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/InstallationDrive Belt Removal/Installation [Skyactiv G 2.0]
WARNING:
A hot engine can cause severe burns. Turn off the engine and wait until it
is cool before servicing.
NOTE:
Remove/install the drive belt from the underside of the vehicle.
Generator Drive Belt Removal/Installation
CAUTION:
To prevent damage to the dri ...
Fuel Gauge Sender Unit Removal/Installation [2 Wd]
WARNING:
Always keep sparks and flames away from fuel when servicing the fuel system.
Fuel can be easily ignited which could cause serious injury or death, and damage
to equipment.
Fuel line spills and leakage from the pressurized fuel system are dangerous.
Fuel can ignite a ...
Transmission/Transaxle Abbreviations
AAS
Active Adaptive Shift
ABS
Antilock Brake System
ABDC
After Bottom Dead Center
ACC
Accessories
AFS
Adaptive Front Lighting System
ALC
...