Audi's Silver Bullet - The A4 quattro Touring Car
Perhaps the most enticing factor about the Touring Car format is the similarities the racecars hold with the average family sedan parked out in the driveway. Images of early stock car racing come to mind where many companies pitted their road cars, numbers and maybe a few sponsors, emblazoned on the side, against each other in historic places like Daytona Beach.
There's nothing "stock" about today's American NASCAR events. The cars look nothing like their production-counterparts and these rear-wheel-driven behemoths flying around an oval track in all their carbureted glory, bear extremely little resemblance technologically either.
That's not so with a Touring Car
Outwardly, the A4 racecar is very similar to its roadgoing cousin with a few modifications including a large trunk-mounted rear spoiler, low ride height, large 19" OZ alloy wheels and a deep front airdam that must have at least 45mm clearance according to Super Touring regulations.
The Audi factory team cars were painted in the brand's infamous silver color scheme, paying homage to the awe-inspiring Auto Union racecars of the 1930's. The four-ring logo ran diagonally up the side of each car. As with the Audi logo, additional logos from contributing manufacturers such as tires, lubricants, seats and electronics were placed on the car in Audi Sport's signature red hue.
Drivers on Audi's factory teams were distinguished through the use of different colors on their car's exterior rear-view mirrors and additional segments depending on the series. The Audi Sport UK cars also featured "Audi quattro" windshield decals in the driver's color, while German STW series cars featured whole roofs painted in the driver's color.
Though based on an Audi A4 chassis, the similarities are kept to the outside. On the inside, the car is outfitted with a wide range of structural and mechanical enhancements.
To build the race-spec A4 touring car, the chassis is first fitted with a tubular safety cage. The cage, combined with full seam welding, supplies plenty of protection for the driver in the event of a wreck and roughly doubles the torsional rigidity of the chassis. These structural enhancements also have a beneficial effect providing improved handling. Portions of the cage extend throughout the front and rear bulkheads of the car, connecting to the suspension turrets. The end result is an incredibly strong frame that is practically devoid of unwanted chassis flex.
Underneath, the car is equipped with smooth paneling to provide improved aerodynamics over the cluttered underside of the roadgoing A4. This smooth underbelly helps the front airdam and rear spoiler to operate more effectively and keeps the car glued to the track.
Under the hood, the differences between the A4 racecar and the A4 road car are particularly numerous. Standard specification in the Touring Car format is a 2.0-liter, so the car has a modified version of the 1,998cc-inline four-cylinder setup that is subject to explicit specifications. One regulation states that teams cannot alter the position of the valve centers, limiting the size of the valves that can be used, however leaving the specific size and configuration of the valves up to the developer. In Audi's case, this meant 4-valves per cylinder for a 16-valve setup.
Upon opening the hood of an Audi touring car, the most easily recognized difference is the carbon-fiber cam cover. Below, the engine is controlled by a Bosch Motronic system, lubricated through a dry sump setup utilizing Castrol fully synthetic oil and limited to 8500rpm. Exhaust exits through a three-way catalyst.
With regulations in mind, every possible modification is made to the engine in an effort to optimize power and reliability as much as possible. In full race specification, the modified engine produced 296bhp at 8,250rpm and 188lb ft torque (225Nm) at 7,000rpm. For the 1997 season, power was bumped up to 305bhp at 8,250rpm and 217lb ft torque (260Nm).
The transmission is a 6-speed sequential unit that allows for clutchless shifting. The gearshift is moved backwards for upshifts and forwards for downshifts. Though that sounds similar to Audi's Tiptronic transmission, the similarities end there. While the Tiptronic transmission is an automatic programmed to change gears based on driver inputs, a sequential shifter is a manual transmission with a hydraulically actuated clutch allowing quicker shifts than either a manual or Tiptronic could provide.
The transmission was augmented to handle the increased power output of the A4 Touring Car's engine and mated to a single dry plate clutch made of carbon fiber. In addition, the center, front and rear differentials of the quattro system have been strengthened to help reliably put the power to all four wheels.