the main problems with turbochargers is that they do not provide
an immediate power boost when you step on the gas. It takes
a second for the turbine to get up to speed before boost is
produced. This results in a feeling of lag when you step on
the gas, and then the car lunges ahead when the turbo gets
One way to decrease turbo lag is to reduce the inertia of
the rotating parts, mainly by reducing their weight. This
allows the turbine and compressor to accelerate quickly, and
start providing boost earlier. One sure way to reduce the
inertia of the turbine and compressor is to make the turbocharger
smaller. A small turbocharger will provide boost more quickly
and at lower engine speeds, but may not be able to provide
much boost at higher engine speeds when a really large volume
of air is going into the engine. It is also in danger of spinning
too quickly at higher engine speeds, when lots of exhaust
is passing through the turbine.
turbocharger can provide lots of boost at high engine speeds,
but may have bad turbo lag because of how long it takes to
accelerate its heavier turbine and compressor. Luckily, there
are some tricks used to overcome these challenges.
turbochargers have a wastegate, which allows the use of a
smaller turbocharger to reduce lag while preventing it from
spinning too quickly at high engine speeds. The wastegate
is a valve that allows the exhaust to bypass the turbine blades.
The wastegate senses the boost pressure. If the pressure gets
too high, it could be an indicator that the turbine is spinning
too quickly, so the wastegate bypasses some of the exhaust
around the turbine blades, allowing the blades to slow down.
use ball bearings instead of fluid bearings to support the
turbine shaft. But these are not your regular ball bearings
-- they are super-precise bearings made of advanced materials
to handle the speeds and temperatures of the turbocharger.
They allow the turbine shaft to spin with less friction than
the fluid bearings used in most turbochargers. They also allow
a slightly smaller, lighter shaft to be used. This helps the
turbocharger accelerate more quickly, further reducing turbo
turbine blades are lighter than the steel blades used in most
turbochargers. Again, this allows the turbine to spin up to
speed faster, which reduces turbo lag.
use two turbochargers of different sizes. The smaller one
spins up to speed very quickly, reducing lag, while the bigger
one takes over at higher engine speeds to provide more boost.
is compressed, it heats up; and when air heats up, it expands.
So some of the pressure increase from a turbocharger is the
result of heating the air before it goes into the engine.
In order to increase the power of the engine, the goal is
to get more air molecules into the cylinder, not necessarily
more air pressure.
How a turbocharger is plumbed (including the charge air
An intercooler or charge air cooler is an additional component
that looks something like a radiator, except air passes through
the inside as well as the outside of the intercooler. The
intake air passes through sealed passageways inside the cooler,
while cooler air from outside is blown across fins by the
engine cooling fan.
further increases the power of the engine by cooling the pressurized
air coming out of the compressor before it goes into the engine.
This means that if the turbocharger is operating at a boost
of 7 psi, the intercooled system will put in 7 psi of cooler
air, which is denser and contains more air molecules than
at High Altitudes
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.
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
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.