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2007 Subaru Impreza WRX STi - Japan's Dream Team Collaboration

Tomei/Cusco/Voltex Team Tarzan Impreza

Dino Dalle Carbonare
Jan 1, 2009 SHARE

Have you ever asked yourself just how much work goes into build-ing a serious time attack machine? We aren’t talking about bolting on parts from a tuning catalog, but a full-on, top-spec professional project. The car you see here is the perfect example of such a build, and this is the first time this car has graced the pages of any magazine. We teamed up with the guys at Tomei, Cusco, and Voltex to bring you an insight on how this new Team Tarzan Time Attack GDB Impreza has come to be.

It all started last year when Eiji Yamada, aka Tarzan, approached Tomei about teaming up together to create an all-new time attack car. Having been involved in the Japanese time attack scene for years, Tarzan decided this new ride would be specifically built to compete here in the U.S. in both the Redline and Superlap Series. Think of it as a new challenge, something he wanted to approach with full backup from the best Japanese companies. It wasn’t long before Cusco and Voltex came on board, as well as Hankook on the tire front, and the result is nothing short of stunning.

Late last year the build got underway. Tomei sourced a bare GDB Impreza shell and sent it to Cusco where the transformation began. The same guys involved in creating the Super GT300 Impreza where let loose with spot welders, as well as fabricating additional bracing for critical areas. With experience in building a GT car, these guys knew exactly what to do and made sure the whole chassis would be incredibly stiff. A race-spec rollcage was constructed and welded, further helping in the rigidity department, as well as making sure Tarzan is kept safe in case of an accident. At this point the Pianetto air jacks were fitted into position, two at the front and curiously only one centrally mounted at the rear. This was probably done to avoid adding unnecessary weight. A lot of work went into stiffening the front and rear suspension turrets, and modifying the actual wheel arches to accommodate the wider track and bigger wheels. As the chassis prep was being completed the Cusco engineers began looking at the front and rear suspension layout. They decided that for this particular application the stock Subaru Impreza arms and geometry just wouldn’t do, so the whole lot was scrapped. Joining the specially set up, Cusco Comp-X adjustable dampers is a series of custom-built links, all connected up to the one-off front and rear hubs. Even the steering knuckles are adjustable and attach to the lower section of the front hubs through custom pivots.

Having pillow-ball connection on each of the lower arms allows for limitless geometry adjustability, and having reengineered everything has allowed the whole roll center to be lower than it would be on a stock car. This greatly improves overall handling balance as well as getting the most out of the increased track and sticky Hankook Ventus Z214 275/35-18 tires. At the rear, it is much the same story with adjustable lower links and tension rods bolted onto the lower part of the custom hubs. Beefy Cusco antiroll bars are used front and rear. At this point it was the turn of the brakes and again, like what we have seen so far, no compromises were made. Straight from the Brembo competition catalog are the eight-pot forged front calipers mated to two-piece slotted rotors. These calipers help keep un-sprung weight to a minimum thanks to their light construction, which also feature ventilated titanium pistons for optimal performance. At the rear, AP Racing four-pot calipers bite down on two-piece rotors, which are the same diameter as the front (ø355mm). Performance friction pads are used at each corner. While the car was at Cusco, Tomei were already underway on the engine build, which is when we dropped over to take a look at the bench dynamometer test.

When we arrived at the state-of-the-art Tomei headquarters, south of Tokyo, the EJ25 was already strapped down in the dyno room. A series of run-in and warm-up procedures were done before going for a full boost, full power run. With over 450 ps and 60 kg being developed, this engine has received some serious attention from the guys at Tomei. Having had much experience in the past by building the motor in the Prova-Tomei Impreza demo car, they knew exactly what needed to be done to take the EJ one step further. The main goal was to not only create a more powerful package but to fine-tune its response and midrange characteristics that are so often ignored in track-going engines. It all started with the base EJ25 engine, which was stripped down and prepared for the build. For this project a special set of internals were built, starting with the fully counterweighted and balanced competition crank, the H-beam connecting rods, and the special forged 99.75mm pistons. Once this was done, the little boxer heads were taken care of with some top-of-the-line Tomei parts. To fit the special beryllium valveguides and valve seats, the heads were heated in an oven for some time so that the alloy would slightly expand. Once this was done, the guides and seats were dipped in liquid nitrogen so the metal would contract, allowing for an easy fit into the heads. Once back to room temperature they would embed themselves perfectly into the head. The stock valves were used since they were well up to the job, even on a highly modified engine, while some porting was done to guarantee the best flow. Specially milled Tomei Poncams were thrown in at 250 degrees and 9.6mm lift on the intake, and a slightly more aggressive 256 degrees and 9.8mm lift for the exhaust side. These were then mated to Tomei adjustable cam pulleys along with a Tomei timing belt and guide. The 0.7mm think metal head gaskets were used to seal the heads to the horizontally opposed block giving an 8.5:1 compression ratio, ready to take the 1.6 bar of boost. This force-feeding was taken care of by the Garrett GT3076R mounted on custom 4-into-2-into-1 equal length header.

