For years, the United States seemed doomed to receive only the cast-off leftovers of the foreign world. Nissan kept away the Silvia and the Skyline GT-R, giving us the 240SX. Mazda kept producing the third-generation RX-7 long past the kill date in the U.S. Subaru finally gave in to logical thought at the turn of the 21st century opening up a new age of factory turbo tuning with the Impreza WRX. The only thing was, the Japanese manufacturer continued to keep a little bit something special in reserve just for the Land of the Rising Sun.
Stuffed to the brim with extra words in its name, the Subaru Impreza WRX STi Spec C is the edgy, race-ready, performance demon we wished the U.S.-destined STi had been born with. Where the USDM 2.5L STi is a big-bore hot rod that points and shoots, the Spec C carves with little abandon. With the Spec C, little thought has been given to the ways of emissions-driven engine displacement requirements or to luxury, plush ride quality. The Spec C demands revs and boost to be driven to its fullest, and is the true and rightful contender to Mitsubishi's Lancer Evolution.
With such a pedigree for speed, it comes as no surprise that JDM tuner Auto Produce Boss decided to build this amazing Spec C Time Attack car. Having already built some seriously tuned turbocharged demo cars - a 493hp Supra and a 520hp S15 Silvia - Auto Produce Boss went into the Subaru build fully focused on bringing home some quick lap times at the Tsukuba circuit.
The JDM EJ207 engine is of a semi-closed deck design and fit with better cylinder heads, AVCS variable valve timing technology, and a twin-scroll turbocharger far superior to the motor formerly used in the standard USDM WRX. For this build, the 2.0L powerplant was fitted with a Boss equal-length stainless steel exhaust header and an HKS GT turbocharger, which flows exhaust gases into a Boss downpipe, high-flow catalytic converter, and 90mm titanium exhaust muffler.
The HKS S-Type front-mount intercooler is fed by Boss custom piping while the air flow meter has been changed out in favor of an HKS D-Jetro unit to work in conjunction with the F-Con V Pro engine management system. The engine also features a full JUN Auto Mechanic lineup including cams, cam sprockets, valve springs, connecting rods, crankshaft, and pistons. HKS 1.2mm head gaskets were inserted and SARD 800cc fuel injectors replace the factory units, fed by a Boss fuel pump.
With the Blitz SBC i-D boost controller dialing in 19.9 psi of boost the Spec C makes 443 hp at 5550 rpm and a very strong 503 lb-ft of torque at 4550 rpm. These power figures were obtained using Japanese premium gasoline, which is roughly equivalent to 100-octane fuel.