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.
...
Fuel and Engine Exhaust Precautions
Fuel Requirements
Vehicles with catalytic converters or oxygen sensors must use ONLY UNLEADED FUEL,
which will reduce exhaust emissions and keep spark plug fouling to a minimum.
Your Mazda will perform best with fuel listed in the table.
Fuel with a rating lower than 87 octane (91 RON) could ...
Fuel Filler Cap
Purpose, Function
Releases evaporative gas from the fuel tank if there is a malfunction in
the evaporative gas passage between the fuel tank and the intake manifold. As
a result, deformation of the fuel tank caused by evaporative gas pressure is
prevented.
Construction
T ...