Many car enthusiasts
have come across the word "turbo"
without understanding what it stands
for. When asked, very few are
capable of explaining how the
turbocharging system works.
When people talk
about race cars or high-performance
sports cars, the topic of
turbochargers usually comes up.
The word "turbo" has
always been equivalent to "more
power" and "high performance" but
how is this achieved?
It's a simple idea of
compressing air into the cylinders.
The main job of the
turbocharger is to force air into
the engine by compressing it,
therefore allowing more air to fill
the cylinder. More air means that
more fuel can be added, therefore
resulting in an increase in
I would like to
explain turbocharging in a simple
way that anyone with the basic
knowledge of Science can understand
it, but before going further in the
description, I need to go to the
basics of an internal combustion
engine i.e a car engine that runs
either on gasoline or diesel.
The three main
elements that cause a car engine to
run are: fuel, air and a spark.
Inside the engine a
mixture of fuel and air are ignited
by a spark and therefore energy
created by the combustion causes the
engine to run.
The function of
various parts of the engine is to
convert that energy which results
from the combustion of air and fuel,
into a rotational motion.
When the engine is
cranked by turning the ignition key
to the run position, the starter
motor turns the engine and causes
the pistons to move inside the
The downward movement
of the piston inside the cylinder
causes air to be drawn and fill the
cylinder. As the piston moves up to
compress that air, the fuel injector
injects fuel on top of the piston.
So now the compressed air/fuel
mixture is ready to be ignited by
the spark from the spark plug. The
result is an explosion which pushes
the piston down and therefore causes
the engine to keep on turning. The
combustion of the air/fuel mixture
results in burnt gases which are
expelled from the exhaust system.
This cycle repeats
inside all the cylinders in a
sequence and that's how an engine
keeps on running.
A story of two wheels
Refer to the
illustrations below in order to
understand the turbo.Hot
exhaust gases leaving the engine
after combustion are routed directly
to the turbine wheel side of the
turbocharger to make it rotate. That
turbine wheel is connected by a
shaft to a compressor wheel. As the
turbine wheel spins faster and
faster, it causes the compressor
wheel to also spin quickly. The
rotation of the compressor wheel
pulls in ambient air and compresses
it before pumping it into the
The basic principal
behind turbocharging is fairly
simple, but a turbocharger is a very
complex piece of machinery.
Not that simple
In fact there are
lots factors that are taken into
consideration when designing a turbo
Since a turbo can
reach speeds of 150,000 rpm and
since hot exhaust gases pass through
it to spin the turbine wheel, a lot
of heat is generated to a degree
that the turbo can turn into amber
color. The cooling and lubrication
play an essential role in turbo
design as well as the materials
utilized in the design of the
housing, the shaft bushings and the
turbine and compressor blades.
The boost pressure
that a turbo creates can reach up to
1.5 to 2.0 bars. (22-30 psi).
cause damage to the engine piston
and to other parts of the engine.
exhaust gas flow is regulated with a
wastegate that bypasses
excess exhaust gas entering the
turbocharger's turbine, thus
As you may have
guessed, the compressed air leaving
the compressor wheel housing is very
hot as a result of both compression
and friction. So what's needed is a
way to cool that air down before it
enters the cylinders. That's where
an intercooler (or "heat
exchanger") comes in. It reduces the
temperature of the compressed air so
that it is denser when it enters the
cylinders (heat causes things to
expand, as we all learned in science
class). The charge-air cooler also
helps to keep the temperature down
in the combustion chamber.
The turbocharger was
invented by Swiss engineer Alfred
Buchi, who had been working on steam
turbines. His patent for the
internal combustion turbocharger was
applied for in 1905. Diesel ships
and locomotives with turbochargers
began appearing in the 1920s.
first used in production aircraft
engines in the 1930s prior to World
The first production
turbocharged automobile engines came
from General Motors, the A-body
Oldsmobile Cutlass Jetfire in 1962.
BMW led the
resurgence of the automobile turbo
with the 1973 2002 Turbo, with
Porsche following with the 911
Turbo, introduced at the 1974 Paris
Nowadays most car
manufacturers have introduced
turbochargers on some of their
In the racing world
almost all cars are equipped with a
To end this article,
we may conclude that turbocharging
has many benefits.
The benefits of
turbo-charging in both passenger car
and commercial vehicle applications
include greater power and torque for
a given engine size, improved fuel
economy at part throttle and
potentially reduced emissions.
Pascal Johnny Hayek
B. Eng. AUB, 1983 Service Manager
Porsche Service Centre, Kuwait