The Cosworth incarnation of the revered STI develops a mammoth 295kW and 540Nm from the highly-modified 2.5-litre boxer engine, with acceleration to match a Lamborghini Gallardo LP 560-4.
The sprint from zero to 100km/h takes just 3.7 seconds which is way ahead of its traditional rivals, the Mitsubishi Evolution and Ford Focus RS, with an electronically limited top speed of 250km/h.
The upgraded engine has been blessed by the full Cosworth parts catalogue, including high-performance pistons, high-strength steel conrods, Cosworth-spec engine bearings, a redesigned head gasket and a high-pressure oil pump.
A bigger turbocharger with a new compressor design and wastegate actuator has also been bolted on with a custom exhaust fitted to match.
The suspension has been overhauled using parts from Bilstein and Eibach, with the car sitting 10mm lower than standard.
An AP Racing brake package sits behind new 18-inch wheels which widen the CS400's track by 12mm over the standard STI.
The exterior upgrade is finished with a blacked-out front bumper, mesh grille and rear spoiler, plus a few Cosworth badges thrown in for good measure.
Just 75 examples of the Cosworth Subaru Impreza STI CS400 will be available, exclusively to the UK market.
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