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/InstallationAssist Handle Removal/Installation
Removal
1. Insert a tape-wrapped flathead screwdriver into the service hole and remove
the assist handle covers.
2. Remove the assist handle in the direction of the arrow (1) and (2), while
detach clips.
NOTE:
Remove the assist handle by shaking it up and down.
Install ...
Rocking the Vehicle
WARNING
Do not spin the wheels at more than 56 km/h (35 mph), and do not allow anyone
to stand behind a wheel when pushing the vehicle: When the vehicle is stuck, spinning
the wheels at high speed is dangerous. The spinning tire could overheat and explode.
This could cause serious injuries.
...
Air Intake Actuator Inspection [Full Auto Air Conditioner]
1. Connect battery positive voltage to air intake actuator terminal B (or C),
connect terminal C (or B) to ground, and then verify that the air intake actuator
operates as shown in the table.
If the operation condition is not normal, replace the air intake actuator.
...