The Ultimate Subaru WRX STI


When it comes to motorsports, the Isle of Man (IOM) punches well above its weight class. Geographically small and sparsely populated, the 221-square-mile plot of earth quietly nestled between Ireland and England is, in some ways, understandably low-key. For two weeks each year, though, a spotlight in the form of one of the world’s most storied motorcycle races illuminates the isle’s rolling hills, narrow streets and towering cliffs.

The Tourist Trophy (TT) race doubles Man’s population, floods the nation with capital and strings together one of the most arduous road courses ever conceived. For over a century, motorcycle riders have risked life and limb howling along a 37.7-mile loop for competitive glory and the viewing pleasure of spectators.
In 2011, Subaru and Isle of Man native Mark Higgins disrupted this two-wheeled ecosystem by sending a lightly modified WRX STI around the course in just under 20 minutes, breaking the 21-year vehicle lap record. Just three years later, the Manxman (local lingo for an Isle of Man inhabitant) and Subaru returned with a new 2015 WRX STI to shed another 41 seconds from the record.
This year, Subaru decided to raise the bar. Placing confidence once again in Higgins, the automaker partnered with UK motorsport engineering group Prodrive and Subaru Tecnica International to develop a racecar tailor-made to the IOM TT circuit.

The standard Subaru WRX STI is a remarkable piece of engineering: 305 hp and 290 lb-ft of torque power all four wheels via a 6-speed manual transmission. The 2.5-liter turbocharged 4-cylinder engine wastes not an ounce of power, thanks to the Subaru front and rear limited-slip differentials and a Driver Controlled Center Differential (DCCD). Combined with Brembo brakes and a sport-tuned suspension, the stock 2016 WRX STI inhales all types of road surfaces.

At the Isle of Man, however, the WRX STI was destined to be pushed beyond its original limits. Enter Prodrive. In mere months, Prodrive transformed a stock WRX STI into a purpose-built racecar that could handle the TT’s 200-plus corners, elevation changes and geographically compromised road surfaces.

. Interior of the 2016 IOM TT Challenge WRX STI.

The differences between a standard WRX STI and the 2016 TT Challenge Car begin under the hood. While the production engine block remains, every other powertrain component has been uniquely formed. Prodrive developed a tailored crankshaft, intercooler, rods, pistons, gaskets, cams and other internals, with a resulting 2.0 liters of displacement. A larger diameter turbocharger from Garrett®was then added to deliver torque between 4,250 and 8,500 rpm. This setup allows Higgins to keep his foot planted for longer without worrying that thrust will unsettle the car midcorner.

****Subaru WRX STI engine block with uniquely formed components****

Mated to the 600-hp motor is Prodrive’s Xtrac 6-speed semi-automatic sequential gearbox. While most drivers prefer a pair of steering wheel-mounted paddle shifters, Higgins requested a single paddle. In addition to the transmission’s 24-millisecond gear changes, the H-pattern can offer more efficient shifting than linear layouts.

Though the IOM car shares the bones of the WRX STI, its suspension geometry has more in common with a WRC rally car. Four-way adjustable dampers, links, struts, sway bars, cross members and other components are designed to soak up the IOM’s punishing roads while providing the stiffness required for cornering stability. Aiding the suspension’s struggle for traction is a hydraulic active center differential and beefier front and rear limited-slip differentials. Rounding out the racecar’s grip-hoarding hardware is a set of 6-piston AP Racing aluminum brake calipers and 355 mm two piece discs.

******6-piston AP Racing aluminum brake calipers and 355 mm discs*****

Driver-controlled actuated rear wing via a wheel-mounted button.

While the thunder of the Challenge Car’s straight-pipe exhaust hints at its modified menace, its inflated bodywork is equally imposing. A stripped-down cabin, lightweight doors and fenders, and other lightweight materials make it 812 pounds lighter than a standard WRX STI. Downforce is amplified thanks to a jutting, wooden front splitter; hydraulic, driver-controlled rear wing; large air inlets on the hood; and air channels along the body. Speaking of that rear wing, Higgins articulates its movement via a steering wheel-mounted button, increasing or decreasing its pitch in fractions of a second. On straights, the wing is lowered to reduce drag, but under hard braking or cornering, raising the spoiler increases traction. Finally, Prodrive installed a high-strength steel FIA-spec safety cage.