Tucked away under the lights at this year's Tokyo Auto Salon in January was a very interesting prototype. Looking like something out of a German DTM series, the Lexus IS Racing Concept was on display next to the new IS-F. The specks of information from the guys at Toyota left the crowds perplexed but equally amazed at this mean-looking interpretation of a possible future touring car. Toyota's move was primarily done to get people talking, and that they sure did. All sorts of rumors were started, but it wasn't until a few weeks later that confirmation of a Super GT race car came in. Most assumed it was the car they saw at the Auto Salon, but in fact a private team built the GT300 class contender from the ground up. Behold the mid-engine, Green Tec Kumho IS350.
Wanting to find out more about this outstanding-looking car, we met up with the guys from Team Takeuchi during a closed test run at Fuji Speedway. Built by Shift, this Lexus IS350 shares very little with its road-going counterpart. First off, Super GT regulations allow a certain amount of modifications to be made to the chassis suspension layout, and engine type and position. So when we walked into the pits, we almost didn't recognize what we were looking at. The mechanics were swarming around a semi-deconstructed car with half of its bodywork gone to allow access to both the engine and suspension components.
Super GT allows race teams that compete in the GT300 class no restrictions in engine position, orientation, and type of engine used, as long as it's a production motor made by the manufacturer. On top of this, as long as the center part of the base shell isn't modified, teams are allowed to go crazy on chassis modifications. So it's not hard to understand why Shift dropped the engine behind the driver for optimal weight distribution.
This required some pretty impressive work on the chassis side of things, which started with most of the rear section being cut away and a firewall placed behind the driver. Then, it was on to the construction of the complex tubular frame, which is fixed onto both the shell and the Xtrac transaxle six-speed sequential transmission. So effectively the gearbox is used as a part of the chassis and as a mounting point for the pushrod-type rear suspension layout.
The dry-sumped RV8J engine is extremely low within this rear tubular subframe-and yes, this is no 3.5L V-6, but a fully race-tuned Toyota 3.0L V-8. Capable of developing a massive 550 ps in Formula Nippon single seaters, the tiny Toyota V-8 has been forced to breathe through 24.8mm air restrictors and has been re-tuned for more midrange power. While 300 ps and 300 Nm might not sound like much, on a fully fledged 1,200kg racing car, it's more than enough to put down some serious times. The RV8J is fed air through a massive carbon roof scoop, which doubles as an airbox. Spent gasses are expelled via a pair of equal-length headers and a straight-through exhaust.
Due to the rather unconventional engine positioning, the bodywork has been engineered to be very easy to remove, so that as soon as the car comes in the pits the mechanics can peal off the rear carbon doors, rear carbon window cover, and trunk lid, giving them access to all of the components. An air jack system allows the car to be lifted up instantly with a small shot of pressurized air.
Much like the engine position, the suspension is free to be modified. Like most teams, Shift opted for a far-better-performing double wishbone layout. Shift created a tubular front subframe, where you'd expect the engine to sit in a Lexus IS, to hold up the initially complicated-looking suspension mechanism. The double wishbones connect to the pushrod system, which in turn pivots to send the suspension movement onto the Quantum dampers. These are mounted vertically for easy access during spring changes, while their reservoir tanks are mounted on the top crossbar. The adjustable antiroll bar is connected to the billet pushrods and fixed onto the main chassis. Taking advantage of the extra space in front of the suspension is the radiator, enclosed in a carbon air-guide tub.
At the rear, it's much the same story with the suspension. The double wishbones (heat shielded with gold to protect them from the hot exhaust) send their movement onto the pushrod billet pivot, which is mounted on the Xtrac transmission mounting points. The Quantum suspension takes care of the damping, while two long tension rods connect to the adjustable antiroll bar. Super GT regulations state that no carbon should be used in the braking system, so the IS350 runs some simple AP Racing six-pot monoblock calipers up front mated to two-piece, ø 380mm grooved rotors. AP Racing four-pot calipers bite down on ø 355mm discs at the rear while Project Mµ supplies the team with racing series brake pads. Using a single wheel nut hub the 11x18 Tan-ei-sya wheels are easily changed at pit stops, while the Kumho tires come in different compounds to fine-tune the handling. Incase the weather changed, Shift also brought some intermediates and wets to the Fuji test run.
