New Audi A8 4.2 TDI quattro

Press Release

World's highest horsepower V8 diesel-engined car

240 kW (326 bhp): With this extremely impressive horsepower output, the new Audi A8 4.2 TDI quattro puts itself ahead of all the other diesel-engined cars on the international market. The entirely redeveloped 4.2-litre, eight-cylinder biturbo engine accelerates the lightweight saloon with its aluminium body from 0 to 100 km/h (0 – 62 mph) in just 5.9 seconds. The top speed is electronically restricted to 250 km/h. In addition to these dynamic qualities, the new power plant displays the kind of refinement that sets standards even in the top segment of the motoring world, and ennobles the A8 4.2 TDI quattro, turning it into the perfect long-distance touring saloon.

The new engine is also exemplary in terms of economy. Combined as standard with quattro permanent four-wheel drive and 6-speed tiptronic transmission, it uses on average just 9.4 litres of diesel fuel for every 100 kilometres. This means it will cover more than 950 kilometres (590 miles) on a full tank without a stop.

The Audi A8 4.2 TDI quattro is equipped as standard with a diesel particulate filter, which works without additives and consequently lasts the lifetime of the vehicle without servicing.

The A8 4.2 quattro has a chassis with air suspension and adaptive damping – otherwise known as Audi adaptive air suspension. It allows the vehicle to be driven either in a decidedly sporty fashion or with an extremely comfortable ride, just as the driver wishes.

Like the other A8 models, the new TDI has the exclusive front end with single-frame radiator grille. The luxury saloon can be ordered from beginning of June either with the standard wheelbase or in its long-wheelbase version, which is 130 millimetres longer. First deliveries will take place in the third quarter of 2005. The basic price of the A8 4.2 TDI quattro in Germany is € 81.000.

The sheer power and the characteristics of this eight-cylinder power unit once again reaffirm the credentials of the Audi A8 as the sportiest saloon car in the luxury segment. And thanks to its top-of-the-range TDI, Audi yet again demonstrates its expertise and its lead in the development of such powerful, refined and, not least, economical diesel engines.

Entirely redesigned engine

The predecessor of the new A8 4.2 TDI had already scored top marks among the luxury-class diesel saloons with its 4-litre, eight-cylinder engine. Thanks to its 275 bhp and 650 Nm of torque, it was the most powerful V8 diesel-engined car for a long period following its debut in the summer of 2003. Its fuel consumption figures of just 9.6 litres per 100 km also earned it a top place among its competitors. With these features the A8 4.0 TDI succeeded in becoming the European number one among the V8 diesel luxury saloons, with a market share of 71 %.

In the light of such statistics, the development goals for the new TDI represented a daunting challenge:

-          The most powerful car diesel engine on the market.

-          Top figures in terms of driving dynamics, with low fuel consumption

-          Optimum engine acoustics

-          Low weight

-          Compact, short design

In order to implement these specifications, Audi's TDI development team designed an entirely new engine. Just like the 3.0 and 2.7 TDI before it, the 4.2-litre V8 TDI is a member of Audi's new family of V-format engines, and has chain-drive for the camshaft and ancillaries.

The cylinder spacing in the new engine block is now 90 millimetres. This gives the engine a compact overall length of just 520 millimetres. One current competitor V8 with the same engine capacity measures all of 140 millimetres more.

The engine block weighing 62 kg altogether is made of vermicular graphite cast iron (GGV) – an important factor in achieving the low engine weight of only 255 kilograms. This is 15 kilograms less than its predecessor, the 4.0 TDI.

The 4.2 TDI is thus one of the lightest V8 diesels ever. This benefits the power-to-weight ratio and the weight distribution in equal measure – two characteristics that are of central importance for the driving dynamics of the new A8 4.2 TDI quattro.

With an engine capacity of 4,134 cc, the combustion chambers of the new engine are almost exactly 0.2 litres bigger than in the case of the 4.0 TDI. The bore has been enlarged by 2 mm compared with its predecessor, to 83 millimetres, and the stroke of 95.5 millimetres is identical with that of the 4.0 TDI. The compression ratio is 16.5 : 1.

The surfaces of the cylinder bores are treated using UV laser exposure. This special honing process ensures significantly reduced oil consumption in the TDI engine, and, as a result, a significant reduction in particulate formation during combustion.

The forged crankshaft made of chrome molybdenum steel is offset in such a way that forces and moments of the first and second order are avoided – a decisive bonus delivering extremely low levels of vibration.

Chain drive for camshaft and ancillaries

The cylinder head is made of aluminium, and two camshafts are used to operate the valves in each. They are driven via a maintenance-free chain drive, which also drives the oil, water and power-assisted steering pumps.

There are four valves per cylinder, for optimum charging of the combustion chamber. The valves on the new V8 are operated by roller cam followers with hydraulic valve clearance compensation. This low-friction drive technique plays a decisive part in reducing both the fuel consumption and the emissions of the 4.2-litre engine.

The use of roller cam followers is likewise beneficial to the engine's acoustics. In conjunction with the twisted-type and therefore virtually play-free camshaft drive, these followers are instrumental to the reduction in mechanical noise from the valve gear and contribute to the 4.2 TDI's outstandingly quiet running.

The rigid construction of the engine block and the unit’s effective encapsulation also help to lessen the sound emitted by the eight-cylinder engine.

Biturbo with two intercoolers

A concept that has already proven its worth on the 4.0 TDI engine. Two turbochargers with variable turbine geometry deliver high torque even at low engine speeds, in conjunction with high power output. Variable turbine geometry means that the flow of exhaust gas to the turbine rotor can be optimised depending on load and engine speed. By means of air mass metering, the engine management ensures that both turbochargers run constantly at the same speed and therefore achieve the same delivery rate. Maximum boost pressure is 2.5 bar; the turbochargers rotate at up to 226,000 revolutions per minute.

The variable turbine geometry is supported by electrically operated actuators on the new 4.2 TDI. These actuators adjust the vanes faster and more precisely: particularly at low engine speeds, this means a more rapid build-up of boost pressure, thus achieving an excellent response.

The 4.2 TDI has two intercoolers, arranged on the right and left in front of the engine. They are ideally positioned in the airflow beneath the headlights, and are therefore capable of operating extremely efficiently.

Each of the two turbochargers serves one bank of cylinders. The two intake manifolds are interconnected by means of a "feedthrough" system, to equalise the pressure between the right and left cylinder banks. This feature boosts cylinder charging and consequently enhances the engine's output.

There are continuously variable swirl flaps integrated into the intake tract. These permit the air movement to be adjusted to suit the engine speed and load at the time. High tumble at low engine load results in optimised combustion, just as low tumble does at high engine load. In practice this means that a closed swirl duct at low load increases swirl, while open ducts at high load boost cylinder charging.