Discovery 2. Manual — part 103

MANIFOLDS AND EXHAUST SYSTEMS - V8

DESCRIPTION AND OPERATION

30-2-5

Description

General
The inlet manifold on the V8 engine is located on the top of the engine, between the cylinders. The manifold directs
intake air into the cylinders. The intake air is mixed with fuel delivered by the injectors prior to ignition in the cylinders.
The inlet manifold comprises three separate aluminium castings.

Two exhaust manifolds are used, one for each bank of four cylinders. Each exhaust manifold allows combustion
gases from the cylinders to leave the engine and directs them into the exhaust system.

The exhaust system is connected to each exhaust manifold and merges into one pipe midway along the underside of
the vehicle. A catalytic converter (where fitted) is located in the front pipe from each manifold. A silencer is installed
midway along the system and a second tail silencer is located at the rear of the vehicle.

Inlet manifold
The inlet manifold comprises three aluminium castings; a lower manifold, an upper manifold and a plenum. The inlet
manifold is located on the top of the engine and feeds air into the cylinders.

Lower manifold
The lower manifold is a one piece machined aluminium casting which locates in the vee on the top of the engine and
is secured to each cylinder head with six bolts per head. A one piece coated metal gasket seals the lower manifold to
each cylinder head and also serves as a cover for the cylinder block.

Eight injectors are fitted into the lower manifold, four on each side. Each injector is sealed in the manifold with O-ring
seals and retained in position by the fuel rails. A fuel rail is attached to each side of the manifold and secured with two
bolts.

Eight air intake ports are cast and machined on the top of the manifold, each port directing intake air into one cylinder.
These ports mate with matching ports in the upper manifold and are sealed with a coated metal gasket between the
two manifolds.

A cavity at the front of the manifold collects coolant flow from the engine. A coolant outlet pipe is sealed and attached
to the front of the manifold and provides for coolant to flow through the cavity in the casting to the radiator top hose.
A smaller port in the manifold also allows coolant to flow from the cavity to the heater matrix. The lower manifold also
locates the Engine Coolant Temperature (ECT) sensor in a port in the front of the manifold.

Upper manifold
The upper manifold is a one piece machined aluminium casting. The manifold has eight ports on its lower face which
mate with the eight ports on the lower manifold. The joint between the upper and lower manifolds is sealed with a
coated metal gasket and secured with six bolts.

The manifold divides from the eight ports into eight branches, four on each side. Each set of four branches merge into
one gallery on each side of the manifold. Each gallery has an opening at its forward end which mates with the intake
plenum.

The upper manifold provides attachment for the Idle Air Control (IAC) valve and for brackets which retain pipes, plug
leads and throttle cables.

Inlet plenum
The plenum is mounted transversely on the front of the upper manifold. The plenum divides into two galleries which
connect with the galleries on the upper manifold. The plenum is secured to the upper manifold with four bolts and
sealed with a coated metal gasket.

The plenum provides attachment for the throttle housing, which is secured with four bolts and sealed with a coated
metal gasket. The plenum also has vacuum connections for brake servo, rocker cover breather and fuel vapour from
the charcoal canister. A port on the top of the plenum connects via a hose to the IAC valve.

MANIFOLDS AND EXHAUST SYSTEMS - V8

30-2-6

DESCRIPTION AND OPERATION

Exhaust manifolds
Two handed, cast iron exhaust manifolds are used on the V8 engine. Each manifold has four ports which merge into
one flanged outlet positioned centrally on the manifold.

Each manifold is attached to its cylinder head with eight Torx bolts. Each bolt is fitted with a 'cotton reel' shaped spacer
which allows for a longer bolt resulting in increased torque loading on each bolt. Two laminated metal gaskets seal
each manifold to its cylinder head. The flanged outlet on each manifold provides the attachment for the front pipe of
the exhaust system.

Exhaust system
The exhaust system comprises a front pipe assembly with two front pipes each incorporating a catalytic converter, an
intermediate pipe incorporating a silencer and a tail pipe assembly which also has a silencer. The exhaust system is
constructed mainly of 63 mm (2.48 in) diameter extruded pipe with a 1.5 mm (0.06 in) wall thickness. All pipes are
aluminized to resist corrosion and the silencers are fabricated from stainless steel sheet.

Front pipe assembly
The front pipe assembly is of welded and fabricated construction. A front pipe from each exhaust manifold merges
into one flanged connection. Two captive studs on the flange provide attachment to the intermediate pipe with
locknuts. Each front pipe has a welded flange which is attached to each manifold and secured with three studs and
flanged nuts and sealed with a metal laminated gasket. The gasket comprises a heat resistant fibre between two thin
metallic layers to enhance the sealing properties of the gasket.

A catalytic converter is located in each front pipe. The catalytic converters are different shapes to allow clearance
between the body and transmission. Both catalytic converters are of similar internal construction.

