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/InstallationSpark Plug [Skyactiv G 2.0]
Purpose, Function
The spark plug generates spark, ignition of the air-fuel mixture occurs,
and combustion of the air-fuel mixture is triggered.
Construction
The spark plug is installed to the cylinder head.
Iridium on the center electrode and platinum on the ...
Coupler Component Removal/Installation [Fw6 A EL, Fw6 Ax EL]
WARNING:
A hot transaxle and ATF can cause severe burns. Turn off the engine and wait
until they are cool.
Always wear protective eye wear when using the air compressor. If the air
compressor is used, any particles of dirt or soiling could spatter and get into
the eyes.
...
Pressure Control Valve Inspection [Skyactiv G 2.0]
1. Remove the pressure control valve assembly..
CAUTION:
Do not apply a pressure 36 kPa {0.37 kgf/cm2, 5.2 psi} or more. Doing so
will damage the pressure control valve and evaporative hose.
2. Apply a pressure of 36 kPa {0.37 kgf/cm2, 5.2 psi} to port A.
3. Verify that ther ...