June 26, 2006
Text and Photos by: Chris Ostberg
So Audi takes the checkered flag at the 74th running of the 24 hours of Le Mans race with a diesel powered race car. A diesel?!?! What? Why? How? The answer is simple. After literally dominating the Le Mans prototype class for the last half decade with the seemingly unstoppable FSI powered R8, Audi was looking for a new challenge. With each successful year, the restrictions imposed by the ACO (Le Mans race governing body) seemed to take more and more performance out of the R8 platform. By the end of the R8 campaign, the Audi drivers had been noted to say that driving the heavily restricted R8 was no longer fun. In 2005 trim, the output of the R8 was only about 520 hp. This is borderline competitive in the prototype class. In fact, Audi admitted to having problems overtaking GT class cars (which should be much slower) out on the track. The 2005 Audi team was forced to rely solely on the superior fuel consumption of the FSI engine and the proven reliability of the R8 to take the win. The R8 platform had reached the end of its competitiveness in Le Mans racing. It was time for something new.
Audi has made a name for itself in endurance racing. They are also known to be on the short list of car manufacturers who have the money and technology to campaign a Formula 1 racing program. When asked however, the answer is always the same. Audi prefers to use its resources to compete in racing venues which harbor technology which can be directly applied to road-going models. Audi feels that Formula 1 technology is too far removed from its series production cars to make the development costs worthwhile. Le Mans series racing, on the other hand, has provided a wonderful arena for Audi to develop new technologies which can eventually trickle down to passenger car lines. Two direct examples of this trickle down effect are direct injection (FSI) and biturbo technology.
This brings us back to the why question which we will get to shortly. Audi is no stranger to diesel automobiles. The first production diesel branded as TDI (Turbo Direct Injection) for Audi actually came into production in 1989. This 120 hp/195 ft-lb engine was designed to change the public opinion about diesel power in passenger cars. Since then, Audi has been continuously raising the bar in passenger car diesel technology. Today a full one-third of the cars rolling off Audis assembly line are equipped with a diesel engine. Roughly half of all passenger vehicles sold in Europe are diesel powered. This is obviously a very important niche market for Audi. Every size class from the compact A2 to the luxurious and powerful A8 has been available with an economical TDI diesel engine in markets other than North America.
Audis Never Follow expression holds very true for its diesel offerings. Audi introduced the worlds first production direct-injection diesel car in 1989. The Audi A2 1.2 TDI [link to AW A2 article] boasts many records such as the most aerodynamic production car of its time (Cd of 0.25) and best average fuel consumption of any 4-door vehicle at 2.99 liters/100 km (79 mpg). The current Audi 2.0 liter TDI leads the two liter 4-cylinder class with an impressive 170 hp/258 ft-lbs of torque. The Audi A8 can be equipped with a powerful all aluminum 4.2 liter V-8 churning out 326 hp and a massive 480 ft-lbs of torque. This technological tour-de-force showcases impressive technology (also shared with Audi R10 TDI race car) such has high pressure common rail design (1,600 bar), biturbo parallel turbochargers with dual particle filters on the exhaust side, DOHC heads with 4 valves per cylinder, and the previously mentioned all aluminum construction which results in a remarkable (for a diesel) engine weight of only 250 kg (550 lbs).
With all of this experience making some of the worlds best diesel passenger cars, Audi decided to use its expertise to develop a diesel powered prototype LM P-1 entry called the R10 TDI. Diesel power allows Audi to utilize an entirely different engine rule set granting larger air restrictors (2 x 39.9 mm versus 2 x 29.9 mm for turbo gasoline), much more engine capacity (5.5 liters maximum versus 3.6 liters for turbo gasoline), and higher boost levels (2.94 bar absolute versus 2.67 bar for turbo gasoline). The development cycle of the R10 program was somewhat unique as Audi had to rely first on its passenger car experience to develop the race program. Usually, technology is developed on the racing side before crossing back over to the series production line. Over time, however, the benefits will be seen for the everyday driver as experiences gained campaigning the R10 platform will eventually trickle down back into the passenger car ranks. I would expect to see a new high performance line of diesel engines spawned off by Audi as a direct result of the R10 program. First off should be a powerful V-12 diesel engine (sharing technology with the R10 TDI race engine) packaged to fit in the A8 line.
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