+

EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Emission Control Systems.

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.

From the catalytic converters, the front pipes merge into one pipe which terminates at a flanged joint. The flange
connects with the intermediate pipe, sealed with an olive and secured with studs and locknuts.

Intermediate pipe and silencer
The intermediate pipe is of welded and fabricated tubular construction. It connects at its forward end with a flange on
the front pipe assembly and is secured with locknuts to captive studs in the front pipe assembly flange. The rear
section of the intermediate pipe connects to the tail pipe assembly via a flanged joint, sealed with a metal gasket and
secured with locknuts and studs.

The forward and rear sections are joined by a silencer. The silencer is fabricated from stainless steel sheet to form
the body of the silencer. An end plate closes each end of the silencer and is attached to the body with seam joints.
Perforated baffle tubes inside the silencer are connected to the inlet and outlet pipes on each end plate. Internal baffle
plates support the baffle tubes and together with a stainless steel fibre absorb combustion noise as the exhaust gases
pass through the silencer.

The intermediate pipe is attached by two brackets, positioned at each end of the silencer, and mounting rubbers to
the chassis. The mounting rubbers allow ease of alignment and vibration absorption. The two mounting rubbers are
fitted with removable heat deflectors to prevent heat from the silencer damaging the material.

Tail pipe assembly
The tail pipe is of welded and fabricated construction. It connects to the intermediate pipe with a flanged joint secured
with studs and locknuts and sealed with a metal gasket. The pipe is shaped to locate above the rear axle allowing
clearance for axle articulation. The pipe is also curved to clear the left hand side of the fuel tank which has a reflective
shield to protect the tank from heat generated from the pipe.

A fabricated silencer is located at the rear of the tail pipe. The silencer is circular in section and is constructed from
stainless steel sheet. A baffle tube is located inside the silencer and the space around the baffle tube is packed with
a stainless steel fibre. The holes in the baffle tube allow the packing to further reduce combustion noise from the
engine. The tail pipe from the silencer is curved downwards at the rear of the vehicle and directs exhaust gases
towards the ground. The curved pipe allows the exhaust gases to be dissipated by the airflow under the vehicle and
prevents gases being drawn behind the vehicle.

The tail pipe is attached by a bracket, positioned forward of the silencer, and a mounting rubber to the chassis. The
mounting rubber allows ease of alignment and vibration absorption.

MANIFOLDS AND EXHAUST SYSTEMS - V8

REPAIRS

30-2-7

REPAIRS

Front pipe

$% 30.10.09

Remove

1. Release front HO2S multiplugs from support

brackets and disconnect multiplugs.

2. Raise vehicle on ramp.

3. Where fitted, release rear HO2S multiplugs

from support brackets on transfer box and
disconnect multiplugs.

4. Remove 8 bolts securing cross member and

remove cross member.

MANIFOLDS AND EXHAUST SYSTEMS - V8

30-2-8

REPAIRS

5. Remove 2 nuts securing front pipe to

intermediate pipe/silencer.

6. Remove 6 nuts securing front pipe to exhaust

manifolds.

7. Release front pipe and collect front pipe to

manifold gaskets.

8. With assistance remove front pipe.
9. Remove HO2S from front pipe.

Refit

1. If refitting existing HO2S, apply anti-seize

compound to HO2S threads.

NOTE: A new HO2 sensor is supplied pre-
treated with anti-seize compound.

2. Fit HO2S to front pipe and tighten to 45 Nm (33

lbf.ft).

3. Clean front pipe and mating faces.
4. Position front pipe, with new front pipe to

manifold gaskets, and align front pipe with
intermediate pipe/silencer and exhaust
manifolds.

5. Fit and tighten exhaust manifold nuts to 30 Nm

(22 lbf.ft).

6. Fit and tighten intermediate pipe/silencer nuts

to 25 Nm (18 lbf.ft).

7. Fit chassis cross member and tighten bolts to

25 Nm (18 lbf. ft).

8. Connect HO2S multiplugs and secure to

support brackets.

Intermediate pipe/silencer

$% 30.10.11

Remove

1. Raise vehicle on ramp.

2. Remove 2 nuts securing intermediate pipe/

silencer to front pipe.

3. Remove 3 nuts securing intermediate pipe/

silencer to tail pipe.

4. Release intermediate pipe/silencer from

mountings and remove intermediate pipe/
silencer.

5. Collect intermediate pipe/silencer to tail pipe

gasket.

Refit

1. Clean intermediate pipe/silencer, front pipe and

tail pipe mating faces.

2. Position intermediate pipe/silencer and locate

on mountings.

3. Using a new intermediate pipe/silencer to tail

pipe gasket, align intermediate pipe/silencer
with tail pipe and front pipe.

4. Fit nuts to intermediate pipe/silencer and

tighten to 25 Nm (18 lbf.ft).