For 2015 Subaru Rally Team USA has debuted the rallycross version of the new 2015 Subaru WRX STI for team drivers Sverre Isachsen and Bucky Lasek.
The team’s technical partner, Vermont SportsCar, first begins with a stock Subaru WRX STI right off the showroom floor. The car’s interior is then stripped bare, and the shell lightened then fully-seam welded for added strength. A multipoint roll cage, manufactured from T45 steel, is then welded into place. Fully prepared, the dry weight of the car is around 2,600 lbs., which is approximately 600 lbs. lighter than a stock STI. Global RallyCross Championship (GRC) regulations require a minimum weight with driver of 2,866 lbs., and ballast is added to meet this minimum.
Major differences from the stock STI include the addition of a competition fuel cell, which keeps race fuel contained within a flexible Kevlar bag tank, and a lightweight carbon/Kevlar RECARO SPA ProRacer competition seat with HANS (Head and Neck Restraint System). Other interior additions include a custom STI dashboard, carbon fiber door panels and an onboard fire suppression system.
One of the biggest differences between the rallycross and stage rally specification cars is the relocation of the radiator to the rear of the car. This is done to protect the radiator from flying debris and impacts typically found in wheel-to-wheel rallycross. Cooling air for the radiator enters through custom carbon fiber ducts on the rear doors of the car and exits the rear of the car.
Under the hood sits a 2.0-liter, 4-cylinder, turbocharged and intercooled BOXER engine. Similar to the stage rally car, the rallycross cars feature launch control, a turbo anti-lag system and a hydraulic handbrake. Another major difference between the rallycross and stage rally cars is horsepower. The Global RallyCross Championship requires a 45 mm restrictor on the turbo whereas Rally America (stage rally) requires a much smaller 33 mm restrictor. The restrictor size difference accounts for an increase of well over 200 hp! The rallycross cars produce in excess of 580 hp and an impressive 660 lb-ft of torque.
A Sadev 6-speed, close-ratio dog-engagement gearbox is used, which allows the team drivers to shift without depressing the clutch. The exterior of the car features a custom wide-body kit developed by Vermont SportsCar that uses carbon fiber, carbon-kevlar and other durable composites. The vertically slotted rear wing is made of carbon fiber and optimized to provide maximum downforce, even when sliding sideways.