Figure 5-41.Vane-type supercharger.
The supercharger raises the air pressure in the
engine intake manifold. Then, when the intake valves
open, more air-fuel mixture (gasoline engine) or air
(diesel engine) can flow into the cylinders. An
intercooler is used between the supercharger outlet and
the engine to cool the air and to increase power (cool
charge of air carries more oxygen needed for
A supercharger will instantly produce increased
pressure at low engine speed because it is mechanically
linked to the engine crankshaft. This low-speed power
and instant throttle response is desirable for passing and
entering interstate highways.
A turbocharger is an exhaust-driven supercharger
(fan or blower) that forces air into the engine under
pressure. Turbochargers are frequently used on small
gasoline and diesel engines to increase power output.
By harnessing engine exhaust energy, a turbocharger
can also improve engine efficiency (fuel economy and
The turbocharger (fig. 5-42) consists of three basic
partsa turbine wheel; an impeller or compressor; and
housings that support the parts and direct the flow of
exhaust gases and intake air. Basic operation of a
turbocharger is as follows:
When the engine is running, hot gases blow out
the open exhaust valves and into the exhaust
Figure 5-42.Turbocharger (cutaway view).
manifold. The exhaust manifold and connecting
tubing route these gases into the turbine housing.
As the gases pass through the turbine housing,
they strike the fins or blades on the turbine
wheel. When engine load is high enough, there
is enough exhaust gas flow to spin the turbine
Since the turbine wheel is connected to the
impeller by the turbo shaft, the impeller rotates
with the turbine. Impeller rotation pulls air into
the compressor housing. Centrifugal force
throws the spinning air outward. This causes air
to flow out of the turbocharger and into the
engine cylinder under pressure.
A turbocharger is located on one side of the engine.
An exhaust pipe connects the exhaust manifold to the
The exhaust system header pipe
connects to the outlet of the turbine housing.
Theoretically, the turbocharger should be located as
close to the engine manifold as possible. Then a
maximum amount of exhaust heat will enter the turbine
housing. When the hot gases move past the spinning
turbine wheel, they are still expanding and help rotate
Turbocharger lubrication is required to protect the
turbo shaft and bearings from damage. A turbocharger
can operate at speeds up to 100,000 rpm. For this
reason, the engine lubrication system forces oil into the
turbo shaft bearings. Oil passages are provided in the
turbo housing and bearings and an oil supply line runs
from the engine to the turbocharger. With the engine
running, oil enters the turbocharger under pressure. A