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/InstallationFront Side Frame (Partial Cutting) Installation [Panel Replacement]
Symbol Mark
Installation Procedure
CAUTION:
The cut and joint area indicates the maximum size range of the installation
position.
1. Drill holes for the plug welding before installing the new parts.
2. When installing the new parts, trial-fit new and existing parts, and then ...
Miller Cycle Engine
Outline
The Miller cycle engine is a high-efficiency engine which achieves high fuel
economy performance by obtaining a high-expansion ratio.
The Miller cycle engine achieves a high-expansion ratio without increasing
its effective compression ratio by retarding the intake air va ...
Break-In Period
No special break-in is necessary, but a few precautions in the first 1,000 km
(600 miles) may add to the performance, economy, and life of your Mazda.
• Do not race the engine.
• Do not maintain one constant speed,
either slow or fast, for a long period of time.
• Do not drive constantl ...