Audi. Saturday , November 04th , 2017 - 12:39:00 PM
In the induction tract, the intake valves close well before the piston reaches bottom dead center. This very short opening time keeps the fresh gas flow comparatively small. When the piston moves back up again after reaching bottom dead center, the compression phase starts later than usual. This allows a high geometric compression ratio of 10.0:1 - the combustion then takes place in a relatively small volume. In comparison to the short compression phase, the expansion phase is extended, which results in a high level of efficiency.
In the classic Miller cycle, the reduced cylinder charge is detrimental to torque and power output. These aspects have been neutralized by Audi thanks to the implementation of turbocharging and the two-stage Audi valvelift system (AVS). The four camshafts of the 2.9 TFSI can each be adjusted by 50 degrees crank angle. At higher load and engine speed ranges, AVS closes the inlet valve later. The opening time increases from 130 to 200 degrees crankshaft angle, while at the same time the valve lift increases from 6.0 to 10.0 millimeters (0.2 to 0.4 in). Cylinder charging also increases considerably - the 2.9 TFSI revs up powerfully and delivers an impressive output.
With the newly developed 2.9 TFSI, Audi has drawn upon the legendary 2.7 liter V6 from the first RS4 Avant. Produced between 1999 and 2001, it delivered 280 kW (380 hp). Just like the 2.7 liter engine, the new high-performance V6 is also designed as a bi-turbo engine. In comparison with its direct predecessor, a freely-aspirated, high-revving V8 unit, its pulling power and efficiency attain a whole other dimension.
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