Subaru Cosworth Impreza STI CS400: 75-Unit 400HP Collector Icon

The Subaru Cosworth Impreza STI CS400 stands as a monumental achievement in automotive engineering, fusing Subaru’s rally heritage with Cosworth’s legendary tuning expertise. Released in 2010, this ultra-exclusive model pushed the boundaries of road-legal performance, delivering 400 horsepower from its turbocharged flat-four engine. Limited to just 75 units for the UK market, it represented the most extreme iteration of the Impreza lineup, blending raw power, precision handling, and aggressive styling into a package that thrilled enthusiasts and set lap records.

Genesis of a Limited-Edition Legend

The CS400 emerged from a bold collaboration between Subaru UK and Cosworth, the renowned British engineering firm famous for powering Formula 1 cars and iconic rally machines. Building on the standard Impreza WRX STI (GR chassis), Cosworth transformed select donor vehicles into track-focused predators. Subaru supplied approximately 75 right-hand-drive Impreza STIs, which Cosworth stripped down, rebuilt with high-performance components, and refined for ultimate speed. This project marked Cosworth’s return to road car production after a hiatus since the 1990s Ford Escort Cosworth, reigniting their legacy in turbocharged supremacy.

Priced at £49,995—nearly double the standard STI’s cost—the CS400 targeted purists seeking unparalleled performance. Each car featured unique badging denoting its production number, emphasizing its rarity. Production wrapped up swiftly, with deliveries starting in July 2010, making these vehicles collector’s items today. Their matte dark paint, subtle aerodynamic tweaks, and aggressive stance set them apart visually, while under the skin lay a symphony of enhancements designed to dominate circuits and streets alike.

Powertrain Mastery: 400 Horses from a Flat-Four Heart

At the core of the CS400’s ferocity is its 2.5-liter turbocharged EJ25 flat-four engine, extensively re-engineered by Cosworth. Standard STI output of around 300 horsepower was obliterated, with new forged pistons, reinforced conrods, upgraded bearings, a reinforced head gasket, high-flow oil pump, and a massive turbocharger boosting power to 400 PS (394 bhp) at 5,750 rpm. Torque surged to 515 Nm (380 lb-ft) at 3,950 rpm, delivered through a close-ratio six-speed manual gearbox and Subaru’s renowned symmetrical all-wheel-drive system.

These upgrades weren’t mere bolt-ons; Cosworth recalibrated the ECU, installed a free-flowing exhaust, and optimized the intercooler for sustained high-boost performance. The result? A 0-60 mph sprint in a claimed 3.7 seconds and a top speed electronically limited to 155 mph (250 kph). Real-world tests confirmed its brutality: 0-100 mph in 15.9 seconds, with quarter-mile times in the low 11-second range. This powerplant echoed the WRC rally cars that made Subaru icons, but tuned for road use with refined manners.

This table highlights the CS400’s edge, where every gram and Newton counted toward supremacy.

Chassis and Suspension: Engineered for Corner-Carving Precision

Cosworth didn’t stop at the engine; the CS400’s chassis received rally-inspired upgrades to harness its power. Stiffer suspension bushings, adjustable dampers, and lowered ride height improved body control, while wider track and recalibrated anti-roll bars sharpened turn-in. The steering rack was quickened for razor-sharp response, and massive Brembo brakes—380mm front discs with six-piston calipers—provided fade-free stopping power. Lightweight 18-inch matte-black alloys shod with Bridgestone Potenza RE050A tires (245/40 front, 255/40 rear) ensured grip levels that bordered on the supernatural.

Drive modes allowed tailoring: drivers could switch between comfort for daily use and full track aggression, adjusting traction and stability parameters. This setup transformed the Impreza’s playful handling into a scalpel-like instrument, capable of shattering lap times at circuits like Bedford Autodrome, where it outpaced rivals in Auto Express tests.

Design and Aerodynamics: Stealthy Aggression

Visually, the CS400 exuded menace with its matte Arctic Gray or Phantom Black paint, a restyled front bumper with larger air intakes, and a massive rear wing channeling WRC aesthetics. Subtle vents and diffusers optimized airflow, reducing lift and enhancing high-speed stability. Inside, Recaro bucket seats in Alcantara and leather, blue-stitched accents, and Cosworth plaques created a cockpit fit for a rally god. Carbon-fiber elements trimmed weight, while the digital dash displayed boost, G-forces, and lap timers for track days.

• Exterior Highlights: Matte finish, wider arches, quad exhausts
• Interior Upgrades: Race seats, Momo steering wheel, titanium shift knob
• Aero Features: Adjustable rear wing, front splitter, side skirts

Track Performance and Real-World Dynamics

On track, the CS400 lived up to its billing as “the fastest, most hardcore Impreza ever.” Videos from Auto Express captured it demolishing lap records, its turbo howl and AWD launch propelling it through corners with four-wheel precision. Reviewers praised its balance: neutral mid-corner attitude, explosive exits, and brakes that scrubbed speed without drama. Yet, it retained road usability—compliant enough for B-roads, with adjustable settings mitigating its 1,505 kg mass.

Owners echoed this: one mechanical review noted its rarity (one of 75) and rally-car fidelity, with rebuilt internals ensuring longevity. Drawbacks? Thirsty fuel economy (mid-teens mpg) and a firm ride, but these were badges of honor for performance purists.

Legacy and Collectibility in 2026

Over a decade later, the CS400’s value has soared. With low mileage examples fetching premiums, its status as the last great analog Subaru performance car endures. No successors matched its handmade intensity amid electrification trends. Enthusiasts cherish it as a bridge between WRC dominance and modern hot hatches, its 400hp flat-four a dying breed.

In collector circles, pristine units command six figures, their Prodrive-Cosworth pedigree ensuring appreciation. Maintenance requires specialists, but Subaru’s robust base keeps running costs reasonable compared to exotics.

CS400 vs. Rivals: A Performance Showdown

The CS400 held its own against Evo and Focus specials, its AWD system providing consistent traction.

Frequently Asked Questions (FAQs)

How many CS400s were made?

Exactly 75 units, all right-hand drive for the UK market.

What’s the top speed of the Subaru Cosworth Impreza CS400?

Electronically limited to 155 mph (250 kph).

Is the CS400 street-legal?

Yes, fully road-legal with track-focused tuning.

What engine mods define the CS400?

Cosworth pistons, conrods, turbo, oil pump, and ECU remap for 400 PS.

Current market value in 2026?

Low-mileage examples exceed £100,000 due to rarity.

Buying and Owning a CS400 Today

Prospective buyers should inspect for turbo wear, suspension bushings, and clutch condition. Specialist tuners like Prodrive offer servicing. Its all-weather AWD shines in the UK, but tire costs are high. For track days, it’s unbeatable value among JDM legends.