Cosworth Impreza STi CS400

What is it?

The fastest, most powerful and most expensive Subaru Impreza that’s ever been offered for sale in the UK: this is the Cosworth Impreza STi CS400.

You’ll have worked out by now that, unlike pretty much every special Impreza that Britain has ever seen, this car has been developed not by Prodrive but by a different, little-known British engineering firm just up the A43, which also has quite an impressive history in motorsport (cough, cough).

See the first drive pics of the Cosworth Impreza STi CS400

Joking apart, this car is actually the first performance special that Cosworth has developed ‘solo’ since the whale-tail 1996 Ford Escort RS that bore the company’s name. The Northampton firm’s bread and butter remains the development and manufacture of high-performance engines for racing, low-volume road cars, defence and the aero industry, but for this project it plunged in with both feet and took responsibility for chassis specification and set-up, drivetrain upgrades and overall development, too.

What it has produced is a Subaru Impreza STi with a significantly upgraded engine and chassis and some pleasingly stealthy styling modifications, which is capable of cracking 62mph in just 3.7sec, and a standing quarter mile in only 12.75sec. As you’ll already know if you’ve been reading our blogs section, the latter figure is less than half a second slower than a 572bhp Audi RS6.

What’s it like?

Almost as good as you’d expect it to be, even looking back with the rosiest of specs at Cosworth’s old fast Fords. The outfit has done a very thorough job of transforming this Impreza into a rapid but useable road car, and has corrected many of the standard Impreza STi’s shortcomings in the process.

We’ll deal with the chassis and running gear first, because that’s the biggest surprise. Cosworth engineers have kept the Impreza’s major chassis mechanicals – struts up front, independent multi-linked arms at the rear – but has specced Eibach springs that allow the car to run 15mm lower on its front axle. They’ve also gone for specially tuned Bilstein dampers all round, and have changed the STi’s chassis bushings, too. They’ve chosen lightweight 18in wheels and Michelin Pilot Sport 3 tyres, as well as 355mm ventilated front brakes and six-piston calipers from stopper specialist AP.

And as a result of all that, the CS400 is an STi that is much more controlled, responsive and precise to drive, and yet it’s also suited to rutted UK tarmac. That drop in ride height has eliminated a lot of the unsettling initial body roll that standard STis suffer with; it’s also made the car’s steering a great deal more accurate and positive, although it’s still quite light.

But it’s this STi’s damping finesse that’s most remarkable. If you’re expecting a trolley-jack ride, you’ll be blown away. The car feels like it’s got suspension travel and damper control to spare 90 per cent of the time, even on really testing backroads, and those new bushings make it surprisingly quiet and smooth over sharper intrusions.

Oddly, the Cosworth Impreza doesn’t quite blow you away where you expect it to: in the engine department. That’s not for want of effort on Cosworth’s part. It has completely stripped Subaru’s aluminium 2.5-litre flat four in the process of making this engine, and fitted new pistons, bearings, con rods, gaskets, head studs, and a completely upgraded turbocharger, intake system and exhaust. Such is the company's devotion to this car’s powerplant, Cosworth has even taken the oil pump to bits to ensure that it’s working efficiently.