L322 Range Rover System Description and Operation
ENGINE MANAGEMENT SYSTEM – V8
18-2-42 DESCRIPTION AND OPERATION
A = Valve lift
B = Crankshaft rotation
C = Open duration 228
°
D = Open duration 236
°
E = Default retard
F = Maximum retard
G = Exhaust valve
H = Intake valve
The design of a camshaft for a non adjustable valve timing system is limited to the required overall performance of
the engine.
An intake camshaft with an advanced (early) profile will provide a higher performing power curve at a lower engine
speed. But at idle speed the advanced position will create a large area of intake/exhaust overlap that causes a rough,
unstable idle.
An intake camshaft with a retarded (late) profile will provide a very smooth, stable idle but will lack the cylinder filling
dynamics needed for performance characteristics at mid range engine speeds.
The ability to adjust the valve timing improves the engines power dynamics and reduces exhaust emissions by
optimising the camshaft angle for all ranges of engine operation. VCC provides the following benefits:
l
Increased torque at lower to mid range engine speeds without a loss of power in the upper range engine speeds
l
Increased fuel economy due to optimised valve timing angles
l
Reduction of exhaust emissions due to optimised valve overlap
l
Smoother idle quality due to optimised valve overlap.
M18 0826
B
H
E
F
A
G
C
D
