Turbochargers
Basics
One of the surest ways to get more power out
of an engine is to increase the amount of air and fuel that it can burn. One
way to do this is to add cylinders or make the current cylinders bigger.
Sometimes these changes may not be feasible -- a turbo can be a simpler,
more compact way to add power, especially for an aftermarket accessory.

Turbochargers allow an engine to burn more fuel and air by packing more into
the existing cylinders. The typical boost provided by a turbocharger is 6 to
8 pounds per square inch (psi). Since normal atmospheric pressure is 14.7
psi at sea level, you can see that you are getting about 50 percent more air
into the engine. Therefore, you would expect to get 50 percent more power.
It's not perfectly efficient, so you might get a 30- to 40-percent
improvement instead.
One cause
of the inefficiency comes from the fact that the power to spin the
turbine is not free. Having a turbine in the exhaust flow increases the
restriction in the exhaust. This means that on the exhaust stroke, the
engine has to push against a higher back-pressure. This subtracts a little
bit of power from the cylinders that are firing at the same time.
The
turbocharger also helps at high altitudes, where the air is less
dense. Normal engines will experience reduced power at high altitudes
because for each stroke of the piston, the engine will get a smaller mass of
air. A turbocharged engine may also have reduced power, but the reduction
will be less dramatic because the thinner air is easier for the turbocharger
to pump.
Older cars
with
carburetors
automatically increase the fuel rate to match the increased airflow going
into the cylinders. Modern cars with
fuel injection
will also do this to a point. The fuel-injection system relies on oxygen
sensors in the exhaust to determine if the air-to-fuel ratio is correct, so
these systems will automatically increase the fuel flow if a turbo is added.
If a
turbocharger with too much boost is added to a fuel-injected car, the system
may not provide enough fuel -- either the software programmed into the
controller will not allow it, or the pump and injectors are not capable of
supplying it. In this case, other modifications will have to be made to get
the maximum benefit from the turbocharger