Post by ah-long on Nov 30, 2005 23:10:08 GMT 8
Nobushige Kumakubo Takes Four Wheels For One Hell of a Slide Ride
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 Profec 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.
Since the original Subaru engine layout is set up for all-wheel drive, JUN had to convert the car to FR layout by making a custom bell housing adapter for the Hollinger 6-speed sequential transmission. While the engine uses an Ogura Racing Clutch lightweight chromoly flywheel and clutch combo for the EJ25 Impreza for quicker revving, JUN had to fabricate a custom one-off drive shaft to connect the Hollinger tranny to the differential, which is actually a Skyline GT-R unit and a Cusco LSD installed inside the pumpkin.
JUN also customized the intercooler to fit the Impreza using a Trust core, then welded up custom intercooler piping, using 60-70mm pipe sections. The oil cooler chosen was also a Trust unit, with 16 rows to keep the car running cool at high rpms.
The radiator setup, however, is pretty different, and always amazes people the first time they lay eyes on the car. The radiator itself is a 3-row unit, which was special ordered from Yashio Factory in Saitama, which isn't too far from JUN. The engineers at JUN custom-mounted this Yashio radiator in the trunk of the Impreza since there wasn't much room left in the engine bay. To make this work, JUN had to cut the side of the car and add custom air scoops in the rear doors of the Impreza, which would use metal ducting to route air to the radiator while Kumakubo has the car sideways during a high-speed drift. Since JUN customized the M-Sports wide-body panels for the car, the rear fender scoops were originally twice as big, but when Kumakubo saw the huge intake scoops, he thought it looked a bit too bulky, and asked the mechanics at JUN to make it smaller. Since the customer is always right (especially when that customer is Nobushige Kumakubo), the JUN technicians reduced the size of the scoops and vents, and found that there were no problems with the water temperatures even though the scoops were smaller, so it seems the orange bear got his way after all. Other than the custom air scoops on the side of the car, the rest of the aero kit (front/rear bumpers, side skirts, hood, and fenders) was made by M-Sports, which is the same company who sponsors Kumakubo's close friend and Team Orange counterpart, Kazuhiro Tanaka. When I asked Kumakubo's chief track support mechanic, Igusa, why M-Sports chose to make only the Impreza's hood and front lip spoiler out of carbon kevlar, I was quickly corrected. "No, no, Antonio; it's not Kevlar. Technoora." I didn't understand. I thought he was teaching me the Japanese translation for Kevlar. "Nani? Wakaranai. What did you say? I don't understand," I responded. Igusa continued to explain that Kumakubo is sponsored by a company named Teijin, which makes this fabric product called Technoora, a strong fabric that's like carbon Kevlar, but is much stronger, lighter, handles impact better and is harder to break. Apparently, Kumakubo's yellow-hued hoods on his S13 K-truck, S15 Silvia, and WRX have all been made out of this new Technoora material. All the while, most of us thought it was some sort of carbon kevlar! Kumakubo seems to be the first person to use Technoora for automotive purposes, and innovated its use in motor sports.
For the rest of the chassis customizing, JUN fabricated a one-off chromoly roll cage and spot-welded areas of the interior, around the doors, engine bay, and trunk area. Kumakubo also asked that JUN install a set of air-jacks on the car, because he thinks the air jack systems on Super GT cars are so cool, not to mention convenient. Kumakubo didn't want to wait around all day for Igusa to manually jack up each end of the car. When he wants those tires changed, he wants it done ASAP. Everyone knows the key to control when drifting is a good suspension. For his footwork needs, Kei Office custom made a set of coilovers to match Kumakubo's spring rate and dampening specifications, using Swift springs and DG5 dampers. The rest of the Impreza's suspension components are pretty much all made by Cusco, from the under chassis bracing to the rear arms and pillow ball links. Even all the bushings on the car are pillow ball-type from Cusco. The only exception is the standard STi strut tower bar, which has a tow hook welded to it. This tow hook sticks out of the hood for ease of access.
Braking is an important part of drifting, when it comes to adjusting drift angle and driving line. To ensure the brakes would perform optimally, Kumakubo requested stainless steel brake lines and Endless brake pads to be installed on his standard OEM brake rotors and calipers. It just goes to show that huge brake rotors and 6-piston calipers aren't absolutely necessary for drifting, although it does make things easier sometimes. The car sits on wide Enkei RPF1s, with 255/40R17 Advan Neova tires mounted on the 17x9.5J front wheels, and 265/35R18 Neovas mounted on the 18x10.5J rear wheels.
Inside the cockpit, the Impreza is all business. The rear seat area was gutted and replaced with the huge ducts which lead from the rear doors to the rear mounted radiator. The only thing inside the car, aside from the custom made rollcage, are the bright red Bride bucket seats and Teamtech camlock seatbelts. Kumakubo installed a Key's Racing 350mm suede steering wheel with quick release hub, along with Stack gauges for instrumentation. To add to the Impreza's "rally look," JUN installed some rally style metal footplates on the floor of the car.
While I was shooting photos of the car, Kumakubo asked if I wanted to go for a ride in the Impreza. Uhmm, let's see - how do you say, "Hellfockeryeah!" in Japanese? I've always wanted to ride with the Tsuisou King (Tsuisou meaning "tandem") himself on his own stomping grounds at Ebisu's Minami Course, where the D1 competition is held. As I strapped myself into the Bride buckets, I asked Kumakubo how he likes the Impreza in comparison to the Ichi-go (his famous S15 Silvia). Kumakubo smiled and explained that, "compared to the Ichi-go, the driver's position is different in the Impreza. It is more centered towards the middle of the car, further from the engine." Since his seating position is different, when he would drift the Impreza, he used to think that it had a lot more angle than it actually did. In fact, it took several of his friends watching his runs from outside the car to convince him that the angle was actually shallower than he thought. Kumakubo explained that this is a situation that is also common with the 350Z and G35. Now that he has been able to overcome this issue, he can now achieve a deeper angle in the Impreza than he ever could have gotten in his S15.
Riding with Kumakubo on his home court was awesome, to say the least. He blasted through the course full throttle, coming closer and closer to the pit wall, and then with a flick of the steering wheel, he would send the Impreza into what seemed like a violent left hand spin at over 160 kph (100 mph), but Kumakubo's mastery behind the wheel is unequaled. He deftly counter-steered to the right and feathered the throttle, controlling his ferocious orange Impreza at high speed, with a line so perfect that the left front tire would pass over the rumble strip every single time. We were not alone on the racetrack when Kumakubo took me for this ride along. There were about 15 cars out on the course, with a mix of S13s, S14s, AE86s, assorted Skylines, and Toyota Mark IIs. However, the less experienced drivers on the course couldn't help but be intimidated by the WRX's menacing HID headlights rapidly approaching in the rearview mirror, and while the gold and brown graphics depicting a ferocious grizzly bear on the side of the Impreza have a sort of "regal" look to them, the graphics also kind of screamed "get the hell out of the way" at the same time. One by one, the other cars on the track either nervously spun, or pulled to the side, bowing to the king as he passed. Amazing would be an understatement.
