Meet the Subaru Impreza STI CS400, a.k.a the Impreza Cosworth. In short, the 2,5-litre engine has been tuned to 295 kW – a massive 74 kW gain over the regular STI – allowing the 0 – 100 km/h time to drop by 1.5 seconds to a claimed 3.7 seconds. Only 75 examples will be built and that’s about all that’s been made public so far.

So how did this exclusive STI come about? Well, Subaru, anxious to restore some much-needed sporting credibility to the Impreza, approached Cosworth about a possible collaboration 15 months ago. This may seem an unusual partnership given Subaru’s historic ties with Prodrive in the UK, but Cosworth already had experience with the turbocharged flat-four through its US tuning division. Based in California, it has been modifying boxer engines for the West Coast tuning scene for several years – often extracting between 440 and 600 kW.

So five Imprezas were delivered to Cosworth’s unassuming headquarters in Northampton for work to be carried out. Although you might think of Cosworth as a company known exclusively for engine tuning, the company’s talents in fact run deeper. The firm took responsibility for the entire development process, the result of which is a car with new Eibach spring and Bilstein damper units, a 10 mm front suspension drop, a 10 mm wider rear track and AP Racing front brakes with six-pot calipers gripping 355 mm discs with a unique groove pattern.

The aim wasn’t to create a trackday special, but a fast road car, one that retains the driveability of the standard STI but, in the words of Kenyon Neads, Subaru UK’s marketing director, “takes it to the next level”. Neads says “When you do drive it, I think you’ll find that the dynamics, the composure, stability and power delivery has created a very different and better car.”

The understated appearance of the CS400 backs up his assertions. The rear wing is unaltered, the wheels are still ‘only’ 18-inches, and the colour choices are limited to silver, red and the dark grey pictured here. Look closer and you might spot the new mesh grille, badges and the darkened glass – besides the Cosworth branding, each car will wear an engine signature and a numbered plaque on the door sill.

Inside, the seats have been re-trimmed and feature fatter bolstering, while the liberal application of piano-black inserts has helped lift the ambiance a fraction – though it still doesn’t look or feel like it costs almost double that of a standard STI, which it does.

However, Neads says “This is the ultimate manifestation of where we think we can take the STI, but this partnership with Cosworth is ongoing”. In other words the two firms have invested heavily in this car – too heavily for them to call it quits after just 75 units. So expect to see another model, probably with around 260 kW in future.

One final thought about the CS400. The reputations of both firms are on the line: for Subaru this is a chance to prove it hasn’t lost its touch, that the hatchback Impreza platform can play host to a drivers’ car every bit as good as the old saloons. For Cosworth this is the first time its name has appeared on a road car since the demise of the Escort Cosworth in 1996. Both are determined to get it right. Let’s hope the chemistry has worked.

Adapted from Evo

Great news for Scooby fans is that the company has launched an updated Impreza WRX STI – in both sedan and hatchback body styles!

Aside from the obvious addition of a wide-body kit, previewed on the WRX model earlier in the week, with the return of the massive rear wing, the other big news for 2011 comes in the form of a thoroughly reworked suspension. Subaru says the 2011 STI received chassis tuning to accommodate new aluminum front lower L-arms that reduce unsprung weight. Ride height has also been lowered and new pillow-ball bushings were installed up front, with stiffer bushings out back for the double-wishbone suspension-supporting rear subframe.

There are also thicker front and rear stabilizer bars – up 1 mm front and rear – which help to increase spring rates by 15.6 percent in the front, and a substantial 53 percent in the rear. The new 18-inch aluminum wheels weigh an impressive 7.9 kg’s less than the previous standard wheels. There are also optional 18×8.5-inch BBS forged aluminum wheels that reduce unsprung weight even further by losing another 2 kg’s each, while sporting a silver high-luster paint for 2011.

To help stop the 2011 STI while pushing its new found suspension to the limits, is the Brambo Performance Brake System – exclusive to the STI model. The Brembo package calls on ventilated four-wheel Super Sport ABS disc brakes with electronic brake-force distribution, or EBD. The combination of these systems allows for brakes forces to be controlled individually at each wheel, optimizing braking and reducing understeer.

The potent 221 kW intercooled and turbocharged 2,5-litre Boxer engine remains under the bonnet for 2011, along with a six-speed manual transmission.