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/InstallationTransmission/Transaxle SST
1: Mazda SST number
2: Global SST number
Example
1:49 UN30 3009
2:303-009
Crankshaft damper remover
Clutch [C66M-R]
1:49 E011 1A0
2: –
Ring gear brake set
1:49 SE01 310A
2: –
Clutch disc center ...
Front Under Cover No.1 Removal/Installation
1. Remove bolts A.
2. Remove screws B.
3. Remove fasteners C.
4. Remove the front under cover No.1 in the direction of the arrow in the order
of (1), (2) shown in the figure while detaching the guide D.
5. Install in the reverse order of removal. ...
Camshaft Position (CMP) Sensor
Purpose/Function
Detects the camshaft speed as basic information for mainly determining the
fuel injection timing and ignition timing.
Detects the camshaft speed and inputs it to the PCM as a CMP signal.
Construction
Intake CMP sensor
Installed on the cylinder head.
...