Nothing really revolutionary, except for its engine architecture, is to be found in the commercial Impreza GT turbo. Classic McPherson struts front and rear, vented disks (and recently 4 pot fixed brake calipers) at the front while plain disks and floating calipers are used at the rear. The central differential locking device (a viscous coupler) has been "detuned" in order not to interfere with the standard fitted ABS and this slightly affects the car's handling. A stiffer viscous coupler would have been a better choice from that perspective. The turbocharger used in the European model comes from the Japanese manufacturer IHI and is relatively small compared to those used in similar cars (the Toyota GT4 and Lancia Integrale for instance not to speak of the truck sized turbo fitted in the Ford Escort RS Cosworth). This choice favors low end torque and reduces turbo lag but can, sometimes, be cruelly felt at high engine speeds where the "small" compressor wheel's output drops significantly. The torque split set by the central epicyclical differential is 50-50 front-rear and serves well, in all conditions, the judiciously balanced and stiff body of the car.
As you realize the street version of the Impreza, below its cheapo outfit (which get less cheap looking as the years go by), is a car for drivers that want a car providing the thrills with no frills. Japanese manufacturers are the only ones able to still produce that much of a car for such a low price.
The commercial success of the Subaru Impreza turbo is already impressive. No other four wheel drive turbo charged car has been produced and sold in so important numbers. Rumor has it that Subaru is selling more Impreza turbos in Europe than "normal" Impreza versions. The main reasons for this success are the Impreza's price to performance ratio, its racing successes and its reliability. Add the fact that most car related magazines largely overrate its abilities and you get the huge commercial success the car enjoys. The Impreza turbo is, essentially, a hassle free car to be used everyday the whole year round. Under the family sedan outfit however lurks a road hungry speed monster.
Things (and performance) are, of course, quite different in the competition Imprezas. The GroupA Impreza GT Turbo has scored a total of 11 WRC wins while its WRC class brother has scored 19 WRC wins already. Only the Audi Quattro has scored more WRC wins with a total of 21 so it is no wonder the Impreza has captured the attention of so many fans and is almost a cult car by now.
The car's commercial success has lead Subaru to produce many awesome versions of the Impreza turbo most of which are, unfortunately, not available outside Japan. The most impressive Impreza to date is certainly the WRX STI 22-B version. The car was designed by Peter Stevens the designer of the McLaren F1 road going car himself and is arguably one of the most attractive ones on the market today. The 22B, a WRC Impreza look-alike, contains some very elaborate parts in both its suspension, transmission and engine internals (a one piece steel crankshaft for instance). The car's output is only limited by Japanese regulations which set the maximum engine output of any Japanese car to 280 Bhp (which is exactly the WRX's engine theoretical output but rumor has it the real output is closer to 350 Bhp). The chassis, brakes, engine management and cabin equipment are all top-spec and clearly express the car's main purpose: the fastest A to B times possible. The WRX version of the Impreza turbo was engineered by STi (standing for Subaru Tecnica International). This version sports a GroupN spec gear box, stronger front and rear differentials and heavy duty drive shafts. Additionally die-cast suspension parts and custom suspension springs and dampers allow the driver to fully exploit the car's potential (if he/she dares). In the engine department the WRX Impreza adds a steel crankshaft, new pistons, new cylinder heads and a bigger turbo than the standard version. The exhaust is also specific and made, in part, from stainless steel. These engine modifications allow the red line to be pushed to 8,000 rpm! Subaru finally used adequate wheel sizes on the WRX Impreza eliminating one of the major drawbacks of the standard version. The rims are now 17" in diameter.
The result is a four wheel drive, two door saloon that's got the potential to leave the line as fast as a Porsche 911 RS, cracking the 0-100Km/h dash in just 4.9 sec on its way to a 235Km/h top speed. On top of all this version of the Impreza can corner much faster than the standard spec and is at least 1.5 sec faster per Km on open roads.
Unfortunately if you wish to buy one of these beasts and you live outside of Japan you are on your own. The only way to get your hands on one is through a personal import channel, which is still feasible but complex, and the total cost of such a purchase adds up to approximately US$ 50,000.- It's still worth the money though.
Note that the Impreza GT Turbo and the Mitsubishi Lancer Evolutions, as most other "homologation specials", are not street legal in North America mainly because they fail to meet Emission Control Regulations in these areas.
Apparently Japanese manufacturers are the only ones, today, capable of producing such cars. Why is it that Europeans seem not interested (capable) in designing and producing thoroughbreds such as the Subaru Impreza WRX or the Mitsubishi Lancer RS Evolution V is a mystery to me. Having such arguments in any manufacturer's catalog is a powerful marketing tool which can boost the sales of the whole line of cars produced.
Ultimately the Impreza GT turbo has naturally evolved to become a multiple World Rally Champion with three world championship titles already on its account. The car continues to progress as the years go by but changes occur now mostly under the hull. The latest (and greatest) WRC Impreza yet is the P2000 version that appeared for the first time in the 2000 Portuguese rally only to win it, driven by Richard Burns. The main evolutions that took place, as compared to the previous version, are a better under the hood air circulation, refinements in the suspension layout and geometry as well as more elaborate differential control units. The Impreza P2000 WRC also innovates in the exhaust domain with the back-box now holding an integrated catalyst. The exhaust tubing is now made out of the extremely expensive INCONEL alloy like in many other WRC cars. These latest cars are fitted with fly-by-wire throttle control (no cable is used between the gas pedal and the inlet manifold) as well as sequential gearboxes with switch gear knobs fitted on the steering wheel.