Exhaust System - Audi TT RS Service Training

Exhaust system

When the car is accelerated at full throttle, the typical sound of
the five-cylinder engine is delightfully resonant in the intake and
exhaust system. And yet the sound is unobtrusive when driving at a
constant speed and under moderate acceleration.
To ensure compliance with the EU-5 exhaust emission standard, it
was necessary to position the pre-catalyst as close as possible to
the turbine outlet. The catalytic converter is made of a ceramic
material. The continuous-duty oxygen sensor, which is integrated
directly in the exhaust turbocharger module, is also positioned at
the turbine outlet. The post-cat oxygen sensor is located directly
downstream of the pre-catalyst and has a non-linear characteristic.
Pre-catalyst
Exhaust flap
The exhaust gases are admitted into the large rear silencer behind
the two centre silencers. The rear silencer, in turn, has twin tail-
pipes.
The left tailpipe is fitted with an exhaust flap. When this flap
opens, the sound becomes even more sporty. The exhaust flap is
opened and closed by a vacuum cell. For this purpose, the exhaust
flap 1 valve 1 N321 is activated by the engine control unit.
If the Sport button is pressed at idle and when the vehicle is at a
standstill, the exhaust flap opens, thus allowing the system to be
checked quickly and easily. The opening and closing of the exhaust
flap are otherwise computed by a map in the engine control unit.
If the exhaust flap 1 valve 1 N321 fails or if a leakage occurs in the
hose system, the exhaust flap stays continuously open.
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Isolating elements
Underbody catalytic converters
The two underbody catalytic converters are positioned further
down the exhaust system, which has a twin-flow configuration
after the pre-catalyst. Both catalytic converters are of metal con-
struction.
A further focal point in the development of the exhaust system
was minimising exhaust gas backpressure. Hence, the exhaust
pipes are very large and, in part, have a twin-flow configuration.
A sport exhaust system with black tailpipe trims is available as an
option, in addition to the basic exhaust system. It has an even
more distinctive soundscape.
Centre silencer
Vacuum cell
Rear silencer
Tailpipe trims
451_052
451_071