Subaru Impreza STI Cosworth CS400: Only 75 Made

The Subaru Impreza STI Cosworth CS400 stands as a pinnacle of hot hatch evolution, merging Subaru’s renowned rally-bred engineering with Cosworth’s storied Formula 1 tuning prowess. Launched in 2011 as a UK-exclusive limited edition, this model transformed the standard Impreza WRX STI into a 400 horsepower beast capable of humiliating supercars on the drag strip while retaining everyday usability.

Genesis of a High-Performance Collaboration

Subaru’s partnership with Cosworth marked a bold revival of the British tuner’s road car legacy, absent since 1996. Building on the Impreza’s World Rally Championship heritage, the CS400 project aimed to deliver extreme performance through meticulous upgrades. Production capped at just 75 units ensured instant exclusivity, with each car hand-assembled and priced at £49,995 on-the-road.

Available in right-hand drive only for the UK market, buyers chose from Spark Silver, Dark Grey, or San Remo Red exteriors. Subtle styling tweaks—like a revised front bumper, body-colored grille, fog lights, and a discreet rear lip spoiler—distinguished it without garish additions, preserving the Impreza’s understated aggression.

Powertrain Revolution: From 300 to 400 PS

At its core lies a heavily revised 2.5-liter turbocharged EJ257 ‘Boxer’ flat-four engine, Subaru’s signature horizontally opposed design. Cosworth engineers stripped each unit for hand-finishing, installing upgraded pistons, connecting rods, bearings, head gaskets, and a high-pressure oil pump to withstand boosted pressures.

A larger turbocharger, free-flow exhaust, and ECU remap unleashed 400 PS (395 bhp) at 5,750 rpm and 542 Nm (400 lb-ft) of torque—a 33% power surge over the stock STI’s 300 PS. This propelled the CS400 to 62 mph in 3.67 seconds, a quarter-mile in 12.75 seconds at 107 mph, and a limited top speed of 155 mph.

The upgrades prioritized reliability, adhering closely to OEM designs for dealer servicing. Twin overhead camshafts (DOHC) and Active Valve Control System (AVCS) variable timing optimized low-end grunt alongside peak output.

Drivetrain and Transmission Enhancements

Channeling this fury through all four wheels, the CS400 retained Subaru’s full-time symmetrical All-Wheel Drive (AWD) with front and rear limited-slip differentials. A driver-controlled center differential with viscous coupling dynamically adjusted torque splits—defaulting to 50/50 but shifting in milliseconds for optimal grip.

The six-speed manual gearbox gained carbon synchromesh on 3rd-6th gears, a short-throw shifter, and an uprated single-plate clutch with revised pressure plate and disc. Final drive ratios stayed stock to balance acceleration and usability.

• Key Drivetrain Features:
• Active torque vectoring via multi-mode center diff
• Carbon-synchromesh for precise shifts
• Enhanced clutch for 33% power increase
• No changes to gear ratios for tractability

Chassis Dynamics: Precision Tuning for Track and Road

Cosworth overhauled the suspension with Bilstein adjustable dampers and Eibach springs, lowering ride height by 10 mm for sharper handling. Track widened by 12 mm via 18-inch alloys shod in sticky DOT-approved semi-slicks, boosting cornering poise.

Braking received supercar-grade attention: 355 mm ventilated front discs gripped by AP Racing six-piston calipers with bespoke pistons and larger pads. Rear brakes remained potent, ensuring fade-free stops from high speeds.

Interior Refinements and Practicality

Cabin changes were minimal yet purposeful, emphasizing sport over ostentation. Recaro sport seats offered superior bolstering, complemented by piano-black trim, Cosworth badging, and tinted glass. Practicality endured with the hatchback’s versatile cargo space and family-friendly dimensions.

Daily drivability shone through: the AWD system tamed wet roads, while the boxer engine’s low center of gravity enhanced stability. Fuel economy hovered around 25-30 mpg combined, respectable for its output.

Rarity and Collectibility in the Modern Era

With only 75 produced—all sold out pre-launch—the CS400’s scarcity drives collector demand. Examples like chassis #50, registered in January 2012, now fetch premiums as appreciating assets. Its unmolested survival rate remains high, thanks to robust engineering and Subaru’s service network.

Today, it outperforms many contemporaries: faster than a Porsche 911 Carrera S to 62 mph, with AWD grip unmatched by rear-drive rivals. Maintenance focuses on turbo health and clutch wear, but parts commonality with STI models keeps costs reasonable.

Performance Benchmarks and Real-World Testing

Independent tests validated claims: Autocar magazine clocked 0-60 mph in 3.5 seconds, praising its launch control-like traction. On twisty B-roads, the CS400’s balance rivaled mid-engined exotics, with precise steering and minimal body roll.

Quarter-mile prowess—12.75 seconds—put it ahead of Nissan GT-Rs of the era, while top-speed runs hit the limiter effortlessly. Noise levels stayed civilized, with a purposeful turbo whoosh and exhaust burble.

Legacy: Influencing Subaru’s Performance Lineage

The CS400 bridged Subaru’s WRC exit in 2008 and Prodrive split, injecting fresh excitement via Cosworth. It foreshadowed later STI models like the S209, proving the Impreza platform’s tunability. Enthusiasts hail it as the ultimate ‘Blobeye’ evolution.

In gaming culture, it starred in Need for Speed titles, cementing pop status. Its formula—boosted boxer, AWD, manual—defines Subaru’s enduring appeal.

Buying Guide: What to Look For

Prospective owners should verify:

• Full service history from Subaru specialists
• Genuine Cosworth components (engine plaque confirms)
• No accident damage; check chassis rails
• Clutch condition (high-mileage replacements common)
• Turbo boost logs for health

Avoid modified examples; stock CS400s appreciate fastest. Budget £40,000-£60,000 for pristine units as of 2026.

FAQs

This hot hatch redefined expectations, proving affordable engineering could rival exotica. Its blend of raw power, grip, and rarity secures a hallowed spot in automotive history.