Supercharged direct-inject V6 for new Audi S4

Audi's new S4 and S4 Avant will make their international debut in the city of light when the Paris Salon de l'Auto opens its doors on October 2.

Powered by a supercharged direct-injection V6 displacing 3.0 litres and developing 245kW of power, the A4-based sports sedan and wagon will despatch the 0-100km sprint in V8 times (5.1 seconds for the sedan, 5.2 for the Avant) and yet use a miserly four-cylinder-like quantity of fuel in combined-cycle testing (9.7L/100km for the sedan, 9.9 for the Avant).

At the heart of the S4's performance potential, the supercharger sits compactly between the cylinder banks of the 90-degree V formation engine, where an inlet manifold would be located in a conventional port-injected engine.

Audi engineers opted for a supercharger over a twin-turbocharger application on the basis that the supercharger as one unit could provide the necessary boost (resulting in peak torque of 440Nm, occurring between 2500 and 4850rpm), without 'turbo lag' and within the restrictive packaging constraints. According to the German manufacturer, the supercharger sucks air through the throttle valve, allowing a short path for the airflow to the cylinders, increasing efficiency.

Two four-vane 'rotary pistons' can run at up to 23,000rpm, but will run freely without load, effectively mimicking the high-efficiency operation of turbochargers when not on boost. In addition, the belt-driven supercharger draws air through two integrated charge-air coolers.

Audi labels the V6 engine as the 3.0 TFSI engine, despite the engine being supercharged rather than turbocharged (previously signified by the 'T' in 'TFSI'). The manufacturer now wants people to think of the 'T' as meaning forced induction generally, not just turbocharging specifically. In the case of the S4, the forced induction is an advanced solution for an altogether new engine family, which will also be employed in future Audi models.

Although fitted as standard with a six-speed manual transmission, the new car will also be available with a seven-speed S tronic transmission (Audi's version of Volkswagen's DSG -- but with seven speeds, not six).

In spite of the car's high performance potential, traction is kept in check by Audi's quattro drive system, optionally available with a sports differential for the rear axle.

Audi advises that the S4 models are still about six months away from retailing in Europe and the company won't begin local delivery until the second half of 2009.