2008 Audi R8 TDI Le Mans

Don Sherman
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John Roe

The Liason of Audi's R8 supercar with any diesel engine seems as ludicrous as an Obama/Clinton presidential ticket - until you know the backstory. Two years before Oldsmobile poisoned the diesel well, Audi and Volkswagen began studying how to properly build such engines. After thirteen years of effort, TDI (turbocharged direct injection) diesels were ready for sale. And following two decades of success with TDI diesels in Europe, Audi is finally ready to join its corporate sibling, Volkswagen, by offering TDI engines in the United States.

To give Audi's TDI the U.S. initiation party it deserves, one mid-engine R8 was spruced up with a few custom touches and loaded with a truly awesome turbo-diesel engine. Audi won Le Mans in 2006 and 2007 with a 650-hp, 5.5-liter racing V-12, but the R8 TDI concept car unveiled at this year's Detroit auto show is powered by the next installment in the line of diesels that began with a 2.5-liter V-6 in 1997. On the heels of an outstanding 4.1-liter V-8 diesel launched in 2005, this 6.0-liter V-12 is armed with two of everything: injection pumps, variable-geometry turbos developing 38 psi of boost, intercoolers, and exhaust pipes loaded with the latest catalysts, particulate filters, and urea-injection sanitizers. It produces 493 hp, a hefty 738 lb-ft of torque, and not a hint of smoke, soot, or rattle.

We caught up with Audi's Trojan horsepower project at Sebring after it dazzled Geneva-show visitors with its fresh, brilliant red paint. Decked out in a milled-aluminum miniskirt, assertive side blades, a NACA-ducted transparent roof, a rear wing, and honeycomb grilles, this one-off advances the R8's beauty another notch up the to-die-for scale. The interior is lavishly tailored in soft black leather, hot red stitching, polished aluminum accents, and anodized instrument faces. A rotary control in the steering wheel cranks the engine and adjusts the magnetic dampers.

If only the R8 TDI ran as fast as it looks; unfortunately, it's a eunuch. The A4 transaxle that project manager Uwe Haller selected to make room for the mega engine has only enough torque capacity to support a V-12 restricted to half its potential. A curb weight crowding 4000 pounds is another impediment. But the real reason that we have nothing exciting to report from our 40-mph sprints up and down a short, overgrown runway is that Haller's baby has auto-show obligations. Dents, nicks, and melted clutches would only impede the TDI's worldly progression. We can say that the diesel V-12, which bowed in Audi's Q7 sport-utility vehicle at Geneva in March, is supremely smooth and as quiet as any gasoline V-8 engine. According to Audi product planner Marc Trahan, a 322-hp, 4.1-liter TDI V-8 may be offered as a pick-me-up when the current R8 nears the end of its life cycle. But the diesel devout won't have to wait that long. Audi's TDI show begins next January with a V-6 putting out an estimated 220 horsepower in the Q7.

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