Component Description - Ford Focus RS 2016 Technical Service Training

Lesson 3 – Powertrain
6 Exhaust cylinder 2
7 Exhaust cylinder 3
Unlike a traditional mono-scroll turbo, a twin-scroll
turbo has two separate chambers in the turbo housing
along with two separate exhaust runners that flow into
the turbo, one runner for cylinders 1 and 4 and another
runner for cylinders 2 and 3. Since the cylinders fire in
sequence (not all at once), the exhaust exits the
combustion chamber in irregular pulses.
E203664
1 Compressor wheel
2 Twin scrolls
The Focus RS twin scroll turbocharger is equipped with
a new turbine and larger compressor wheel (60 mm to
63 mm). This permits a higher boost pressure and
ensures improved airflow.
The engine also has an overboost feature increasing
boost above its normal max boost pressure to allow
temporary torque delivery. This feature widens the RPM
range of the peak torque curve, giving maximum
performance while passing another vehicle or launching
from a standing start.

Component Description

Service Training
4
3
2
8 Exhaust cylinder 4
9 Turbine housing exhaust outlet
Conventional mono-scroll turbochargers route those
irregular pulses of exhaust into the turbine with a single
runner (think of a 4-into-1 exhaust). This design causes
the exhaust gases to collide and interfere with one
another, reducing the strength of the flow.
In contrast, a twin-scroll turbocharger gathers exhaust
from pairs of cylinders in alternating sequence. This
design maximizes pulse energy to the turbine wheel.
The result is a quicker torque delivery (reduced lag).
3 Turbine wheel
4 Housing
The system allows a maximum of 20 seconds of engine
overboost. After 20 seconds the system automatically
ramps down the turbo boost to a predetermined max
limit.
Once the turbo boost drops below the predetermined
limit the system resets and a further 20 seconds of
engine overboost is permitted.
NOTE: The engine management system automatically
controls overboost.
Turbocharger
1
41