Exhaust System: Description and Operation
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 aluminum 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 aluminum 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 aluminum 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 aluminum 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 vapor from the charcoal canister. A port on the top of the plenum connects via a hose to the IAC valve.
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 inch) diameter extruded pipe with a 1.5 mm (0.06 inch) 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 fiber 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.
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 fiber 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 fiber. 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.