IT is generally held maxim that high-end luxury cars are the exclusive domain of petrol V8s and V12s, right?

Well, Audi has re-written the rule book on accepted thinking, launching a bold attack on luxury car segment by introducing a twin-turbo common-rail diesel into its range-topping A8 lineup.

The addition of a 4.2-litre V8 TDI brings to six the number of A8 models, which start at $169,950 for the 3.7-litre quattro.

By adding a TDI to the lineup, 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 gauge buyer reaction. BMW has said it is unlikely to add a turbo-diesel 7 Series.

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

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

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

In keeping with Audi’s technology edge, the 4.2 TDI benefits from the very latest in diesel technology, mated to a six-speed tiptronic automatic with 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 piezo injectors, variable turbine geometry, twin intercoolers and twin exhausts with particulate filter.

The particulate filter reduces harmful emissions and diesel smoke and lasts 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 2.5 bar.

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 and ancillaries.

Like its siblings the TDI has an advanced aluminium space frame that helps keep weight down to 1945kg and visually there’s little to distinguish the car from its petrol siblings apart from badging.

The TDI’s also features the same single-frame radiator grille that cuts through the bumper.

It also shares a four-link front suspension and self-tracking trapezoidal-link rear suspension.

The limousine also has adaptive air suspension with continuous damper control and four settings ranging from comfort and dynamic.

The TDI has the same equipment levels as the 4.2 petrol V8.

This includes adaptive Xenon headlights, 19-inch alloys, 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, full-size spare wheel, keyless start, six-disc eight-speaker CD stereo, cruise control, front and rear armrests, Valcona leather upholstery, multi-media interface/navigation/TV with colour monitor, height and reach adjustable steering, automatic closing bootlid, multi-function sports steering wheel, electric front seats with electric seatbelt adjustment.

As well, the TDI has side lighting that operates at the turn of the steering wheel and when reversing.