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FSI: high-powered petrol direct injection

The name FSI denotes Audi's petrol direct injection technology where, in contrast to the conventional system of injecting fuel into the intake manifold, the fuel is injected directly into the combustion chambers. The superior thermodynamics of this method enhance the engine's overall efficiency.

FSI engines develop more power and dynamism than conventional units with indirect manifold injection – and they do so whilst achieving a very high standard of fuel economy at the same time. By boosting efficiency in this way, Audi has once again demonstrated the brand's proverbial "Vorsprung durch Technik".

In June 2001, Audi's direct petrol injection technology confirmed its tremendous potential in what must be the most challenging endurance test in the world when an FSI power unit propelled the Audi R8 prototype sports car to an impressive overall victory in the Le Mans 24 Hours. This success was followed by numerous further victories over the next four years.

The FSI engines from Audi combine petrol direct injection with a newly developed, demand-controlled single-piston high-pressure pump for each bank of cylinders. This pump feeds exactly the right quantity of fuel into the system to attain the operating pressure of between 30 and 100 bar in the common rail. In the intake tract, which includes the two-stage variable intake manifold, charge motion flaps swirl the air intake to produce a fast, tumbling motion.

In this way a homogeneous fuel-air mixture with a lambda ratio of one is formed in the combustion chambers. Injecting the fuel directly also has the effect of cooling the chambers, thereby reducing the tendency to knock. This gave the development team sufficient scope to raise the basic compression ratio to 12.5:1 in both V engines, compared to a ratio of around 10.5:1 for indirect-injection engines.

The result is a more efficient combustion process resulting in higher power delivery, that translates first and foremost into more spontaneous response. The FSI units demonstrate another of their fortes in the frequently used partial throttle range where they burn less fuel than an indirect-injection engine.

350 bhp: the 4.2 FSI

With a capacity of 4,163 cc, the V8 FSI power unit that is now making its debut in the A6 range is derived from the engine in the Audi Q7 and is also a close relation of the powerplant which can be found under the bonnet of the mighty Audi RS 4. The reduction in the maximum rev speed means that the version in the A6 allroad quattro delivers 257 kW/350 bhp at 6,800 rpm. Torque, on the other hand, is even more abundant than in the RS 4, peaking at 440 Nm at 3,500 rpm. 85 percent of maximum torque is on tap as low down as 2,000 rpm.

The V8 engine's cylinder block is based on a bedplate structure, where all of the crankshaft bearings are held together in a subframe for extra reinforcement. The crankcase is cast from an aluminium/silicon alloy, with the pistons sliding along the hard silicon crystals inside the cylinder liners. There is no need to insert separate liners allowing the use of bore bridges that are just 5.5 mm wide, a low overall weight and an overall length of just 464 mm.

The four camshafts are driven by a low maintenance double-stage chain drive consisting of three simplex roller chains. It is fitted in a space-saving location on the rear face of the engine, reducing the overall length by a whole 52 mm. A fourth chain drives the ancillaries.

The V8 power unit features a two-stage variable intake manifold made of magnesium. Two high-pressure pumps driven by the intake camshafts feed the petrol to two interconnected stainless steel rails. The petrol is then injected directly into the combustion chambers via the injector valves. The entire process is managed by a single control unit from Bosch – the Motronic MED 9.1.1, one of the most sophisticated units on the international market.

The prodigious power reserves of the V8 FSI unit bestow the new Audi A6 allroad quattro with performance on a par with a sports car. The sprint from standstill to 100 km/h is over in a fleeting 6.3 seconds; top speed is limited to 250 km/h. The sublime V8 is available exclusively in conjunction with tiptronic.