Boost control is looked after by the HKS external wastegate while gases are dumped into the Tomei custom front pipe and then onto the one-off titanium system, built by Hatanaka-san at Tomei. Tomita-san took care of fabricating the custom aluminum piping kit for both the intercooler piping as well as the short intake pipe where the K&N cone filter is fitted. A Calsonic front-mount radiator has the job of cooling the intake charge before sending it onto the stock intake plenum. Fuelling is taken care of by a Bosch motorsport fuel pump that sucks gas from the 20-liter racing tank in the trunk and sends it on to the twin Tomei billet rails via braided lines. These feed the four 850cc/min injectors while the factory FPRs do a good job of keeping pressure under check. Fuel and ignition maps are all handled by the MoTeC M600 ECU, which was custom wired into the Impreza. A massive oil cooler with its own custom air guide, along with the racing radiator, keep the engine within operating temperature, even when pushing hard out on track. The monster midrange torque of the EJ25 is sent through the Cusco twin plate metal clutch to the Cusco Dog engagement gearbox. This five-speed transmission has been used extensively in rally competition and is perfectly suited to a time attack car like this Team Tarzan Impreza. Easily fitted inside the factory Subaru gear housing, the Dog gearbox has more evenly spaced ratios to help get the most out of the increased power while cutting down in shift times dramatically. When we saw the car being tested at Fuji Speedway, Yamada-san was savagely banging the gears in, making it sound just as fast as a sequential box. Cusco went all-out on the driveline with a one-way limited-slip differential up front and a one-and-a-half-way limited-slip differential at the rear, while the center differential is fitted with a special Cusco Active Control DCCD unit so Yamada-san can adjust the front/rear torque split according to varying tracks and conditions. A carbon-fiber (CFRP) propeller shaft helps keep rotational masses to a minimum, furthering the response. With such an impressive mechanical base it was then onto Voltex in Suzuka who took care of the exterior of the car.

Voltex was the perfect company to join Tomei and Cusco because their attention to detail is mind-blowing. Having run Voltex parts on his Cyber Evo time attack machine, Tarzan knew that Voltex would do a great job with the Impreza. They began in the Voltex workshop, shaping the molds for the body panels according to the agreed-on designs. The requisites were simple: To create an aerodynamic and aggressive design that would generate the high levels of downforce needed in a car of this nature. Once the primary body shape was completed, the car was put in a wind tunnel and meticulously checked for overall flow and of course measured for downforce. With this done the body panels were created, giving the Impreza an extremely purposeful silhouette. It all begins with the front bumper, which utilizes the factory Subaru grille but combines it to a wider, more aggressive stance, as well as a massive integrated front spoiler. The whole piece is made in dry carbon, as is the spoiler slash diffuser. This stretches all the way under the engine to smooth airflow, and protrudes well over the dimensions of the car both in the front and at its sides. Voltex had to create a small aluminum subframe to hold the diffuser in place, which is where all of the front downforce pushes. At 100 km/h, the massive front scoop already generates around 40 kg of pressure, which is just what you need to corner on rails. The front fenders, again made in dry carbon, push the dimensions of the car out by 50mm on each side, allowing for the same increase in front track. The carbon aero hood does a great job of expelling heat from the engine bay, without disrupting the car’s airflow. Angular side skirts accentuate the profile of the Team Tarzan Impreza while the massive rear carbon overfenders complete the race car look. Just like at the front, a 50mm increase was achieved, helping push those 18-inch Volk Racing TE37 wheels out further for better handling. The factory rear bumper is joined by the lightweight carbon trunk lid, which is secured to the car through a series of racing catches. The hook-up point for the gas jack system is on the left side of the lid, and can literally lift the car in five to six seconds when plugged into a gas tank. Rear downforce is handled by the massive carbon spoiler, which at 100 km/h can generate 10 kg of force. Small carbon mirrors were made up to aid in additional weight saving, much like the acrylic windows. In fact, with all the exotic carbon bodywork and the work Cusco did on the chassis, the weight comes in at 1,060 kg, which is simply impressive. This is also achieved thanks to the spartan layout of the interior.

Open the driver side door and you are met with the twin crossbars of the rollcage. There isn’t much else to see except the mere essentials, like the lightweight carbon-Kevlar Bride bucket seat and the Sparco steering wheel. To move the driving position as far back as possible, the steering column was extended and a custom console made up where the MoTeC data logger LCD screen is fitted. Since being in this extended position would never allow Yamada-san to be able to reach the stock pedals, a Tilton adjustable pedal box was thrown in, which helps in giving the driver the perfect driving position. Only an HKS Knock Amp Meter has been fitted as additional instrumentation because all the parameters you need to care about are visualized via the MoTeC display. The controls for the center differential have been positioned within easy reach along the transmission tunnel.

