In December of 2004, more than 35,000 people gathered at California Speedway at Fontana, California for the GT Live weekend, and witnessed the D1 "USA vs Japan" drifting competition where a bright orange S15 Silvia driven by Nobushige Kumakubo, the leader of the world famous Team Orange, triumphantly emerged from the clouds of tire smoke with a First Place win.
In the days and weeks after, many of the fans stateside couldn't stop talking Kumakubo's win and about how much fun they had at the event. However, when Kumakubo was talking privately to his most trusted friends, he had something else on his mind. He just couldn't stop talking about the new car he was building for competition in the D1 series-a rear-wheel-drive Subaru Impreza WRX STi.
When I first heard he was planning to build a WRX as his new drift car for competition, I was quite surprised, so I had to ask the question: "Why? What made you choose a WRX?" To answer my question, he replied, "Well, you've seen the huge stack of Japanese drifting and rally magazines in my office. I have always thought rallying was cool, especially since Ebisu is covered with snow in the wintertime. And since there are a lot of people who have Imprezas now, I wanted more Subaru owners to come and drive at Ebisu." Kumakubo's statement and his outlook on the Impreza were both very interesting to me, especially since he's so diehard about drifting, and most of the drifters in Japan naturally adhere to front engine, rear-wheel-drive platforms instead of all-wheel-drive systems.
To put some things into perspective, Nobushige Kumakubo is one of the most well-respected and well-connected drifters in Japan, not to mention one of the wealthiest. Technically, he could have built whatever he wanted as a drift car-V35 Skyline, BMW Z8, Ferrari Enzo, Bentley, whatever. The Kumakubo family owns quite a bit of land in Fukushima, Japan, which, by train, is roughly 3 hours north of Tokyo. An unspoiled gem of the Japanese countryside, Fukushima is abundant with rice paddies, mountains, and green rolling hills. However, for car enthusiasts, Fukushima's top attraction has nothing to do with lush forest areas or mountains. In this area it's all about the twisty mountain roads! With this in mind, Kumakubo planned and designed his own version of motorsports paradise called Ebisu Circuit on a group of mountains owned by his family. In fact, Kumakubo went on to explain that he not only designed the course on paper, he also drove the bulldozer himself! Known by the hashiriya (street racers) as "The Holy Land of Drifting," Ebisu Circuit is now legendary in Japan because of all the numerous drifting events that have taken place there over the years-Carboy Dori-Con, BM Cup, D1GP, Big X, and others. This new WRX from Team Orange is significant because it is the first time ever that a Subaru will be used in D1 competition. Therefore, before Kumakubo could transform the car into a vehicle competitive enough to battle the other high-tech machines in the series, a ton of research and development was necessary. For the job of taking his brand new all-wheel-drive Impreza WRX STi and making it into a front engine, rear-wheel-drive drift machine, Kumakubo chose to call upon the services of his longtime friend, Susumu Koyama, at JUN Auto Mechanic in Saitama, Japan. In case you were wondering, yes, this is the same JUN who made the Hyper Lemon S14 Silvia, Bonneville Z32 Fairlady 300Z, and Bonneville Top Speed JZA80 Supra that were brought to the United States in past years. Again, with Kumakubo's vast resources in Japan's automotive industry, it's no doubt that just about every company would be interested in working with him on building a new drift car, especially something this remarkable. That's why, as we were driving through the twisty downhill service road leading to Kumakubo's office at Ebisu's East Course, I just had to ask the question again, "Why JUN? What made you choose it over all the other companies out there?" Kumakubo's answer was a simple one. "When it comes to making parts and building a race car from scratch," he explained with a smile, "JUN is the shiznit." Since building this new car for a high-profile driver like Kumakubo was a huge undertaking, Koyama-san and the JUN mechanics put all their other projects aside and focused all their efforts on Kumakubo's Impreza. This process took them roughly six months of non-stop work.
Koyama-san and his staff at JUN started off by acquiring a 2500cc EJ25 engine from the USA, which has more torque to start with than the motor in their Japan-spec Impreza. However, to build this motor into the 500-plus horsepower beast that Kumakubo wanted as his powerplant, the engineers at JUN had to completely rework the engine. The factory engine internals were tossed in favor of JUN original parts-custom crankshafts, 8.2:1 forged pistons, and forged connecting rods, changing the piston bore to 100 mm and giving the engine 79 mm of stroke. An EJ25 standard 1.4mm head gasket was combined with JUN custom camshafts and valve springs to complete the head,although the stock valves were retained.
On the intake side, a Trust Airinx air filter was used, along with a factory throttle body. However, on the exhaust side, the factory exhaust manifold was combined with JUN TD06 turbine adapter, fitted with a TD06 SH25G turbo. When paired with an E-01 boost controller and Type R wastegate from Trust, this setup gives Kumakubo up to 1.76 bar of boost, although he usually only runs the car at around 1.5 bar. When Kumakubo builds his cars, he wants only the best. Therefore, it was only fitting that he used an exhaust system from Fujitsubo, Japan's top manufacturer of exhaust systems and headers. The exhaust starts out at 60mm at the down pipe, and then expands to 76.3mm at the main pipe, then 120mm at the exit for maximum exhaust flow.