Thanks to the super-efficient FSI technology, consumption is just 11.2 litres of Super Plus per 100 km; the V8 will also run on premium unleaded petrol, albeit with a slight loss of power. It goes without saying that the V8 FSI engine meets the EU4 emissions standard. Two close-coupled multi-stage catalytic converters are integrated into the exhaust system in a compact manifold/catalytic converter module. Tubular sheet-metal manifolds with air-gap insulation are designed for extra-fast activation of the catalytic converters, ensuring that exhaust emission control starts as quickly as possible after the engine has been switched on.

Compact lightweight: the 3.2 FSI

The 3.2 FSI boasts all the same credentials of an ultra-modern engine that can be found in the V8. And, just like its larger sibling, it too has been designed for maximum space efficiency. Measuring only 360 mm in length and 430 mm in width, and weighing a mere 169.5 kg thanks to its aluminium construction, the engine offers tangible benefits in terms of handling characteristics. The cylinder bore of 84.5 mm and stroke of 92.8 mm – precisely the same dimensions as on the V8 FSI – add up to an overall engine capacity of 3,123 cc.

Fine-tuning of the exhaust system produces a distinctly sporty, classic V6 sound that is never intrusive however, making the qualities of the engine a truly sensory experience for the driver. The V6 power unit offers instantaneous throttle response and races all the way up to the red line at 7,200 rpm with consummate ease.

The 3.2 FSI delivers its maximum output of 188 kW (255 bhp) at 6,500 rpm; its peak torque of 330 Nm is available at just 3,250 rpm. Over 90 percent of the engine's maximum torque is continuously available across a wide rev range from 2,400 to 5,500 rpm – an unprecedented characteristic for a naturally aspirated V6.

Partnered by the 6-speed manual gearbox, the V6 power unit catapults the A6 allroad quattro to 100 km/h in 7.2 seconds and on to a top speed of 242 km/h. Average fuel consumption is 11.0 litres of premium-grade fuel per 100 km, providing yet further evidence of the capabilities of the FSI technology. The corresponding figures for the 6-speed tiptronic transmission are 7.7 seconds, 240 km/h and also 11.0 litres per 100 km.

TDI: high-tech diesel power

Two V6 diesel engines with displacements of 3.0 and 2.7 litres which made their debut in the A6 will be available for the new A6 allroad quattro, too. The two engines both use four valves per cylinder and are part of Audi's new V-generation line-up. Featuring a chain drive for the camshaft and oil pump, they boast extremely compact dimensions.

The engines measure just 444 mm in length, while the 3.0 TDI unit weighs in at a mere 219 kg, making it one of the lightest diesel engines in its class. This is largely down to the use of an ultra-high-tech material for the cylinder blocks: high-strength vermicular-graphite cast iron.

To ensure an optimum throughput of air, the turbochargers in the two V6 diesel power units work on the principle of variable turbine geometry. Mixture preparation is the task of a latest-generation common-rail system, featuring a high-pressure pump and a rail for each bank of cylinders. The high injection pressure of as much as 1,600 bar results in even finer atomisation of the fuel, meaning superior mixture preparation and more efficient combustion.

Lightweight design close up: the injector needle weighs 4 grams

The piezo inline injectors are undoubtedly the most important innovation of the new common rail system, however. They make use of the piezo effect where an electric voltage is applied to ceramic, altering its crystal structures. The result is a minimal expansion which is transmitted to the injector needle inline. The moving mass at the injector needle has been reduced from 16 to 4 grams. This enables considerably smaller and more precisely metered injection quantities.

The number of injection processes per power stroke can be varied and optimised almost at will thanks to the piezo injectors. Audi's TDI development engineers opted for up to five injection processes for the 3.0 V6: in addition to the main injection process, double pilot injection takes place at the lower end of the engine speed range and single pilot injection at medium engine speeds. On top of this, single post-injection also takes place up to around 2,500 rpm at partial throttle.

This strategy produces both lower emissions and a smoother combustion process, which in turn benefits the engine acoustics significantly – both TDI units offer class-beating smoothness. At the same time, multipoint injection cuts exhaust emissions. Plus, a portion of the exhaust gases are recirculated and reused for the combustion process, having first been cooled, with the express aim of reducing nitrogenous emissions.

