Copyright by Goodheart-Willcox Co., Inc.
328 Auto Engine Repair
Atmospheric
pressure
Increased
manifold
pressure
Intake Exhaust
Turbocharger
Battery
Belt drive
Increased
manifold pressure
Supercharger
Normal
exhaust exit
Electromagnetic clutch
Wide open
throttle
switch
A
B
Figure 16-1. A comparison of turbocharging and supercharging.
A—A turbocharger is driven by exhaust gasses. It compresses
the incoming air. B—A supercharger also compresses the
incoming air. However, it is normally driven by an engine belt.
A turbocharger has the ability to increase the horse-
power of an engine by as much as 50%. For this reason,
they are commonly used on small displacement engines
to increase performance. Turbochargers, as you will learn,
can increase power under a load, yet have little adverse
affect on fuel economy at cruising speeds.
Superchargers have been used on racing engines for
many years. Manufacturers began installing superchargers
on some production engines a few years ago. Several cars
and trucks now have supercharging to help their engines
develop over 400 horsepower.
To be a competent engine technician, you must have
some knowledge of turbochargers and superchargers.
Many of today’s engines are equipped with these devices.
Normal Aspiration
Normal aspiration means the engine uses only out-
side air pressure (atmospheric pressure) to cause airflow
into the combustion chambers. At sea level, atmospheric
pressure is 14.7 psi (10.1 kPa). With only outside air
pressure to carry oxygen into the engine cylinders, engine
power is limited by the engine’s volumetric efficiency.
Volumetric efficiency is a measure of how much
air the engine can draw in on its intake strokes. A high
volumetric efficiency means the engine “breathes” easily
because of good intake port, valve, combustion chamber,
and camshaft design. However, most engines do not have
high volumetric efficiency. This is because of pumping
losses due to restrictions to airflow through the intake
manifold and cylinder head. As a result, they do not
produce as much horsepower as theoretically possible for
their size.
Turbocharging and supercharging pressurizes the
incoming air. This has the effect of increasing the volu-
metric efficiency. Turbocharging and supercharging are
used on many gasoline and diesel engines to improve
volumetric efficiency and increase power output.
Turbocharging and Supercharging
Turbocharging and supercharging are both methods
of increasing the intake manifold pressure. This forces
more air into the cylinders than normal aspiration. As a
result, power output from the engine is increased.
A turbocharger or turbo is a special fan assembly
that uses engine exhaust gasses to turn the fan blades. A
mechanical linkage with the engine is not needed. Look at
Figure 16-1A.
A supercharger or blower is a special fan assembly
that is driven by a belt on the engine. They are used on
some passenger car engines and can be found on many
racing engines. See Figure 16-1B.
Engine Modifications
Turbocharged and supercharged engines normally
have several modifications to make them withstand the
increased horsepower. A few of these modifications are:
Lower compression ratio.
Stronger rods, pistons, crankshaft, and bearings.
Higher-volume oil pump.
Increased oil capacity.
Larger radiator.
O-ring–type head gasket.
Valves with increased heat resistance.
In addition, an oil cooler may be installed to help keep the
engine oil cool. Oil helps cool the turbocharger. If the oil
gets too hot, the turbocharger can be damaged.