Audi has a long history of using five-cylinder engines in its vehicles, from the unit that was integrated in to the Audi 100 5E in 1977 to the 1995 Audi RS2 with an engine that produced 232kW.
And while many vehicles that may have used five-cylinder technology instead adopted V6 units, as pressure to downsize and meet performance and efficiency targets became more challenging a comeback followed in 2009 with Audi TT RS. The turbocharged, direct-injection transverse engine produced 250kW of power from its 2.5 litre displacement, then in 2013 this figure went up to 265kW.
Now the output levels have been taken a step further with the latest generation of the two seater sports car, with its five-cylinder engine producing 294kW.
That makes the five-cylinder 17% more powerful with maximum torque of 480Nm available from 1,700rpm to 5,850rpm helping the Audi TT RS coupe to accelerate to 100km/h in 3.7 seconds. The Roadster takes 3.9 seconds.
Audi said: “At less than 500mm in length, the 2.5 litre engine is compact and is 26kg lighter than the previous model. Its crankcase is made of aluminium, which alone saves 18kg.”
The unit’s cylinder barrels are plasma-coated and the crankshaft main bearings are 6mm smaller in diameter. The crankshaft is hollow bored and is 1kg lighter according to the OEM while the aluminum pistons integrate channels for the oil cooling. In the short warm-up phase after a cold start, the switchable water pump doesn’t circulate coolant in the cylinder head. This lowers the coefficient of friction and reduces fuel consumption.
“The gas exchange of the five-cylinder engine is designed for high throughput. The large turbocharger forces the intake air into the combustion chambers at up to 1.35bar. The intercooler with its efficiency level of 80% reduces the temperature for the highest possible oxygen percentage. Intake and exhaust camshafts can be adjusted as required,” said Audi.
To achieve a better mixture preparation, the 2.5 five-cylinder engine works with a dual injection system. It provides the option of injecting fuel into the intake manifold as well as directly into the combustion chamber. The duration and type of injection can be varied for each engine operating point depending on the driver’s needs.
But it is the noise of the five-cylinder unit that many consumers will be most interested in as it is part of the pleasure of driving a high-performance sports car.
“The engine has a firing interval of 144º and because of the 1-2-4-5-3 ignition sequence, ignition alternates between adjacent cylinders and those far apart from one another. This delivers a special rhythm and character. The uneven number of cylinders results in harmonic frequencies that accompany the basic tone,” said Audi.
To add to the acoustic behaviour at higher throttle, the flaps in the exhaust system open, and there is a sound button on the centre console – something that is also present on the V10-engined R8.
But while vehicles such as the TT RS might be developed for a purer, more engaging drive, efficiency still has to be considered which is why the TT RS has stop-start and a recuperation system. Because of this it consumes 0.3 litres less fuel in the NEDC test cycle than its predecessor. The coupé consumes 8.2 litres/100km which corresponds to CO2 emissions of 187g/km. The Roadster consumes on average 8.3 litres and emits 189g/km.
|tags:||Audi High Performance|