Manifolds and exhaust systems - V8 (Description): 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 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.