450 Nm: the 3.0 TDI

A veritable powerhouse is available for the A6 allroad quattro in the guise of the 3.0 TDI. Delivering 171 kW/233 bhp at 4,000 rpm and 450 Nm, this diesel unit is able to call upon vast reserves of output and torque from its capacity of 2,967 cc. Maximum torque is available from a mere 1,400 rpm, giving the driver phenomenal pulling power throughout the rev range.

For optimum charging of the cylinder under all operating conditions, the engine has a turbocharger which is accommodated inside the "vee" to make the best use of the available space. Two intercoolers running in parallel reduce the temperature of the intake air drastically, further optimising cylinder charging. The high-speed glow plugs in the combustion chambers are designed to operate in extreme cold, heating up to a temperature of 1,000 degrees within the space of just two seconds.

The exhaust gas is purified by a close-coupled preliminary catalytic converter – located close to the turbocharger – and the main underfloor converter. As a result of all these measures, the A6 allroad quattro 3.0 TDI comfortably undercuts the limits imposed by the EU4 emissions standard. As on the 2.7 TDI, a diesel particulate filter is included as standard in Germany.

The Audi A6 allroad quattro 3.0 TDI is available with a choice of a 6-speed manual gearbox and the 6-speed tiptronic transmission. It covers the standard 0 100 km/h sprint in just 7.5 seconds (with tiptronic 7.8 s); top speed is 231 km/h (with tiptronic 230 km/h). The mighty diesel exercises extreme restraint when it comes to its fuel consumption however, requiring just 8.4 litres per 100 km (tiptronic: 8.8 l).

Powerful and economical: the 2.7 TDI

Fun yet economical, refined and ecological: the 2.7 TDI is an extremely gifted all-round talent. It also lists high output and abundant torque amongst its strengths, and combines them with excellent fuel efficiency.

Reducing the stroke by 8.3 mm to 83.1 mm whilst leaving the bore unchanged at 83.0 mm results in an overall swept volume of 2,698 cc. The vital performance statistics read as follows: an output of 132 kW (180 bhp) across an engine speed range of 3,300 to 4,250 rpm and a peak torque of 380 Nm available from just 1,400 rpm all the way up to 3,300 rpm – as far as the driver is concerned, this translates into remarkable power in virtually any situation. The highly refined acoustics are just another of the 2.7 TDI's many virtues.

The time of just 9.3 seconds for the sprint from standstill to 100 km/h testifies to the dynamism of the 2.7-litre diesel model; the fuel consumption figure of 8.7 litres per 100 km bears witness to its fuel efficiency. The 2.7 TDI engine is coupled with the silky smooth 6-speed tiptronic transmission.

A model of precision: the transmission

The manual versions of the new Audi A6 allroad quattro – the 3.2 FSI and the 3.0 TDI – come with the ML generation of transmissions, the initials ML identifying them as "manual/longitudinal". This transmission with its sporty, close ratios offers short, crisp and supremely smooth gearshifts. A special mount for the selector forks effectively isolates the gear lever from driveline vibrations, while a raft of further measures raise overall efficiency by reducing internal friction.

The 6-speed tiptronic automatic transmission is available for all of the engines in the Audi A6 allroad quattro range, and is even fitted as standard on the 2.7 V6 TDI and 4.2 V8 FSI models. This transmission converts the engines' power potential into a matchless blend of dynamic performance and delightful ease of use. Compared with its five-speed predecessor, the new six-speed transmission is 8 kilograms lighter with an overall weight of just 120 kilograms.

Again compared with the previous five-speed automatic transmission, the gear ratio spread has widened by 22 percent. This means sharper acceleration in the lower gears as well as a clear reduction in engine speed, and consequently a reduction in both noise level and fuel consumption, at high speeds.

