Exhaust System: Description and Operation

Description
Inlet Manifolds
The inlet manifold on the KV6 engine is located on the top of the engine, between the cylinder banks. The manifolds direct intake air into the cylinders where it is mixed with fuel delivered by the injectors prior to ignition in the cylinders. The inlet manifold comprises left and right hand cast aluminum inlet manifolds and a plastic molded inlet manifold chamber.
Two handed aluminum inlet manifolds are secured to the cylinder heads using fourteen bolts and sealed with one piece composite gaskets. Three injectors, which are sealed with '0' rings, are located in each manifold and are retained in position by the fuel rail. The fuel rails are secured to each manifold using two bolts. A coolant outlet is located in the left hand end of each manifold and a vacuum take-off point is located on the left hand manifold. Three '0' rings and three molded seals provide the seal between the inlet manifolds and the inlet manifold chamber.

Inlet Manifold Chamber
The inlet manifold chamber is a one piece plastic molding which is fitted on the inlet manifolds and secured with four bolts. Three V rings and three molded seals locate in recesses and seal between the inlet manifold chamber and the inlet manifolds.
The inlet manifold chamber features a single throttle body which feeds into a Y piece, which separates into two secondary pipes. The secondary pipes connect to two main plenums, one for each bank of cylinders. At the closed end of the plenums is a balance valve which is operated by an electric motor. This valve enables the two plenums to be connected together.
From the two plenums, the primary tract length to the cylinder head face is approximately 500 mm. Each of these tracts has a side junction with a power valve leading to a short inlet tract plenum, approximately 350 mm from the cylinder head. Each power valve is connected to a link rod which is operated by a single electric motor.

Front Pipe Assembly
The front pipe is connected to the flanged connections of the left and right hand exhaust manifolds. The front pipe locates on two studs on each manifold and is secured with nuts. A bracket near the front flange is secured to a gearbox attachment bolt. The two manifold pipes merge into an integral flexible pipe which in turn connects with the catalytic converter. The flexible pipe is formed into a concertina shape which is protected by a metal shroud. The flexible pipe allows for ease of exhaust system alignment and also absorbs engine vibrations.
A further pipe section from the catalytic converter is terminated by a flanged connection with captive studs. This pipe section also has a threaded port which provides for the location of the post catalyst H02S. Refer to the Emissions section for details of catalyst and H02S operation.

CAUTION: Ensure the exhaust system is free from leaks. Exhaust gas leaks upstream of the catalytic converter could cause internal damage to the catalytic converter.

Intermediate Pipe Assembly
The intermediate pipe has a flange at its forward end which locates on the three studs on the front pipe and is secured with nuts. The joint between the two flanges is sealed with a metal gasket.
A circular silencer is located midway along the system and is braced to the pipe at each end to resist bending. A short section of pipe from the silencer connects to another smaller rectangular section silencer. A further pipe section from this silencer has a series of bends to allow clearance for the suspension and terminates in an open end which mates with the tail pipe assembly. The intermediate pipe is supported between the flange and the silencer by a welded support bracket and mounting rubber.

Tailpipe Assembly
The tail pipe assembly is of fabricated and welded construction and comprises a large capacity silencer, a connecting pipe and two tail pipes. The curved connecting pipe is welded to the left hand end of the silencer and mates with the intermediate pipe. The connecting pipe is a sliding fit on the intermediate pipe and is secured with a clamp.
Two tail pipes are welded to the right hand end of the silencer and direct exhaust emissions downwards from the right hand end of the bumper.

Exhaust System (NAS)
The manifolds and exhaust system is of welded steel construction and consists of five main parts;
^ A RH (rear) manifold.
^ A LH (front) manifold and catalytic converter.
^ A RH downpipe and catalytic converter.
^ A LH downpipe.
^ An intermediate pipe.
^ A tail silencer.

Close coupled catalytic converters are incorporated into the system to achieve fast converter light-off times after starting the engine. Heated Oxygen Sensors (H02S) are installed upstream and downstream of each catalytic converter, to enable the ECM to exercise closed loop control of the air:fuel ratio and to monitor catalytic converter performance.
To reduce heat loss, the exhaust manifolds, the pipes between the exhaust manifolds and the catalytic converters, and the ends of the catalytic converters, are double walled with an air gap between the walls.
The system is suspended from the underside of the vehicle on mounting rubbers and a bracket on the downpipe and rear catalytic converter.

RH Manifold
The three branch manifold is fitted to the RH cylinder head. A composite gasket seals the manifold to the cylinder head and four studs and nuts secure the manifold in position.

LH Manifold and Catalytic Converter
The front manifold and catalytic converter consists of a three branch manifold and a catalytic converter integrated into a common assembly. A composite gasket seals the manifold to the LH cylinder head and four studs and nuts secure the manifold in position. Threaded bosses are welded into the pipe at each end of the catalytic converter to accommodate the H02S.

RH Downpipe and Catalytic Converter
The RH downpipe and catalytic converter is connected between the RH manifold and the intermediate pipe. The flanged connection with the RH manifold is sealed with a metal gasket. The slip joint connection with the intermediate pipe is secured with a clamp. Threaded bosses are welded into the downpipe at each end of the catalytic converter to accommodate the H02S. A flexible joint is incorporated into the downpipe, near the connection with the intermediate pipe, to absorb engine vibration. Brackets welded to the top of the downpipe accommodate anchor nuts for the attachment of a heatshield.

LH Downpipe
The LH downpipe connects the LH manifold and catalytic converter to the intermediate pipe. Flanged connections at each end of the downpipe are sealed with metal gaskets. A flexible joint is incorporated into the downpipe, near the connection with the intermediate pipe, to absorb engine vibration. A bracing clamp attaches the LH downpipe to the RH downpipe and catalytic converter. A bracket on the LH downpipe attaches the system to the Intermediate Reduction Drive (IRD). Additional brackets welded to the top of the downpipe accommodate anchor nuts for the attachment of a heatshield.

Intermediate Pipe
The intermediate pipe connects the downpipes to the tail silencer. A silencer is incorporated into the front of the intermediate pipe, and the rear end of the pipe is formed to pass over the rear suspension.

Tail Silencer
The tail silencer comprises a silencer, a connecting pipe and two tail pipes. The curved connecting pipe is welded to the left hand end of the silencer and mates with the intermediate pipe. The slip joint between the tail silencer and the intermediate pipe is secured with a clamp.

Operation





Inlet Manifold Chamber-Variable Intake System (VIS)
The VIS operates in three conditions:
^ Low speed
^ Mid-range
^ High speed.

Low Speed
At low speed the balance valve and power valves are closed. This effectively allows the engine to breathe as two, three cylinder engines, each having a separate plenum and long primary tracts. The primary and secondary tracts and the plenum volume are tuned to resonate at 2700 rev/min, giving peak torque at this speed.

Mid-Range
For increased mid-range torque performance, the plenums are connected using the balance valve. The power valves remain closed. This allows the engine to use the long primary tract length, which is tuned with the balance valve to produce maximum torque at 3750 rev/min.

High Speed
At high engine speeds the balance valve remains open and the six power valves are opened. This allows the engine to breathe from the short tract plenum via the short primary tract lengths. These lengths and diameters are tuned to produce a spread of torque from 4000 rev/min upwards, with maximum power produced at 6250 rev/min.
The manifold also gives an improvement in part load fuel consumption. At part load, throughout the emissions cycle the manifold operates as at high speed. The pressure dynamics significantly reduce the pump losses below 4000 rev/ min resulting in improved fuel consumption.