Turbocharged gasoline engines are a traditional Audi domain, and the five-cylinder turbo in the Audi TT RS is a high-performance engine. With a displacement of 2,480 cubic centimeters, it produces 250 kW (340 hp) between 5,400 and 6,500 rpm. Peak torque of 450 Nm (332 lb-ft) is already available at 1,600 rpm and remains constant up to 5,300 rpm.
The basic concept makes an Audi five-cylinder unit an unusual engine. It has a firing interval of 144 degrees and a firing order of 1-2-4-5-3, alternately between directly adjacent cylinders and cylinders that are far apart. This produces the distinctive rhythm and musical sound, which are also the result of the intake and exhaust geometry. A specially designed torsional vibration damper at the front end of the crankshaft compensates for the free moments of the engine.
The 2.5-liter TFSI is extremely compact. Its cylinder spacing measures 88 millimeters (3.5 in); the external main bearings were moved inside. Only 494 millimeters (19.5 in) long, the long-stroke engine (bore x stroke 82.5 x 92.8 millimeters (3.3 x 3.7 in)) is suitable for transverse installation in the TT RS.
Its low weight of only 183 kilograms (403.45 lb) is also a top figure. It helps keep the total weight of the TT RS low and also offers significant advantages for the distribution of axle loads and thus for the car’s handling.
The crankcase is made of vermicular graphite cast iron. This high-tech material that made its name in the large TDI engines combines the ultimate in rigidity with low weight. Audi is the first automaker to use this material for a gasoline engine. Targeted reinforcements on the main bearing seat and the main bearing cover further increase the load-bearing capacity of the block.
The pistons are made of cast aluminum; each of them together with the rings and pins weighs only 492 grams (1.1 lb). Just like the forged connecting rods, they are designed to withstand the highest of loads; systematically minimized asymmetries and slightly angled box walls enhance their strength. Sodium-cooled exhaust valves and hardened valve seat rings are used in the cylinder head, which is cast from a high hot-strength aluminum alloy.
TFSI – the winning technology from Le Mans
The powerful five-cylinder engine is surprisingly frugal, requiring an average of just 9.2 liters/100 km (25.57 US mpg) in the Coupé (Roadster: 9.5 l/100 km (24.76 US mpg)). Its high efficiency can be attributed to the combination of FSI direct fuel injection and turbocharging, two of Audi’s core technologies. This TFSI pairing harmonizes perfectly in motorsports, the world’s most demanding test ground: It has powered the R8 race car to five victories in the 24 Hours of Le Mans and 63 victories in 80 other races.
Loads are measured for the injection unit’s controller by means of a pressure sensor in the intake manifold – a particularly precise method of measurement. Pneumatically actuated flaps generate a controlled rotation of the inflowing air in the combustion chamber. The common rail unit injects the gasoline into this roller-shaped “tumble” at a pressure of 120 bar. The fuel is intensely swirled in the combustion chamber and cools the walls, solving a long-standing problem of turbo technology: the risk of knock during combustion. TFSI technology enables a high 10.0:1 compression ratio and correspondingly good efficiency.
The two camshafts also do their part to ensure that the combustion chamber is well filled: They can be hydraulically moved through 42 degrees of crankshaft rotation. They are driven by a two-stage chain drive comprising a particularly quiet sprocket chain, a roller chain and an intermediate timing gear.
The turbocharger is large, with its compressor wheel measuring 64 millimeters in diameter at the outlet. It can theoretically compress 335 liters (11.83 cu ft) of air at full load; the relative boost pressure can be up to 1.2 bar. The turbocharger casing has a separate oil supply and a cooling system serviced by a separate water pump. At full load, the intercooler reduces the temperature of the compressed air and achieves an efficiency of more than 80 percent. The entire admission tract has been optimized for minimal pressure loss and the development engineers succeeded in reducing the exhaust backpressure in the dual exhaust tract.
There is a flap in the left tailpipe. When it is closed, the exhaust is rerouted through the rear muffler and exits through the right tailpipe. The flap opens when accelerating at higher loads and engine speeds. The exhaust now takes the direct route to the outside, producing a fuller, more intense sound.
The driver can open and close the flap as desired by pressing the standard Sport button on the center tunnel, which also makes the engine response more direct or more comfortable. Audi also offers an optional sports exhaust system with black tailpipe trim, including the sound flap, for an even more distinctive sound.
The equipment, specifications and prices stated herein refer to the model line offered for sale in Germany. Subject to change without notice; errors and omissions excepted.