The tiptronic control bears the name DSP (dynamic shift program). The lightning-fast gear changes and flexible gearshift strategy add sporting flair, as does the double-declutching initiated by the engine management during downshifts. With the selector lever in position D and when the S sport program is engaged, the electronics are programmed to respond to parameters such as lateral and longitudinal acceleration as well as to movement of the accelerator pedal. This helps to prevent any unwanted upshifts when cornering.

Permanently a step ahead: quattro four-wheel drive

The quattro permanent four-wheel drive system, a standard feature common to all of the A6 allroad quattro models, is the very technology that has secured Audi its decisive status as technological leader for over quarter of a century now. quattro transforms the motoring experience, ensuring sure-footed traction and cornering and serving as a solid basis for dynamic handling and an extremely high degree of directional stability in all weathers.

At the heart of the quattro four-wheel drive in the new A6 allroad quattro is once again a self-locking centre differential. Operation of the differential is purely mechanical, meaning response is instantaneous. Its locking action is only prompted when the throttle is open; differences in rotational speed are tolerated when the brakes are applied and when cornering. Power is generally split 50:50 between the front and rear axles but, if necessary, up to 75 per cent of drive torque can be diverted to either axle.

Chassis

The chassis of the new A6 allroad quattro relies on technology which has already proven its sporting prowess: the advanced four-link front suspension so typical of Audi partnered by the self-tracking trapezoidal-link rear suspension adopted from the Audi A6. The main components are made of lightweight aluminium, which reduces the unsprung masses significantly. As on Audi's sporty luxury saloon, the A8, adaptive air suspension makes up part of the standard package on the A6 allroad quattro.

Not only has wheelbase been increased significantly compared with the previous model, the car's track has also widened: by 22 mm at the front to 1,596 mm and by 2 at the rear to 1,587 mm. Weight distribution between the front and rear axles has also been optimised by the development team to ensure that the A6 allroad quattro delivers a dynamic drive of the very highest calibre.

Relocated and lightened: the front suspension

In relation to the passenger cell, the four-link front suspension of the A6 allroad quattro has been moved forward by 83 millimetres compared with the previous model, thus ensuring a far better axle load distribution. Not only that, but the change in proportions looks good too as it makes the front overhang far shorter and thus gives the entire car a much more compact appearance.

Four aluminium transverse links guide each wheel. The axle subframe has a sheet-metal construction, the upper bearing block is made of cast aluminium. In keeping with the lightweight design principle, the anti-roll bar has a hollow design. The entire kinematics and elastokinematics of the suspension have been honed with the express purpose of maximising the vehicle's dynamic handling capabilities and ride comfort. Lateral rigidity in particular has benefited from precision redevelopment of all link bearings. Enlarged rubber mountings on the subframe insulate the cabin from road impacts.

Sporty and comfortable: the steering

The new Audi A6 allroad quattro comes as standard with a hydraulic rack-and-pinion steering system featuring speed-sensitive power assistance – Audi servotronic. There is no end to the talents of the latest, most advanced version of the system. A minimum of effort is required when parking, at higher speeds the steering offers drivers utmost precision and excellent feedback from the road. And, with its high level of sensitivity around the straight-ahead position, the servotronic steering's initial response characteristics are highly reassuring too.

The steering column in the new Audi A6 allroad quattro is adjustable by 50 millimetres in an axial direction and 40 millimetres vertically. Meticulous care has been taken to ensure that vibrations at the steering wheel are suppressed almost entirely.

Safe and dynamic: the rear suspension

One of Audi's technical triumphs is now making its debut in the new A6 allroad quattro – the self-tracking trapezoidal-link rear suspension. Its highly complex, supremely effective construction achieves top-class ride comfort paired with infallible dynamic potential.

