Near-freezing temperatures and unsuitable driving conditions drove 79 of Japan's top manufacturers and their respective drivers to the ragged edge at the 16th annual 2005 Tsukuba Super Battle.
Redesigned in the early 1970s, Tsukuba Circuit (TC) was recognized as one of the shortest (distance), yet most uniquely designed courses throughout the land of the rising sun. A technically challenging course consisting of tight radius S-turns and banking corners, the 1.287 mile TC course, located in the Ibaragi prefecture of Japan, became the stomping grounds for many privateers and works manufacturer's looking to push their cars to their maximum potential.
On December 8th 2005, teams trailered their street tuned vehicles from all areas of Japan with high hopes and great expectations of breaking the elusive course record, currently held by the HKS TRB-02 Lancer Evolution at a blistering 54.739 seconds. Among the scores of competitors was the joint ventured team of Tomei Power and Prova Racing, ready to wage war among its adversaries with a fully prepared 2004 Subaru, entitled the Arise Impreza. Built specifically to compete as a top contender within the Tsukuba Time Attack, the Arise Impreza was fabricated from the ground up within the course of two years. While the bulk of the vehicle buildup was slated by Prova of Japan, the engine buildup was specifically handled by Tomei Power and their renowned engineers-a deadly one-two combination that's a force to be reckoned with.
Renowned engine tuners and performance specialists within the Nissan market, Tomei Power was approached by Prova Racing to build their very first project EJ20 power plant. New to the boxer world, the engineers envisioned an engine worthy of the Tomei Power name. With all the necessary parts in hand, Tomei tore apart the EJ20 power plant and proceeded to work around the clock, dyno testing and developing products for their future time attack vehicle. After months of careful consideration, the Tomei engineers developed a winning formula for their Time Attack power plant. Using a Tomei forged 2.2 liter crankshaft the factory displacement was increased from its original two-liter spec. Connected to a set of Tomei forged rods and 92.5mm pistons, the larger displacement offered improved turbo response with minimal lag and maximum engine revability-which proved crucial when battling on the track. Tomei Power, world renowned for their custom headwork, spent much of their R&D on the EJ20's cylinder heads. Both heads were hand ported and outfitted with a set of custom Tomei valve springs. Using the existing factory sodium filled valves; a Tomei 270 degree camshaft with 10.8 degree lift was installed. Strengthening the notoriously weak head gasket of the EJ20 motors, Tomei metal head gaskets and custom Tomei head studs solidify both halves of the motor. Crucial to the success of the engine, the engineers installed a larger ARC oil pan and oversized ARC oil cooler-but before the pan was installed, a Tomei SPL baffle and strainer was bolted down to minimize windage and unwanted sloshing of the Wako's sponsored oil on the new 2.2-liter crankshaft.
The IHI RX6 TCW76 might seem rather large for the average Impreza owner, but for the Tomei/Prova team, this turbo is the perfect combination for the Tsukuba circuit as 1.5 bars of boost pressure pumps cold air though an ARC front mount intercooler kit. With the removal of the factory top-mount intercooler system, Prova used the factory hood scoop to their advantage, producing a trick dry-carbon filtration system as the turbo receives abundant amounts of air when blasting down the tarmac. Is that an exhaust pipe exiting out the front bumper you ask? Try again folks. Custom fabricated and built by Prova, the exhaust manifold with external wastegate dump was designed to exit excess gases out the passenger side front bumper. Perhaps the most intriguing unit on the boxer engine is the prototype intake manifold with built-in velocity stacks. "Months of testing and designing were put forth into building this custom intake manifold," stated Tomei Power marketing manager Eiji Mihara. Final results on the engine dyno indicated an improvement of overall air flow characteristics over the factory manifold. Custom 80mm charge pipes with Wiggins clamps complete the engine buildup. With the final piece assembled on the engine, the EJ powerplant was carted off to Prova, where the next stage of the buildup process was to begin.
Weight has long since been nemesis among the Subaru camp. In hopes of scaling back and trimming unwanted fat, the GDB undertook a body conversion that took shape in ultra lightweight dry carbon. The Impreza's body was outfitted with an array of dry carbon components including the front and rear bumpers, hood, rear wing, and front splitter. Prova, a company made famous for building and fabricating Super Taikyu (N1 enduro) race vehicles in Japan, not only designs their own body kits but also puts each unit through a battery of testing inside a full-scale wind tunnel to ensure vehicle dynamics and wind resistance is achieved on the track. The addition of dry carbon under-paneling finalized the Impreza before the body was shipped off to the painters to receive a fresh coat of custom pearl-orange paint. With the return of the chassis, the weight loss continued as acrylic windows were installed on all corners of the car. Final weight after modifications was recorded at 1096kg (2416 lbs), a significant change from an average U.S. spec Impreza STi which often tips the scale at over 3263bs. As the December 8th Super Battle began to slowly creep up on the calendar, the president of Prova, Shinichi Yamamoto, made a call to his driver and 2005 class 2 Super Taikyu champion Toshihiro Yoshida. The Arise team was confident in its ability to crush all the competitors while legitimately challenging the course record.