1999 Audi S4 Pictures, Specifications, Information

The sporting and elegant Audi S4 effortlessly makes its mark. A glance at the performance figures for the 2.7-litre V6 biturbo engine with its two small turbochargers that cut in smoothly when needed is enough to show what a superior impression the S4 is capable of making.

Using smaller turbochargers but fitting one to each bank of cylinders has clear advantages on the V6 engine. The more rapid response of the smaller turbines leads to the desired high torque even at low engine speeds. Thanks to their lower inertia, the engine responds more readily to rapid pressure on the accelerator. The short distances between the cylinder exhaust ports and the turbocharger inlets mean that the exhaust gas loses less momentum and charging efficiency is thus increased.

Each bank of cylinders has an intercooler which reduces the temperature of the intake air. Efficient cooling of the charge air is crucial to the forced aspiration principle: the cooler the air, the higher its density and the more oxygen is available for combustion. With cooled air, therefore, it is possible to achieve even higher engine efficiency.

The special shape of the inlet ports, which creates a tumbling motion in the mixture charge as it enters the combustion chamber, also helps to make combustion cleaner and more efficient. The optimum swirl imparted to the fuel-air mixture by this tumble effect improves the combustion process and thus has a positive effect on engine efficiency. The intake camshafts for the two five-valve cylinder heads are hydraulically adjustable to optimise the torque curve. These adjustments to the valve timing increase torque by about ten percent in the low and medium engine-speed ranges.

The power of the V6 twin turbo is converted reliably and effectively into traction by the 6-speed sports-ratio gearbox and permanent four-wheel drive. The S4's aluminium suspension has a noticeably positive effect on handling. In addition to all control arms in the four-link front and double-wishbone rear suspension, all pivot bearings are now made of aluminium as well.

The brake system has also been upgraded to match this surging forward thrust: large ventilated disc brakes front and rear with aluminium brake calipers ensure optimum braking performance.

On the Audi S4, the anti-lock brake system (ABS) and electronic brake-force distribution system (EBD) are under the overall control of the electronic stability program (ESP). This makes the S4 one of the safest high-performance cars on the road.