The exterior looks like it's been subjected to a heavy dose of steroids with only the overall shape and glasshouse hinting at what the base car actually is. Roof aside, everything you see is made of carbon fiber-the expensive vacuum sealed and pressure cooked variety. The car has obviously been widened considerably to contain the new front and rear tracks, which measure 1,895mm at the front and 1,650mm at the rear. At the front end only the stock Lexus grille remains; everything else is redesigned including the headlights, which feature two small round reflectors. The massive air dam built into the front bumper feeds the large scoop, which cools the radiator. At each side smaller intakes channel air directly to the front rotors to keep brake temperatures down.
In typical Super GT style, it seems the car has had a small portion of the bodywork cut from the ground up and dropped over the massive Kumho slicks. The result is massive wheel arches that protrude well above the hood line, creating the most menacing front end. The paper-light carbon hood features openings that not only expel hot air from the radiator but also help smooth airflow over and around the car.
The rear doors, like the front doors made from carbon fiber, serve solely as a kind of engine hood to allow access to the mechanicals. The rear fenders sport an angular design that merges into an aggressive series of side canards, which drop around the wheel arch before ending on the corner of the bumper. These are said to help massively in rear downforce, helping the IS carry speed through corners. Peeking through the lower section of the bumper and the rear carbon diffuser are the twin exhausts that seem to burn more and more paint off the rear bumper with each track outing. The massive carbon rear wing, adjustable in various angles, is fixed directly onto the rear section of the chassis to transmit its downforce where it matters.
Helping the driver see what's going on behind him is the Panasonic rearview camera, which sends video signal to the LCD screen in the cockpit. (The interior resembles more of jet fighter cockpit than the inside of a car.) The dash is made from carbon fiber and covered with any-reflection material, which resembles velvet. The main instrumentation is fixed directly onto the Sparco steering wheel, while the center console and transmission tunnel are covered with miscellaneous switchgear and controls. The big metallic gearlever actuates the Xtrac transmission, while two smaller ones allow the driver to adjust the antiroll bars on the go. An adjustable pedal box helps the driver find the most comfortable setup. The passenger side holds most of the electronic control modules of the car and various timing and data loggers, helping to balance the weight of the driver.
Team Takeuchi with the Shift Lexus IS350 debuted at the second round of the '08 Super GT season. Main driver Takuya Kurosawa, son of legendary race car driver Motoharu Kurosawa, and secondary driver Takuto Iguchi were all ready to go, but the car was unable to qualify due to some delays in getting it ready in time. The car returned at Round 3 in Fuji Speedway, where in its debut run qualified 20th with a time of 1'55"243. The race didn't go too well as the car retired due to some trouble. The next round in Sepang will hopefully go better for the Team Takeuchi guys as little gremlins have been worked out.
RV8J naturally aspirated V-8
93mm x 55.16mm (bore x stroke)
24.8mm air restrictors
Carbon roof scoop airbox with panel filter
Straight-through twin exhaust system
Custom racing fuel tank with double high-pressure side-mounted filler valves
Wako's engine oil
Xtrac six-speed sequential transaxle gearbox
AP Racing clutch
Quantum fully adjustable dampers
Various combinations of springs
Double wishbone layout with pushrod damper mounts Adjustable antiroll bars
AP Racing six-pot monoblock racing calipers (front)
380mm two-piece slotted rotors (front)
AP Racing four-pot racing calipers (rear)
ø355mm two-piece slotted rotors (rear)
Single nut hubs
11Jx18 Tan-ei-sya single nut racing wheels
280/710R18 Kumho Ecsta racing slicks/intermediate/wets
Fully custom Super GT GT300 class compliant carbon-fiber body
Adjustable GT wing
Fully bespoke mid-engine layout with transaxle
Tubular front chassis and subframe with pushrod mounted dampers
Tubular rear transaxle based chassis
Air jack system
Separated cockpit from engine room
Fully custom carbon racing interior/dash/center console
Recaro carbon-Kevlar racing bucket seat
Sparco racing steering wheel
Panasonic Strada LCD monitor with rearview camera