Catalytic Converter: Description and Operation
Exhaust System, Emission Control
General information
The exhaust systems in all new Carrera models have been redesigned for direct fuel injection (DFI) in order to achieve maximum performance with minimum emissions.
Design of the exhaust system
The exhaust system for the new 911 models has been completely revised. Newly shaped manifolds, a different position for the catalytic converters and an additional front silencer characterize the new exhaust system. Both the 3.6- and the 3.8-liter engine variants use the same exhaust system. The only distinction between the engines is the revised tailpipe design.
Exhaust gases from cylinder bank 1 (left) flow from the exhaust manifold to the LSU oxygen sensor, though the pre-catalytic converter, to the LSF oxygen sensor, then through the main catalytic converter and the front silencer to the main silencer on the left and then escape through the twin-tailpipe trim on the left. Exhaust gas from cylinder bank 2 (right) accordingly follows the laterally reversed path.
As in the predecessor models, the vehicles with 3.6-liter engines feature two newly formed single tailpipe trim elements. The vehicles with 3.8-liter engine (S models) are equipped with two newly formed dual tailpipe trim elements.
Exhaust manifolds and catalytic converters
The redesigned exhaust manifolds with their nearly equal pipe lengths permit a uniform charge exchange between the cylinders, resulting in balanced combustion processes. Another new feature is the position of the catalytic converters. In the new models, the converters are integrated directly behind the right and left manifold pipes (previously, they were located transversely behind the engine). This location close to the engine and the integration into the manifolds (without an additional flange connection) not only reduces weight, but it also significantly improves the efficiency of the catalytic converters - particularly after cold starting. This measure is a prerequisite for compliance with the new EU5 emissions standard. In combination with the special DFI catalytic-converter heating phase, it is also so efficient that the secondary-air injection that was previously additionally used can now be omitted for the new models.
Moreover, it was possible to relocate the catalytic converters from the crash-sensitive rear area to the side near the engine.
The cascade catalytic converters combine the pre-catalytic converter and the main catalytic converter in the same housing. The substrate of the pre-catalytic converters and main catalytic converters consists of ceramic material.
Emission control
In combination with the new direct fuel injection (DFI), the new exhaust system complies with the EU5 emissions standard for Europe and the LEV/LEV II standard for the USA (predecessor models: EU4 or LEV).
Front silencer
The front silencer, which is located transversely behind the engine, is another new feature supplementing the two main mufflers.
In order to comply with the various world-wide noise emission regulations, different variants of the front silencer with a different internal structure are installed on a country-specific basis.
Exhaust gases from cylinder bank 1 (left) flow from the exhaust manifold through the pre and main catalytic converters to the front silencer, which features a cylinder bank separation in the middle. From here, the exhaust gases flow to the main muffler and escape through the left dual tailpipe cover. Exhaust gas from cylinder bank 2 (right) accordingly follows the laterally reversed path.
Main exhaust muffler
The main mufflers behind the rear quarter panels on the left and right were modified with the addition of a new front silencer and based on the space conditions in connection with the new catalytic converters.
Tailpipe covers
As with the previous models, the tailpipe covers distinguish the new 911 base models from the S variants.
The models with 3.6-liter engine are provided with re-styled single tailpipe covers.
The Carrera S models with 3.8-liter engine also feature re-styled dual tailpipe covers.
