German Car Zone

bmer · 08-20-2008, 04:07 PM

SMALL VOICE, BIG STICK

A few short years ago, the notion of a diesel-powered supercar would have seemed preposterous. Today, Audi's R8 V12 TDI concept blows this notion away with a thunderous 738 lb-ft of torque.

By SEBASTIAN MARTIN
Photography by THE AUTHOR

At first, it appears all too familiar. You slide into the Audi R8 and sink into the narrow sport seat with its supportive side bolsters. Yet, noticing the red starter button on the steering wheel makes you realize that you haven’t ventured inside the familiar version of the supercar from Ingolstadt. You push the button and the mid-mounted engine leaps almost silently to life, without the slightest shudder. You have to put your ear right up against the opened engine compartment to make out that slight metallic knocking, the sure sign of a diesel engine—in this case, the first self-igniting powertrain ever inside a supercar.

Generating a mighty 738 lb-ft of torque between just 1,750 and 3,000 rpm, this 6.0-liter V12 turbo-diesel catapults the R8 onto a whole new level of performance. Yet diesel power offers a fuel-efficient and eco-friendly alternative to gasoline-fueled engines.

Purring like a cat at idle, the big V12 TDI gives a razor-sharp response to a swift tap on the gas pedal, displaying a measure of immediacy previously unknown in turbo-diesels. It has the manners of a racing engine with lightweight moving masses, yet this 500-hp V12’s hardware has more in common with Audi’s family of V6, V8 and V10 street engines than the 650-hp 5.5-liter V12 that has powered the R10 race car to back-to-back wins at the 24 Hours of Le Mans. Other than a shared 60-degree cylinder angle, these two engines are very different.

Weighing in at a reasonable 750 pounds, the 6.0-liter V12 has a cylinder center-to-center distance of 90 mm, just like the other street TDI engines. With a bore diameter of 83 mm and a 91.4 mm stroke, the piston dimensions are in fact identical—a product of modular engine construction. The engines share materials, as well. As with its V6 and V8 siblings, the V12 TDI has a cast-iron crankcase made with weight-optimized and wear-proof vermicular graphite—the race engine’s block is aluminum. Although this prototype V12 TDI is fitted with the R8’s existing 6-speed manual transmission, the production version will have a 7-speed double-clutch gearbox with steering wheel-mounted paddles.

As soon as the turbine-like engine channels its might to all four wheels, the tires claw themselves into the asphalt and propel the R8 V12 TDI forward with rocket-like force. This explosive takeoff is a spectacular celebration of diesel technology, yet is done without a supercar’s typical signature tune. To be precise, the R8 does it all in virtual silence. No other high-performance automobile compels the driver to keep an eye on the tachometer to such a degree; the engine hum is too faint to rely upon hearing alone when shifting gears, and the 4,200-rpm shift point comes up almost instantly.

Audi claims the R8 V12 TDI races from 0 to 62 mph in just 4.2 seconds, virtually the same as a Ferrari F430. However, compared to the acoustically expressive Ferrari, the Audi is decidedly reserved. It is the embodiment of technical perfection, with more emotive qualities pushed to the sidelines.

The acoustic deficit is the result of extensive measures taken to reduce emissions. The exhaust system includes multiple catalytic converters and particulate filters. In addition, the Adblue system injects small amounts of urea. In the hot exhaust, this fluid breaks down into ammonia, which in turn splits the nitrogen oxide into nitrogen and water. The urea is carried in an ancillary tank at the rear on the right-hand side, and only has to be topped up once every service cycle. The complex system satisfies Euro 6 emission standards, which are expected to come into effect throughout Europe in 2014. But will it satisfy supercar buyers?

Audi is fully aware of the R8 V12 TDI’s potential auditory stumbling point, and is ready to address it. “Should it turn out that the R8 driver would like more sound, then this could be modulated,” says powertrain expert Wolfgang Hatz. How this could be accomplished, he doesn’t say.

In the absence of acoustic stimulation, we were forced to focus on the R8 V12 TDI’s exceptional driving dynamics and the perfect interplay of its mechanicals. As with the gasoline-powered version, the diesel steers into bends with great precision. Although the chassis has grown in length to accommodate the longer engine, the weight distribution is virtually unchanged—46/54 percent—as the V12 extends further forward than the V8. Also like the standard R8, the super-diesel is a smooth performer. Its electronic damper system produces a sporty yet never harsh ride quality, ensuring a high level of comfort.

Our first excursion on a North American highway passes without tasting the thrill of the R8’s top speed, which Audi’s engineers tell us is near the 200-mph mark. But even at much lower speeds, our pleasure is marred by the tiresome noise of air rushing across the two transparent roof panels and into the centrally located NACA duct. We felt like we were caught in a wind storm. The aerodynamics clearly require some finishing touches, a point that Audi assured us will be addressed.

Some aero changes are already visible. For instance, the base of the “side blades” have been extended to create larger air scoops. All the grilles use the trapezoidal material shared with Audi’s current RS vehicles. A front splitter and a rear wing increase downforce, as well as visual excitement.

The R8 V12 TDI is the first supercar that builds on the appeal of eco-friendly driving—which may, of course, fuel many a debate. After all, supercars are seen as fun machines created to continuously test and extend both physical and human boundaries while showing no respect for limited resources. In contrast, Audi’s mid-engine supercar rises to the challenge with political correctness. The sales figures will tell whether this path can compete with the allure of more emotional machinery.

Small-scale production of the R8 V12 TDI should commence in 2010—but not before the release of the 4.2-liter R8 V8 TDI aimed to produce 360 horsepower and over 550 lb-ft of torque. The V8’s unlimited production is due to start in 2009. This will be followed by a diesel-powered TT.

More than any other manufacturer, Audi is committed to making diesel-powered sports cars socially acceptable. Now, if it can just turn up the volume.

SCI Magazine

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