Audi R8 V12 TDI: Exotic Diesel

Motoring Channel Staff - 14/January/2008

Detroit, America — The debate raging around the new Audi R8 V12 TDI is not whether it will be able to out pace Italian exotica - it will - but whether it will sound good while doing it.

In place of the 4.2-litre petrol V8, Audi has dumped a 6.0-litre V12 twin turbocharged diesel engine into the mid-mounted engine bay of the R8, and the results are mind numbing.

But the exhaust note and may be somewhat agricultural, more clang than pitch perfect fang. Even so, it was still one of the most anticipated launches at the 2008 Detroit Motor Show.

According to Audi however, "Its sound is as thrilling as you'd expect in a sports car of this calibre. For all the subtle smoothness that typifies this design principle, the 12-cylinder unit is full-bodied and equipped with energetic overtones that make no secret of its performance potential."

The zero to 100km/h sprint takes just 4.2 seconds in the Audi R8 V12 TDI, which puts this diesel-engined sports car in the realm of the Lamborghini Gallardo and Ferrari F430.

Audi's normal R8 model hits 100km/h from standstill in 4.6 seconds, making the diesel version's  standing starts almost half a second quicker.

Mated to a 6-speed manual transmission, it has a top speed of more than 300km/h (186mph) and makes peak torque of 1000Nm @ 1750rpm. This huge amount of torque is made possible thanks to the insane amount of pressure delivered by the twin turbos, peaking at 37.7psi (2.6 bar).

Maximum power is a stomach-churning 368kW (500 metric horsepower) and while offensively powerful, the engine is a friend of the environment with Euro 6 compliancy, which isn't expected to come into effect until 2014.

The normal petrol version of the Audi R8 has been an instant hit with buyers despite it's eye-watering price, with virtually no stock left for the rest of 2008. 

With this in mind, the Audi R8 V12 TDI would probably sell many units for the German company, though Audi has not yet green-lit the project. The vehicle on display is a 'concept' as far as Audi is concerned, but if the demand is there, and the business case is strong expect this fire-breathing, oil-burning sports car to be on sale in 18 months.

To the casual observer the new R8 V12 TDI would appear no different than the production V8 version, but there are subtle visual changes.

The glass roof is one, joined to a different engine cover, as is the car's wider stance and slightly larger rear-mounted air intakes that provide the 6.0-litre engine with more oxygen for better aspiration.

Up front the car has a slightly difference 'face' with trios of minute air inlets below the LED headlight lenses. Below there are intersecting pairs of horizontal fins that add even more aggression to the vehicle's front end. 

New 5-spoke alloy wheels are one of the clearest clues as the vehicle's non conformist powerplant, while LED brake lights are also new.

With a highly rigid bodyshell and more power than a military-grade armoured personnel carrier, the Audi R8 V12 TDI concept is also a driver's dream.

Audi says the the precision chassis of the R8 V12 TDI concept remains supremely in control of the sporty engine performance, but is capable of assuring relaxed driving pleasure over long distances too. 

The suspension, with double wishbones at both the front and rear, is optimised for a neutral self-steering response and maximum ease of control, says Audi. The dampening technology known as Audi magnetic ride is also part of the concept car package.

Braking is taken care of by carbon fibre reinforced ceramic discs brakes, whose cores are "frictionally resistant silicon carbide" with a "diamond-like crystalline structure" that are embedded in high-strength carbon fibres. The braking system is cooled by the "intricate geometry of cooling ducts in the ventilated discs" and the large ceramic discs are worked by 6-piston calipers at all four corners.

Built for race track performance, the brakes have a high abrasion resistance that Audi says will permit an operating life of up to 300,000 kilometres (186,411 miles).

V12 Engine: The V12 TDI crankcase is made from gray cast iron with vermicular graphite – a high-tech material referred to as GJV-450 that is already used on the V6 and V8 TDI engines. GJV-450, made by a patented casting process, is about 40 percent more rigid and 100 percent more fatigue-resistant than gray cast iron. This enabled the developers to make its walls thinner, cutting its weight by around 15 percent compared with conventional gray cast iron.

The two cylinder heads are each made from three main elements. These are a base section made from a high-strength aluminum alloy incorporating the intake and exhaust ports, an oil-bearing upper section, and a reinforcing ladder frame supporting the two camshafts.

The valves are actuated by low-friction roller cam followers; the compression ratio is 16.0:1. Map-controlled swirl variation of the combustion air has been adopted from the V6 and V8 TDI engines. This produces permanently optimized swirl concerning both emissions and high performance.

As is the case in the Audi V engines, the no-maintenance chain drive is mounted at the back of the engine, where it occupies little space. Its layout has changed on the new V12 TDI. The camshafts' sprocket engages in an intermediate gear via which two Simplex chains drive the camshafts. Two more chains drive the oil pump and the two high-pressure pumps actuate the common rail injection system.

The two turbochargers are located on the outside of the engine's V, each of them supplying one bank of cylinders. Thanks to their variable turbine geometry, the full flow of exhaust gas always passes through the turbine, so the chargers respond slickly – even at low engine speeds – and operate very efficiently.

The two turbochargers, which generate up to 2.6 bar (37.7psi) of boost pressure, play a crucial role in producing the huge torque of 1,000Nm (737.56 lb-ft) that the V12 TDI maintains from 1,750 rpm to 3,000 rpm. In developing 368kW (500 hp), the diesel achieves a specific output of 62kW (84.3 hp) per litre of displacement.

Two large intercoolers reduce the temperature of the compressed air. The V12 has a twin-pipe exhaust system with two particulate filters. The intake system is similar in structure with one air cleaner per cylinder bank, with an airflow meter behind it. Two control units, sharing the workload in a master/slave principle, manage events in the engine.

The Audi R8 V12 TDI concept already fulfills the Euro 6 emissions standard that is likely to take effect in 2014 and calls for sharply reduced nitrogen oxides. By also designing in ultra-precise fuel metering by the common rail system, Audi's engineers have made full use of current clean diesel technology.

The dynamic character of a sports car depends not just on its performance and torque; the transmission ratios have to be right too. In keeping with the character of a high-performance sports car with unbeatable torque potential, the transmission in the R8 V12 TDI has six manually operated gears.

The manual transmission is very compact in design. Together with the small-diameter double-plate clutch, this means it can be installed low down. The manual transmission has very short shift travel and utterly precise guiding of the shifter into the open gear lever gate. It is made from polished aluminum, has an agreeable feel and exquisite sports car looks.

Such a high-performance Audi also has quattro permanent all-wheel drive. In the case of this mid-engine sports car, power is distributed variably between the front and rear wheels from a starting ratio of 40:60 to optimize the handling.

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