The trapezoidal links have a hollow, sand-cast structure made from aluminium. These torsionally rigid, non-flexing links absorb a large portion of the forces acting on the wheels. Together with the track rods located behind them, they thus determine the elastokinematic behaviour of the axle. The track rods have a lightweight sheet steel structure. All wheel location elements pivot at the flexibly mounted subframe by means of rubber-metal mountings. Four large, hydraulically damping mounts help to insulate the body against vibrations.

In terms of kinematics, the trapezoidal-link rear suspension has been purpose-developed for sporting characteristics. The reduction in the change in track width as a function of spring travel improves the straight-line stability, steering precision and handling of the A6 allroad quattro.

The entire construction has been configured to provide neutral handling characteristics with a slight tendency to understeer when the vehicle is pushed to its exceptionally high limits.

Riding on a carpet of air: adaptive air suspension

Adaptive air suspension comes as standard on the new Audi A6 allroad quattro. It creates a perfect synthesis of sporty handling on the one hand and silky ride comfort on the other, adding a further key dimension to the vehicle's roadholding abilities in the process.

The new A6 allroad quattro has air spring struts at the front wheels, with the air bellows arranged concentrically around the infinitely adjustable twin-tube shock absorbers. The air-suspension bellows consist of a special, multi-layered elastomer material with polyamide cord threads to increase strength. The combination of the individual layers helps the new A6 allroad quattro to achieve outstanding ride qualities and respond sensitively to minor jolts.

Occupant comfort is enhanced by one of the inherent features of the air suspension system: the vibration characteristics remain constant at all times, regardless of the load the vehicle is carrying. This is because extra air is pumped into the springs by the compressor when the vehicle is heavily laden and discharged again when the load is removed. On the rear axle, the air springs and regulated shock absorbers are separated from one another. The advantage of this configuration, as with a conventional suspension, is that it allows a large through-loading width in the luggage compartment.

The adaptive air suspension together with all of its components – air bellows and shock absorbers included – is controlled electronically; to a large extent, its control characteristics adjust automatically depending on the type of road surface and driving style. Drivers of the A6 allroad quattro also have the option of altering the body's ride height manually by up to 60 millimetres using the MMI terminal. There is a choice of five driving modes in all known as dynamic, automatic, comfort, allroad and lift.

In dynamic mode, which is the equivalent of a sports suspension, the body drops to leave 125 mm of ground clearance. This makes for even more agile handling, in addition to reducing drag and consequently fuel consumption. In automatic mode, the body is positioned 15 mm higher, but drops down to the dynamic level when the vehicle is driven for prolonged periods at over 120 km/h. If the comfort mode has been selected, the body is not lowered in this way.

The allroad mode provides a ground clearance of 175 mm; the body is lowered by 15 mm when the speed reaches 80 km/h and by a further 20 mm at 120 km/h. In the manually selected lift mode, the body hovers 185 mm above the ground to negotiate rough terrain at slow speeds – a whole 65 mm more than on the A6 Avant.

Should a speed of 35 km/h be exceeded, the control unit automatically switches to the allroad mode. Consequently, the A6 allroad quattro is perfectly at home on all roads and tracks.

Keeping a firm grip on things: the braking system

The new Audi A6 allroad quattro comes with a powerful braking system to harness the potential of its engines. Even the entry-level engines are paired with 16-inch brakes, and the mighty 4.2 FSI features a 17-inch system. The front brake discs measure 321 millimetres in diameter and 347 mm on the 4.2 FSI. The rear brake discs have a diameter of 302 mm (4.2 FSI: 330 mm with internally ventilated discs).

The system is operated via a dual-rate booster. At light to moderate rates of deceleration, it boosts the pedal force by a factor of 5.5, allowing for sensitive control of brake power. Above a predefined threshold, the boost factor is raised to 12, meaning a disproportionate increase in the rate of deceleration in relation to the force applied at the brake pedal – a clear asset for drivers preferring a particularly sporty style of driving. In the event of an emergency stop, the hazard warning lights come on automatically.