As Cosworth’s forte lies with engines, it’s not too surprising to read that the majority of CS400’s changes rest within the engine compartment. The CS400 retains the STI’s turbocharged 2.5-liter boxer-four-cylinder engine, but it’s received some serious surgery. Cosworth installs new high-performance pistons, high-strength steel connecting rods, and Cosworth-designed engine bearings. A new Cosworth-designed head gasket is also added, along with a high-pressure oil pump, and a revised turbocharger compressor and wastegate.
Cosworth hasn’t disclosed the boost pressures used, but the revisions -- along with a new exhaust system and revised ECU -- are enough to get the turbocharged engine pumping out 395 horsepower and 398 pound-feet of torque. That’s roughly 90 ponies and 103 pound-feet more than a U.S.-spec 2011 WRX STI.
We’d celebrate the car simply for the extra power, but Cosworth didn’t stop there. Engineers at the tuning firm partnered with Bilstein and Eibach to revamp the WRX’s chassis tuning to incorporate new coil springs that drop the ride height by a half-inch. Fourteen-inch AP Racing brake discs were added all around, a significant improvement over the 13- and 12.6-inch front and rear discs used on the 2011 STI.
Cosmetic tweaks are subtle, but they do help differentiate the CS400 from a standard WRX STI. Cossie-tuned Imprezas receive a new front fascia with foglamps, a mesh grille insert, and a unique rear spoiler. Larger 18-inch wheels not only help dress up the car’s appearance, but also increase the STI’s track by a half-inch. Buyers have little say in the exterior décor, but can choose between three paint colors (red, silver, and dark grey). Inside, all cars receive Recaro racing seats in lieu of the stock front buckets.
Only 75 of these incredible machines will be produced, and as we suspected, none will (legally) make their way to North America. The entire production run will consist of right-hand-drive models and will be sold in the United Kingdom. The CS400 will cost a whopping £22,505 more than the base WRX STI, bringing the total to £49,995.
