performance-directed Symmetrical All-Wheel Drive system featuring Driver Control Center Differential (DCCD). A planetary center differential provides a performance-oriented 35 percent front / 65 percent rear power split. Set in automatic mode, the electronically managed continuously variable transfer clutch can vary the torque distribution ratio as needed to suit driving and road-surface conditions.
Automatic mode provides the best all-around performance for most drivers and circumstances, varying 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 (up to 50/50 maximum) to optimize All-Wheel Drive performance for varying driving conditions. The driver first selects manual mode with a console-mounted button and then turns a thumbwheel on the center console to select from among six levels of center 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.
A helical-type limited-slip front differential and mechanical clutch-type limited-slip rear differential help to optimize power distribution side-to-side, helping to ensure that the inside wheels don't slip during cornering.
Competition-Bred Chassis
A super-stiff Ring Frame Reinforced body structure with a hydroformed front subframe provides the foundation for the high-integrity Impreza platform. Compared to the standard WRX models, the WRX STI is lowered by 0.4-inch to help yield a lower center of gravity. 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 essentially 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 surface contact pattern for increased traction and cornering power.
Aluminum front suspension lower control arms and aluminum rear suspension lateral links reduce unsprung vehicle weight. The standard BBS light-alloy wheels measure 17 x 8-inches and are equipped with 225/45 ZR17 Bridgestone Potenza RE070 directional performance tires.
The quick-ratio steering system yields 2.6 turns lock-to-lock, and the steering rack uses a “cannon mount” for greater rigidity that improves on-center response. A damper valve helps reduce kickback that the increased rigidity might cause.
Brembo Brakes with Super Sport ABS
Subaru equipped 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 measure 12.7 inches in diameter and 1.2-inch thick and utilize 4-piston, fixed-position calipers. The rear discs are 12.3 inches in diameter and 0.8-inch thick and use 2-piston, fixed-position calipers.
A combination of Electronic Brake-force Distribution (EBD) and the 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 MOMO® 3-spoke leather-wrapped steering wheel. Performance design front seats feature substantial side bolsters, integrated head restraints and embroidered “STI” logos. The seats are upholstered in unique perforated blue high-grip Ecsaine® 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 center, flanked by a 160-mph speedometer, DCCD display and fuel and temperature gauges. All three primary gauges feature aluminum trim rings. Red LED indicators and an illuminated “STI” logo in the tachometer reinforce the sporty driving environment. Previewing the vehicle's performance potential, all the gauge needles swing to their maximum positions when the ignition is switched on, and then return to their normal positions.
The standard automatic climate control system integrates cabin air filtration. The standard 140-watt AM/FM premium stereo plays through six speakers and includes a 6-disc in-dash CD changer. An engine immobilizer security system is standard equipment.
New Safety Technology for 2006
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 – first 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 integrate 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.
For additional information about Subaru of America, Inc. and Subaru vehicles, visit the media website at
www.media.subaru.com.
About Subaru of America, Inc.
Subaru of America, Inc. is a wholly owned subsidiary of Fuji Heavy Industries Ltd. of Japan. Headquartered in Cherry Hill, N.J., the company markets and distributes All-Wheel Drive Subaru vehicles, parts and accessories through a network of nearly 600 dealers across the United States. Subaru is the only car company that offers Symmetrical All-Wheel Drive as standard equipment on every vehicle in its product line.