The WRX STI S209 encompasses upgrades in power, handling, aerodynamics and driver engagement. Final assembly takes place in Kiryu, Japan, where it receives engine modifications and bodywork alterations that in total require it to be homologated for the U.S. by STI. The S209 is considered the first “STI-built” Subaru sold in the United States. the previous S-line STIs, the 2000 S201 through the 2018 S208, were only available in the Japanese domestic market.
The bulging fenders accommodate wider front/rear tracks (+ 0.6 in front/rear) and 265/35 Dunlop SP Sport Maxx GT600A performance tires fitted to lightweight 19 x 9-inch forged BBS alloy wheels. The all-new tires, developed exclusively for the S209 by Dunlop, are a significant contributor to the car’s maximum lateral grip of over 1.0 g. Vents on the front fenders provide additional engine cooling, while vents on the rear fenders rectify air turbulence to reduce drag. Brembo brakes, with cross-drilled steel rotors and 6-piston monoblock front calipers and 2-piston monoblock rear calipers, provide greater braking capability thanks in part to upgraded high-friction pads that deliver improved fade-resistance.
The S209 has specially developed Bilstein dampers, stiffened coil springs, a 20mm rear stabilizer bar and pillow-type bushings for the front/rear lateral links. The S209 incorporates reinforcements to the front crossmember and rear subframes and, like the Nürburgring race car, a flexible front-strut tower bar and flexible front/rear draw stiffeners. The flexible tower bar, unlike a conventional rigid bar, is split and joined with a pillow ball joint in the center to be longitudinally mobile while helping laterally stiffen the body of the car. The result is optimum tire grip during lateral moments combined with compliant ride during longitudinal moments. Other Nürburgring race car tech that trickled down to the S209 include front, rear and side under spoilers; front bumper canards; and carbon-fiber roof panel and rear wing.
The S209 is only available with a close-ratio 6-speed manual transmission that routes power to a full-time Subaru Symmetrical All-Wheel Drive system with front/rear limited-slip differentials, a Driver Controlled Center Differential (DCCD), Active Torque Vectoring and Multi-Mode Vehicle Dynamics Control. A recalibrated SI-Drive system offers three modes: Intelligent (I) for improved fuel economy and smoother power control; Sport (S) for optimized power balance between response and control; and Sport Sharp (S#) for achieving the best acceleration times. STI engineers recommend Sport over Sport Sharp for circuit driving, as the less aggressive throttle map allows for greater driver control.
To feed more air to the EJ25, the S209 uses a high-flow intake system featuring a new intake duct, induction box with conical air filter, silicone turbo inlet duct and, a nod from the 2004-07 WRX STI, an intercooler water spray system that lowers intercooler temperature via manually operated steering-wheel paddles. More air demands more fuel, so the S209 receives a new high-flow fuel pump, larger fuel injectors and an STI-tuned engine control module. High-performance mufflers deliver 17-percent less airflow resistance while larger hand-polished stainless-steel exhaust tips – 101mm in diameter – deliver aggressive appearance and acoustics.