First Look: Audi R15 Sport Prototype

Rex Roy
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Audi did it again. The company that set the racing world on its ear by launching a successful diesel racing program in 2006 just introduced its second-generation race car - the R15 - at the 12 Hours of Sebring, and won it all.

Audi Motorsports offered us a close look at the radically different racer at its Sebring debut. We had the opportunity to see the all-new Audi R15 and talk with engineers about the car and how Audi's current racing program directly impacts their diesel engine development.

Audi began racing diesel-powered cars in 2006 with the introduction of the R10, powered by a 5.5-liter twin-turbocharged V-12 diesel. The R10 left a permanent mark on the sport, especially after it garnered victories at the 24 Hours of Le Mans in 2006, 2007, and 2008.

The new R15 is a completely different car. Dr. Wolfgang Ullrich, the Head of Audi Motorsports explained in a pre-race interview, "Our goal was to increase this car's efficiency in every manner, but to do that, to a certain extent, we followed entirely new routes."

That included an all-new approach to aerodynamics. The R15's fascia sports a taller nose than the R10, which actually works in the car's advantage. The wide openings in the R15's nose lead to channels that move air through the car's body, as opposed to directing it over the car. The new design is effective at reducing drag, but it also increases the R15's downforce.

Additional downforce comes from the revised (and somewhat unusual) rear wing. Unlike most other spoilers, the R15's rear wing is mounted via its top surface, not the bottom. Ullrich noted "it is from the bottom of the wing from which we get our downforce, so we wanted the bottom surface clean."

According to Ullrich, aerodynamics also drove the change from the R10's 5.5-liter V-2 to the R-15's new 5.5-liter, twin-turbocharged V-10 diesel.

"By eliminating two cylinders," he said, "we were able to shorten the engine by 10 mm. This aided in a ten percent weight reduction, and better aerodynamics because of the smaller engine package."

Although it lost two cylinders, the new engine isn't a drastic change from the R10's V-12 unit. It's still configured in a 90-degree V, runs no faster than 5000 rpm, and is remarkably quiet at full throttle.

Over the course of the race weekend, we noted a marked difference between the sound of the R15 at speed and other cars on the track. GT1 Corvettes sound like proper American sports cars, complete with a thunderous V-8 exhaust note. The GT2 Ferrari 430 GTs scream by with a high-pitched Italian wail. Curiously, the 600+ hp Audis streak past, making almost no noise at all.

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