Press Release
3. Powertrain
[2.0-litre turbo Boxer engine]
An electronically controlled throttle enables finely adjusted control of the 2.0-litre turbo Boxer engine and ensures acceleration that is linearly responsive to pedal movement. The Dual Active Valve Control System (Dual AVCS) hydraulically controls timing in both the intake and exhaust valves, which helps improve low-end torque while providing a strong power boost at high rotations. Dual AVCS also increases combustion efficiency, thereby reducing exhaust emissions. Changes made in the intake and exhaust ports promote smoother air in- and outflow, contribute to enhancing power output, and improve combustion efficiency, which reduces emissions and improves fuel mileage. In addition, changes in the shape of the turbocharger compressor have increased the efficiency of the air intake and enabled more responsive and smoother acceleration.
Also, the layout of the exhaust pipes greatly facilitate overall air outflow by canceling interference and
increasing airflow between the exhaust port and the turbo charger to deliver optimal torque and engine response at various speeds. A tumble generated valve (TGV) has been installed in the intake manifold, boosting combustion efficiency by controlling the intake flow. It improves efficiency particularly at the time of engine ignition. Also adopted is a secondary air system that forces air into the exhaust port to burn out any gasoline remaining in it. The system helps eliminate harmful substances when the powertrain is still cool, and it promotes early activation of a catalytic converter.
The muffler is placed horizontally, which lowers resistance in the exhaust flow, results in improved noise cancellation, and contributes to smooth power output.
[Transmission]
A 6-speed manual transmission, Subaru's own development, has been further perfected for faster, more accurate and responsive shifts. Friction is substantially reduced through the adoption of a triple-cone synchromesh in the first gear and design changes in the shift sleeves.
4. Drivetrain
The front differential gear adopts a torque-sensitive LSD (limited slip differential) that excels in response to input torque; the rear differential employs the Torsen LSD that supports distribution of torque. The SI (SUBARU Intelligent)-Drive system offers three different modes of driving for the driver to enjoy: Intelligent; Sport; and Sport Sharp. For example, when a driver continues to heavily depress the accelerator pedal in the Intelligent mode, engine output is automatically boosted to the level of maximum torque. The multi-mode Driver's Control Center Differential (DCCD) enables the driver to choose from different modes of control for the center differential. This feature allows the driver to enjoy handling and maneuvering as he desires, and it provides high levels of vehicle straight-line stability unique to the AWD configuration.
The multi-mode Vehicle Dynamics Control (VDC) also provides three different modes that the driver can choose from to experience a wider range of driving enjoyment, while always maintaining the safety features of VDC.
[Multi-mode DCCD]
AUTO mode: The standard mode automatically controls the differentials under all kinds of driving
conditions. AUTO [+] mode: This mode is suited for driving on slippery or icy roads, which requires higher levels of road traction, achieved by elevating differential control. AUTO [-] mode: This mode enables agile driving whereby the vehicle responds swiftly to steering by the driver. MANUAL mode: This mode allows the driver to control the center differential manually.
[Multi-mode VDC]
NORMAL mode: The standard mode controls ABS, TCS and VDC. TRACTION mode: Adjusting both TCS and VDC, this mode extends the time period until the VDC kicks in. This mode is suited for sporty driving as it does not control torque-lowering in the engine.OFF mode: This mode only controls ABS. It is used in emergencies like getting the vehicle out of deep snow or mud.
*Though the multi-mode VDC is the vehicle stability control device that offers a superior function, it is a driving assist system.
5. Chassis
The WRX STI boasts a state-of-the-art chassis design that reflects the Subaru DC3. Equipped with a strut-type front suspension and the newly designed double-wishbone rear suspension, and combined with its widened track, this model achieves outstanding cornering stability. Optimized suspension geometry settings with adjusted camber angles have made substantial improvements in road-hugging traction and riding comfort. Aluminum cast lower arms and a stabilizer bar in the front suspension help raise torsional and rolling rigidity, providing accurate response in steering. In the rear suspension, suspension links are attached to the body through the sub-frame, which enhances riding comfort and further lowers noise levels. The Boxer engine is mounted lower on the chassis, further advancing vehicle stability already ensured by its low center of gravity: 22 mm lower at the front end of the engine, compared to the previous model.
The Brembo-made ventilated disk brake system employs an ultra-low expansion brake hose and tie rods for the brake booster. The brake system, coupled with the SuperSports ABS (antilock brake system) with EBD (electronic brake distribution), processes information fed from the G sensor, steering angle sensor, yaw rate sensor, and pressure sensorto deliver steady braking and control. It also works with the DCCD to ensure accurate braking on all four wheels independently, while minimizing deviations from the driver's intended path. Bridgestone RE050A (245/40R18) tires are standard. The hill-start assist function maintains the braking function one second after the brake pedal is released in case of starting a car on a hilly road.
6. Body construction
The WRX STI uses an advanced form of Subaru's legendary and proprietary Ring-Shaped Reinforcement Frame Body Structure, reinforcing each pillar with frames that circle around the body in a ring shape. Reinforcements are now provided to connect firmly between the lower part of the front pillar and upper frames, increasing the strength of the strut attachment onto the body frame. Reinforcements are also added to the upper part of the opening of the rear gate. Through streamlined body construction and the extensive use of high-tensile steel, including 590 MPalevel steel for major body frames, the new model has achieved both high body rigidity and a weight reduction of 11 kg.
