Page 1 of 1 Sure to appeal to enthusiasts, a driver's control centre differential (DCCD) becomes standard on the WRX STi. The DCCD is operated via a switch mounted next to the handbrake and allows the driver to manually select the torque distribution front to rear, reverting to automatic mode every time the ignition is turned off. For example, he or she can choose between having a sharper cornering turn-in or more stable straight-line running. However, on the new 2005 Impreza WRX STi, the system is further upgraded by the fitment of a yaw-rate sensor and new front helical limited-slip differential. The new front LSD is quicker-acting than the previous type and improves steering stability when cornering near the limit. It also improves the car's steering behaviour on slippery surfaces with less side-to-side tug. Meanwhile, the yaw rate sensor enhances the balance between straight-line stability and turn-in. The car, of course, continues to employ Subaru's much-admired symmetrical, full-time all-wheel drive system with a rear LSD.
The 2005 Impreza WRX STi also has a completely revised suspension with new geometry including a caster angle raised by 1.5 degrees and a 15 mm wider rear track and 10 mm longer wheelbase. Spring and damper rates have been retuned and the front and rear lateral links are now made from aluminium to reduce unsprung weight. Also changed are the anti-roll bars which are now bigger, further reducing body roll and increasing handling sensitivity. In addition, the suspension mounting points are more rigid including the support arm for the front cross-member and jack-up plate which are now a single unit. Even the front axle hub units and housings have been redesigned to improve the capacity of the wheel bearings, while the rear differential cushion rubber has been uprated to increase handling stability.The Impreza WRX STi's steering has also undergone engineering refinement, making for greater precision and feedback. This is achieved by using a cannon mount-type attachment for the steering gearbox. Meanwhile, a special damper valve has been added to the system which reduces kick-back during hard cornering or when driving on a bumpy road. Other technical changes include the fitment of engine and floorpan underfloor covers to improve the aerodynamics.
Like the rest of the '05 Impreza range, significant changes have been made to the interior to enhance the ambience while retaining the Impreza STi's sporty character. Specific new features for the STi include a new design of gear lever and three-spoke steering wheel. Even the seat trim has come in for re-examination, and while the popular blue suede-effect centre section with red STi logos continues, the black cloth covering the side supports is now of a richer, more grippy material. On opening the bonnet, the engine compartment greets owners with a dramatic mixture of colours and detailing. The intake manifold, for example, is painted in red and the enlarged aluminium intercooler emblazoned with 'STi' lettering. Tuned by Subaru Tecnica International Inc, up to 80 per cent of the STi's all-alloy engine is new compared to the standard Turbocharged 2.0 litre four-cam 'boxer' unit as fitted to the regular Impreza WRX. Engine strength and rigidity are boosted by using semi-closed-deck cylinder blocks, reshaping the piston head, fitting screw-in type connecting rods and using forged pistons and shimless valve lifters. Also aimed at high-rev durability are sodium-filled exhaust valves and hollow intake valves. A larger intercooler and air intake provide better cooling and a special intercooler water spray is fitted, operated by the driver with the water tank fitted in the boot. Also specially fitted to the STi is Subaru's Active Valve Control System - variable valve timing - which ensures maximum engine response over a wide rev-range. Page 1 of 1