Purpose, Function
By lengthening the exhaust passage, the transmission of exhaust pressure waves to other cylinders can be delayed, and the amount of gas exhausted from a cylinder and forced back inside the combustion chamber is reduced By reducing the residual gas, the temperature inside the combustion chamber is reduced and the occurrence of knocking even at a high compression ratio is inhibited.
Construction
The exhaust manifold is installed to the rear of the engine. In addition, the catalytic converter (WU-TWC) is integrated (WU-TWC).

When the No.1 cylinder is at the intake stroke, the No.3 cylinder is at the exhaust stroke. By inducing the high temperature gas exhausted from the No.3 cylinder into the No.1 cylinder, the high temperature gas in the No.1 cylinder remains. If the amount of residual gas is high, the temperature in the combustion chamber rises and knocking can easily occur. With the 4-2-1 exhaust system, the transmission of exhaust pressure waves between each cylinder is delayed by the long exhaust pipes.

Exhaust System Removal/InstallationGenerator Removal/Installation [Skyactiv G 2.0]
WARNING:
Remove and install all parts when the engine is cold, otherwise they can
cause severe burns or serious injury.
When the battery cables are connected, touching the vehicle body with generator
terminal B will generate sparks. This can cause personal injury, fire, and ...
Rear Body Control Module (Rbcm)
Outline
Positioned at the rear of the vehicle, the rear body control module (RBCM)
performs numerous system controls for functions at the vehicle rear.
Function
The rear body control module (RBCM) controls the system based on the input/output
signals.
The functions ...
Positive Crankcase Ventilation (PCV) Valve
Purpose, Function
Prevents release of blow-by gas (unburnt gas) into the atmosphere.
The PCV valve is open/closed by the intake manifold vacuum.
Construction
The PCV valve is installed to the oil separator.
The PCV valve consists of a spring and valve.
...