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/InstallationStarter Inspection [Skyactiv G 2.0]
On-vehicle Inspection
1. Verify that the battery is fully charged.
2. The starter is normal if it rotates smoothly and without any noise when the
engine is cranked.
If the starter does not operate, inspect the following:
Remove the starter, and inspect the starter unit.
...
Rear Drive Shaft Inspection
1. Inspect each connecting part for looseness.
Tighten or replace parts if necessary.
2. Inspect the dust boot on the drive shaft for cracks, damage, leaking grease,
and looseness in the boot band.
3. Inspect the drive shaft for bends, cracks, and wear in the joints or splines. ...
Front Oil Seal Replacement
WARNING:
A hot engine can cause severe burns. Turn off the engine and wait until it
is cool before servicing.
1. Remove the front under cover No.2..
2. Remove the splash shield..
3. Remove the drive belt..
4. Remove in the order indicated in the table.
5. Install in the reve ...