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Audi AG is returning to its roots, in more than just the figurative sense, as it unveils a new premium 3.0L DOHC V-6 fitted with a supercharger and direct-gasoline injection.
Expected to be offered in the all-new ’09 S4 sport sedan (replacing the previous model’s thirsty 4.2L V-8), as well as the midsize A6 range when it goes into production later this year, the new engine produces 290 hp at nearly 5,000 rpm and 310 lb.-ft. (410 Nm) of torque between 2,500 rpm and 4,850 rpm.
Although labeled a TFSI (Turbocharged Fuel Straight Injection) mill, similar to the auto maker’s Ward’s 10 Best Engines-winning 2.0L turbo-4, Audi says the “T” no longer exclusively designates turbocharging as a means of forced induction.
The 4-ring brand is no stranger to belt-driven superchargers, as its Grand Prix racers built by Auto Union in the 1930s employed compressors to yield as much as 600 hp from their 12- and 16-cyl. engines.
Audi says the decision to return to the technology, rather than designing a twin-turbo setup for the new V-6, stems from packaging and throttle-response advantages brought by the roots-type supercharger’s layout.
The unit takes the place of the intake manifold and nestles between the engine’s 90-degree cylinder banks.
Belt-driven off the crankshaft that can spin up to 6,500 rpm, the mechanical compressor’s 4-lobe rotors can generate nearly 12 psi (0.8 bar) at speeds approaching 23,000 rpm.
Combined with a new DGI system, which features common-rail fueling and 6-hole injectors capable of three injections per cycle, the result is a compact and efficient powerplant with solid low-revving responsiveness, Audi says.
Twin water-to-air intercoolers, connected by a separate cooling circuit, chill the incoming air for better combustion, while acoustic management keeps the supercharger’s inherent whine to a minimum.
Other highlights include tumble flaps in the intake ports for optimal fuel-air mixing, as well as a total package weight of 417 lbs. (189 kg).
Although the 3.0L TFSI V-6 has a lofty 10.5:1 compression ratio, the auto maker says it can operate on either regular or premium gasoline, while also meeting Euro 5 emissions limits.
In addition, the low-end power allows the engine to be paired with taller, more-efficient transmission ratios, with fuel consumption in vehicles sporting longitudinal drivetrains averaging at least 24 mpg (10 L/100 km) in the European cycle.