The Team Tarzan Impreza is now being shipped to the U.S., where it will arrive in time to enter the Super Lap Battle finals on Nov. 12 at Buttonwillow. The car will then remain in the U.S. and participate in both the Super Lap Battle and the Redline Time Attack in 2009. Tarzan is excited to take on the U.S. tuners and to see how the best from Japan will fear against the best from our neck of the woods.

Specs
Max Power:
Over 444 hp
Max Torque:
Over 434 lb-ft of torque
Max Boost:
1.6 bar
Compression ratio:
8.5:1
Weight:
2,337 pounds

Turp_0901_104_z+subaru_impreza_wrx+cornering Photo 32/45   |   2007 Subaru Impreza WRX STi - Japan's Dream Team Collaboration

Engine:
Tomei Genesis Prototype TA spec EJ25 base
Tomei prototype forged pistons (ø 99.75 mm)
Tomei forged H-beam connecting rods (130.5mm center distance)
Tomei con-rod bolts
Fully counterweighted and balanced forged crankshaft (79mm stroke)
Fully ported GDB heads
Tomei beryllium valve guides
Tomei beryllium sheet rings
Tomei oval-shaped wire core valvesprings
Tomei Poncam 250-degree duration, 9.6mm lift (IN), 256-degree duration, 9.8mm lift (EX)
Tomei prototype adjustable cam pulleys
Tomei timing belt and timing belt guide
Tomei prototype metal head gaskets ø101.2mm, 0.7mm thick
Tomei oil pan baffle plate
Tomei Expreme 4-into-2-into-1 equal length headers for single-scroll turbine
Garrett GT3076R
HKS external wastegate
Tomei custom front pipe
Tomei custom titanium exhaust system (Hatanaka spec)
K&N cone filter
Tomei custom intake pipe (Tomita spec)
Tomei custom intercooler piping kit (Tomita spec)
Tomei blow-off valve
Calsonic front-mount intercooler
Racing radiator
Cusco radiator shroud
Oil cooler
Racing 20-liter fuel tank
Bosch Motorsport fuel pump
Braided fuel lines
Custom collector/swirl tank
Tomei billet fuel rails
Tomei 850cc/min injectors (x4)
Tomei custom oil catch tank (Tomita spec)
Tomei signature blue engine cam covers and intake plenum
MoTeC M600 ECU

Transmission:
Cusco Twin Metal twin-plate clutch
Cusco Dog H-pattern five-speed transmission (internal type)
Cusco one-way Type MZ front LSD, one-and-a-half way Type
MA rear LSD
EMCD and Cusco Active Control DCCD
CFRP propeller shaft

Turp_0901_107_z+subaru_impreza_wrx+side_view Photo 33/45   |   2007 Subaru Impreza WRX STi - Japan's Dream Team Collaboration

Suspension & Brakes:
Cusco Comp-X adjustable dampers
Cusco adjustable top mounts
Cusco one-off front and rear hubs
Cusco pillow-ball lower front arms
Cusco one-off adjustable steering knuckles and pivots
Cusco front and rear antiroll bars
Cusco pillow-ball rear arms
Cusco pillow-ball tension rods
Brembo Racing forged eight-pot racing calipers (front)
Brembo ø355x28mm two-piece grooved rotors (front)
AP Racing four-pot calipers (rear)
AP Racing ø355x22mm grooved rotors (rear)
Performance Friction brake pads

Wheels & tires:
Rays Engineering Volk Racing TE37 9.5JJx18 +22 (front and rear)
Hankook Ventus Z214 275/35-18 (front and rear)

Exterior:
Full custom Voltex carbon widebody kit:
Voltex one-off carbon front bumper
Voltex custom carbon front wider fenders (+50mm on each side)
Voltex custom carbon front spoiler and underengine cover
Voltex carbon aero hood
Carbon-plated off-stock intercooler guide opening
Voltex carbon side skirts
Voltex custom carbon rear overfenders
Voltex custom carbon trunk lid
Voltex carbon rear spoiler
Carbon exhaust bumper protector
Carbon side mirrors
Lexan glass except for windscreen

Interior:
Fully spot-welded chassis
Custom reinforcement added to high-stress areas
Cusco welded-in racing rollcage
Pianetto air jacks (two front, one centrally mounted rear)
Bride Low Max carbon-Kevlar full racing bucket seat
Takata racing harness
Tilton adjustable pedal box
Sparco alcantara racing steering wheel
Custom extended steering column
Custom steering boss
MoTeC data logger LCD display on custom carbon console
Fully stripped factory dashboard
Custom switch console on center tunnel (fuel system/DCCD controls)
HKS Knock Amp Meter
Lightweight battery relocated to passenger footwell
Fire extinguisher in passenger footwell

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Sources

Tomei Powered USA, Inc.
Lake Forest, CA 92630
949-855-6577
http://www.tomeiusa.com
Cusco
n/a, AK
027-352-3578
http://www.cusco.co.jp/en
Voltex
Suzuka-shi, Mie-ken, Japan, CA
http://www.voltex.ne.jp
By Dino Dalle Carbonare
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