First drive: A8 V8 TDI is... Diesel Maximus!

IT IS a generally held maxim that high-end luxury cars are the exclusive domain of petrol engines with at least eight cylinders, right? Well, Audi has rewritten the rulebook on accepted thinking, launching a bold attack on the luxury-car segment by introducing a twin-turbo common-rail turbo-diesel engine into its range-topping A8 sedan. The addition of the 4.2 V8 TDI brings to six the number of A8 models, which start from $169,950 for the 3.7-litre quattro.

By adding a TDI, Audi has beaten Mercedes-Benz, which is planning a 173kW/540Nm turbo-diesel S-class later this year, and Jaguar, which is trialling an XJ sedan locally to test buyer reaction.

BMW has said it is unlikely to introduce a turbo-diesel 7 Series – at least until it gauges how successful its rivals are.

Audi also remains the only Euro importer to offer all-wheel drive in its limousine line-up.

Priced from $210,000, the A8 TDI boasts sportscar-like performance from its 4.2-litre twin-turbo TDI V8, which develops 240kW at 3750rpm and 650Nm from 1600rpm.

The beefy diesel endows the car with a 0-100km/h sprint time of 5.9 seconds and a top speed governed to 250km/h. Average fuel consumption is 9.7L/100km combined, giving the limousine a claimed touring range of 950km from its 90-litre fuel tank.

In keeping with Audi’s technology edge, the 4.2 TDI benefits from the latest diesel technology and is paired with a six-speed Tiptronic automatic with a dynamic gearshift program and additional sports program, as well as quattro all-wheel drive.

Its compact V8 has the latest-generation common-rail technology with piezoinjectors, variable turbine geometry, twin intercoolers and twin exhausts with particulate filter. The particulate filter reduces harmful emissions and diesel smoke and is designed to last the lifetime of the vehicle without servicing.

The 4.2-litre TDI V8’s twin variable geometry turbos each serve one bank of cylinders and have a maximum boost pressure of 2.5bar. They are designed to deliver high torque even at low engine speeds, with no turbo lag.

The engine itself is the latest in Audi’s "V" design with aluminium cylinder-heads and four valves per cylinder. The engine block itself weighs 62kg and is made of vermicular graphite cast-iron, which helps achieve an overall engine weight of 255kg, 15kg less than its predecessor, the 4.0 TDI, which was not sold here.

Like Audi’s V6 engines, the V8 adopts chain drive for the camshafts andancillaries. As with all A8 models, the TDI benefits from an advanced aluminium space frame that helps keep weight down to 1945kg and, visually, there is little other than badging to distinguish the car from its petrol siblings.

The limousine shares a four-link front suspension and self-tracking trapezoidal-link rear suspension. It also has adaptive air suspension with continuous damper control and four settings ranging from comfort and dynamic.

Equipment levels mirror the 4.2 petrol V8. This includes adaptive Xenon headlights, 19-inch alloy wheels, dual front, side and curtain airbags, ABS with brake assist, ESP, alarm, sonar front and rear parking, front and rear foglights, LED rear lights, sunroof, a full-size spare wheel, keyless start, six-disc eight-speaker CD stereo and cruise control.

It also has Valcona leather upholstery, multi-media interface/navigation/TV with colour monitor, a height- and reach-adjustable steering, an automatic closing bootlid, multi-function sports steering wheel and electric front seats with electric seatbelt adjustment.

2006 Audi A8 pricing:
A8 3.2 FSI (a) - $159,000
A8 3.7 quattro (a) - $169,950
A8 4.2 quattro (a) - $203,000
A8 4.2 TDI quattro (a) - $210,000
A8L 4.2 quattro (a) - $218,100
A8L 6.0 W12 quattro (a) - $326,000