In the late 1980's, Subaru created the Subaru Tecnica International (STI) division to coordinate development for the FIA World Rally Championship and other motorsports activities. After the company had grown, the division was used to create high-performance consumer versions of the Subaru Impreza WRX, an AWD car with a turbocharged flat-4 engine, leading to the development of the Impreza WRX STi. Subaru has used a race-prepared version of the WRX STI as its rally platform since the model trim's creation.
In 2001, the Impreza line received a complete update. The chassis was stiffened so that it had 120% torsional stiffness increase. The WRX STi gained 17" x 7.5" alloy wheels over the previous 16" x 7" wheels. The 5 speed transmission (reputed to be one of the car's weakpoints) was changed to an STi engineered 6 speed manual transmission. The engine was retained from the Version 6 STi and still retains the semi-closed deck block and is still labeled as the EJ207. However, the turbochargers are IHI models. The interior was updated with a STi logo on the gauge. The STi's gauge also has a red shift light. The STi's and optioned Type RA STi have received Brembo 4 pot front and 2 pot rear brakes while the bare-bones Type RA STi still carried the Subaru 4 pot front and 2 pot rear brakes. Externally, the STis had larger hoodscoops and had foglight covers with STi embossed on them. The DCCD was updated so it can work with anti-lock brakes. During braking, when the ABS is on, the DCCD will set itself to open-mode (no locking).
The version nomenclature was dropped from the name. To distinguish between the years, Japanese and other auto-enthusiasts often refer to the chassis as GDB (the STi had a 'B' where as the regular WRX had an 'A') revision A to F where F is the current (2006) version.
Rev. A (2001): In 2001, the WRX STi received the aforementioned updates. The WRX Type RA STi was produced. The STi wagon was still produced but it's engine only produced 260 PS (191 kW). The STi foglight covers had white STi lettering on them.
The WRX Type RA STi was used for the Group N homologation.
Rev. B (2002): Along with the rest of the Impreza line, the grill and body of the WRX STi was minorly updated by Peter Stevens to give it a more angular look when seen from the side. The foglight covers had pink STi lettering. Not much else besides minor suspension improvements and a small increase in torque output was done.
The WRX Type RA STi was dropped for a new WRX STi Spec C. This model was much lighter than the WRX Type RA as it received lighter glass and body panels. The Spec C's handing was much improved due to an increase in caster (from 3.5 degrees to 5 degrees). This was achieved not by changing the suspension mounting point, but by lenghtening the wheelbase (15 mm). This was done by including different control arms. This increased caster significantly helped the turn-in capabilities of the car. The Spec C also has a steering rack ratio of 13:1. The transmission is supplied with its own oil cooler.
The WRX STi was used for Group N homologation.
The WRX STi wagon had ceased to be produced.
Rev. C (2003): Not much was changed.
The WRX STi was used for Group N homologation.
Rev. D (2004): The WRX STi received the same Peter Stevens-designed facelift that rest of the Imprezas received. The WRX STi is now capable of being ordered with DCCD.
The WRX STi Spec C Type RA was released. It sported a carbon-fiber wing and a carbon fiber lip. It also had a new set of BBS wheels as well as a newly tuned engine.
The WRX STi V-limited was released. It sports 4-way dampers tuned by Subaru World Rally Team's Group N driver Toshi Arai.
The WRX STi was used for Group N homologation.
Rev. E (2005): The WRX STi receives the same increase in wheelbase as the Spec C. All STis received additional rear fender flaring in order to allow an increase in wheel size. The wheel size went from 17" x 7.5" to 17" x 8". In accordance with the increased wheel width, steering lock-to-lock turns have been reduced. Wheel hub strength was improved. The P.C.D. was changed from 5 x 100 to 5 x 114.3.
The DCCD mechanism is improved with the addition of a yaw rate sensor that helps the AWD's computer determine torque distribution to the wheels.
The WRX STi Spec C WR-limited was used for Group N homologation.
Rev. F (2006): The WRX STi continues on relatively the same. The Impreza line's looks have been changed by Andreas Zapatinas.
The WRX STi Spec C's receives the Arai tuned dampers and a 21-mm swaybar. The rear suspension is changed from rubber bushings to pillowball bushings. The strut tower was further stiffened for improved handling and stability. The strut towers were reinforced for better handling and better ride characteristics. The engine mounts were changed from metal to liquid-filled plastic mounts to reduce vibrations into the car's cabin.
