Unsurprisingly, the 2.5-litre boxer engine has been the focus of Cosworth’s attention. It receives a modified turbo and remapped ECU, as well as reworked internal components. As a result, the STi CS400 has 395bhp (400PS / 295kW), and 540Nm of torque. Those are significant improvements over the Impreza STi Type UK which, with the 330R pack (currently being offered to UK buyers as a free upgrade until the end of June), produces 325bhp (330PS / 243kW) and 470Nm.
Almost a second is knocked off the 330R’s 0-62mph (100km/h) time, with the STi CS400 achieving the benchmark sprint in just 3.7 seconds. That’s up there with supercars like the Porsche 911 GT2 RS (3.5 seconds) and Audi R8 GT (3.6 seconds), and it makes the Ford Focus RS500 (5.6 seconds) look distinctly pedestrian.
Perhaps importantly - for Subaru at least - is the fact that its STi CS400 is 0.1 seconds quicker to 62mph than the most powerful Mitsubishi Evolution X, the £52,299 FQ-400 with its 403bhp (409PS / 301kW). One area where the STi CS400 is no quicker than either the 330R or FQ-400, however, is top speed - like them, it remains limited to 155mph.
Chassis improvements include new Bilstein shock absorbers and Eibach springs, which give the STi CS400 a wider track and allow it to ride 10mm lower. The brakes are also upgraded, with 355mm AP Racing discs at the front.
Cosmetically, the Cosworth is distinguished by a new front bumper, mesh grilles, privacy glass and a revised rear spoiler, together with new 18” alloys. The interior gets different Recaro front seats and piano black wood for the centre console.
Its price and performance means the STi CS400 can be looked at in one of two ways: Either it’s a performance bargain, costing a third of a ‘proper’ supercar like the 911 GT2 RS, or it’s just a very expensive hot hatch with a price tag almost double that of a standard £28,000 Impreza STi Type UK.
One thing for sure is that the Impreza Cosworth STi CS400 will be rare. Only 75 are to be built, and they’re all going to be right hand drive.
