Exhaust System: Description and Operation

Exhaust System

COMPONENT LOCATION - NATURALLY ASPIRATED VEHICLES









COMPONENT LOCATION - SUPERCHARGER VEHICLES









INTRODUCTION
The exhaust systems on both NA (naturally aspirated) and SC (supercharger) vehicles are manufactured from stainless steels and have four separate sections:
- LH (left-hand) and RH (right-hand) front sections
- A center section
- A rear section.
The sections of the exhaust system are connected together with slip joints and clamps.

FRONT SECTIONS

NOTE:
LH (left-hand) front section shown, RH (right-hand) front section is mirror image.









Each of the front sections consists of an inlet pipe, a catalytic converter and an outlet pipe welded together. A flange on the inlet pipe connects the front section to the related exhaust manifold on the engine. The flange has two holes which locate on studs in the exhaust manifold and is secured with flanged nuts.
In the catalytic converters, the exhaust gases are passed through honeycombed ceramic elements coated with a special surface treatment called 'washcoat'. The washcoat increases the surface area of the ceramic elements by a factor of approximately 7000. On top of the washcoat is a coating containing palladium and rhodium, which are the active constituents for converting harmful emissions into inert by-products. The palladium and rhodium take oxygen from nitrogen oxides, to leave nitrogen, and combine the oxygen with carbon monoxide and hydrocarbons to leave carbon dioxide and water.

CENTER SECTION

Naturally Aspirated Vehicles









The center section has two inlet and outlet pipes and a muffler all welded together. A plate is welded between the inlet pipes at the front of the center section. Two suspension rubbers connect hangers on the outlet pipes to hangers on the underside of the body.
The muffler consists of an outer case and two end plates, which contain two perforated tubes and a baffle plate.

Supercharger Vehicles









The center section has two inlet, intermediate and outlet pipes, and two mufflers all welded together. Two plates are welded between the inlet pipes at the front of the center section. Two suspension rubbers connect hangers on the outlet pipes to hangers on the underside of the body.
An air deflector shield is attached to four brackets on the outlet pipes. The air deflector shield directs cooling air on to the electronic differential at high vehicle speeds.
The front muffler consists of an outer case and two end plates, which contain two perforated tubes and a baffle plate. The center muffler consists of upper and lower shells, which contain perforated pipes, installed inside over-pipes, and three baffle plates.

REAR SECTION

Naturally Aspirated Vehicles









The rear section has two inlet and outlet pipes welded to a muffler. A polished stainless steel finisher is installed on each of the outlet pipes. Three suspension rubbers connect hangers on the muffler to hangers and a bracket on the underside of the body.
The muffler consists of upper and lower shells, which contain inlet pipes connected to SAM (semi active muffler) valves, and perforated inner pipes supported in five baffle plates. The inner pipes connect to the outlet pipes.
The SAM valves vary the tone of the exhaust to give a more sporty sound at higher engine speeds. The SAM valves are normally closed, spring loaded check valves.
The SAM valves are non serviceable and the muffler is replaced as a complete assembly.

Supercharger Vehicles









The rear section has two inlet pipes and four outlet pipes welded to a muffler. A stiffener plate is welded between each pair of outlet pipes. A polished stainless steel finisher is installed on each of the outlet pipes. Three suspension rubbers connect hangers on the muffler to hangers and a bracket on the underside of the body.
The muffler consists of upper and lower shells, which contain perforated inlet and inner pipes supported in five baffle plates. An exhaust valve is installed in the outboard outlet pipe on each side of the muffler. The exhaust valves are part of the active exhaust system.

Active Exhaust System










The active exhaust system allows exhaust gases to bypass the muffler to produce a more sporty exhaust sound. In addition to the exhaust valves, the active exhaust system has:
- A vacuum pump
- A solenoid valve
- A reservoir
- Related pipes, which incorporate a restrictor and a check valve.
Each exhaust valve consists of a normally open plate valve and pneumatic actuator.
The vacuum pump, solenoid valve and reservoir are attached to a bracket installed in the left rear wheel housing, behind the wheel arch liner. Plastic pipes are connected between the vacuum pump, reservoir and solenoid valve, and between the solenoid valve and the two exhaust valves. The pipes to the RH (right-hand) exhaust valve are located in pipe carriers attached to the rear floor brace.
In the pipes between the solenoid valve and the exhaust valves, a restrictor is installed in parallel with a check valve. The restrictor slows the flow of air through the pipes, to damp the opening of the exhaust valves. The check valve ensures air flows only through the restrictor when the exhaust valves are opened, but allows the restrictor to be by-passed when the exhaust valves are closed, to give an undamped closing movement.
The solenoid valve controls the operation of the exhaust valves by connecting them to the reservoir and vacuum pump or to atmosphere. Atmospheric pressure enters the solenoid valve through a filter attached to a vent.
Operation of the active exhaust system is controlled by the ECM (engine control module).

CONTROL DIAGRAM (SUPERCHARGER VEHICLES ONLY)

NOTE:
A = Hardwired









PRINCIPLES OF OPERATION

Semi Active Muffler Valves (Naturally Aspirated Vehicles Only)
At low engine speeds the SAM valves are closed and restrict the flow through the muffler, which produces a more refined exhaust sound. At higher engine speeds the increased pressure in the exhaust system opens the SAM valves and the increased flow through the muffler produces a sportier exhaust sound.

Active Exhaust System (Supercharger Vehicles Only)
The position of the exhaust valves set by the ECM (engine control module) depends on engine speed, throttle angle and operating mode of the transmission. At startup the exhaust valves are always open, to enhance the exhaust sound.
When the transmission is in the manual (sequential shift) mode, the exhaust valves are permanently open. When the transmission is in the normal or sport mode, the position of the exhaust valves depends on engine speed and load, as detailed in the following table:





The ECM (engine control module) energizes the active exhaust relay in the AJB (auxiliary junction box) 5 seconds after the ignition is switched on. When the relay is energized, it supplies power to the vacuum pump and the solenoid valve. The vacuum pump is connected to ground and runs continuously while the relay is energized, maintaining a depression in the reservoir and pipes to the solenoid valve.
The solenoid valve is connected to ground through the ECM (engine control module). When the ECM (engine control module) determines the exhaust valves require closing, it connects the solenoid valve to ground. When the solenoid valve energizes, it opens the pipe connection from the reservoir and vacuum pump to the exhaust valves, and closes the atmospheric vent. The depression at the reservoir and vacuum pump is then sensed at the exhaust valves, via the check valve, and the exhaust valves close. When the ECM (engine control module) determines the exhaust valves require opening, it disconnects the solenoid valve from ground. The solenoid valve de-energizes and closes the pipe connection to the exhaust valves, and opens the atmospheric vent. Atmospheric pressure is then sensed at the exhaust valves, via the restrictor, and the exhaust valves open.

Active Exhaust System Schematic