Manifolds and exhaust systems - V8 (Exhaust manifolds): Description and operation

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.

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.