The DCCD is updated with the use of a torque-sensing mechanism inside the DCCD. The torque split is changed to 41/59.
The WRX STi Spec C was used for Group N homologation.
Japanese-spec Special Variants
S202: This car was an S-series Impreza based on the Spec C. All of the suspension and powertrain parts included STi parts from the STi part catalogue. The interior included special edition black seats with red STi logo stitching. A smaller, lightweight AC compressor was fitted to save weight. The brake rotors were gas slotted. The rims were STi labeled Ray's Volks rims.
S203: This limited edition Subaru was an S-series Impreza based on the WRX STi. Again it is basically a car with all the STi parts available. It was shod with custom made 18 inch BBS rims with Pirellis. The crankshaft is balanced by hand.
S204: The new S204 was released at the end of 2005. It is based on the WRX STi and similar to the S203. It does away with the roof spoiler and has a different grill from the rest of the Impreza line.
Asia, Oceania and European-spec
In 2001, most of Asia, Oceania and Europe received the new STi. The engine was detuned to meet emission standards. Instead of the stated 280ps, the engines produced 265 PS (195 kW).
In 2006, the engine was changed to the EJ25 and produces 280 PS (206 kW). The STis finally received the DCCD that US models had from the beginning and the extra wheelbase increase like the Japanese-spec WRX STi Spec C.
In 2004, Subaru of America announced it will sell the WRX STi. Subaru Tecnica International's president said in an interview that he wishes to best the Mitsubishi Lancer Evolution in the US. Thus, the each iteration of the US-spec WRX STi was essentially the same as the respective J-spec STi Spec C (the highest performing STi version barring special variants). All the part numbers match up, including the part-numbers for the glass windows and dampeners. However, instead of the EJ207, the USA receives the first EJ257, a 2.5 liter version of the EJ207. Also, unlike the EJ207, it features hypereutectic cast pistons as opposed to the forged pistons in the EJ207. The steering rack is the standard STi's 15.2:1 instead of the Spec C's 13:1
Many people surmise the reason why the US-spec WRX STi does not handle as well as a Spec C is because the EJ257's extra weight and the slower steering rack hampers the feel and balance of the car.
The MY2006 STi weighs approximately 3350 lb.
GC chassis comparison to the GD chassis
Subaru claims that the GD chassis is 148 percent and 82 percent stiffer in torsional and beam rigidity, respectively, than the GC chassis. Due to the increase in stiffness, the car has much better stability in corners and is easier to control at the limit. The GC chassis is so weak compared to today's cars that engineers called the body a "Watermelon frame", referring to how a watermelon shatters on impact.
In terms of safety, the IGD chassis scored much higher than the GC chassis and earned a "Good" rating (highest mark) from the IIHS's offset crash test. 4 stars front driver, 5 star front passenger and 4 star side safety ratings from the NHTSA. In a magazine article from the Dec. 2005 Firehouse magazine (a periodical written and made for firefighters), Ron Moore writes how it is well-known that the Impreza chassis has great protection in its B-pillars. This side structure has 8 layers of high-strength, high-tension steel including a round steel bar running through the middle. The author notes how drivers simply walk away from horrific side-impact accidents.
One of the biggest complaints with the GD chassis is that it gains nearly 200 kg in weight over the GC chassis. Much of this weight came in the form of chassis stiffening as the car was made to meet every countries' crash standards. The weight also hampers the cars maneuverability, transistions and turn-in capabilities. The GC Imprezas were notable for being very lightweight despite having AWD, the WRX Type STi Version VI, at 1260 kg, was lighter than the concurrent Mazda RX-7 type RZ (1270 kg) and Honda NSX type S Zero (1270 kg). In this fashion, the GC chassis has a better advantage.
The author mentioned above also notes that the Jaws of Life need to cut the Subaru's B-pillars at certain points in order to cut through the car frame. This information was not as well-spread before, so there have been many incidences where firefighters could not cut the B-pillars due to their structural integrity. To some people, this might be a concern if the driver or passengers need to be cut out of the vehicle quickly.
The STI was originally sold only in Japan. It was later made officially available in Oceania (Australia had it in 1999 with the STi Version V). In 2001, Europe received the STi with the change of the chassis. After seeing the Impreza WRX sell at much better levels than expected, Subaru began selling the STI in North America in 2004.