A Turbocharger is a forced induction system
Compressing the incoming charge of fuel and air increases the power available from an engine. Turbos use the waste exhaust gas flow from the engine to power a turbine which rotates a compressor at very high speed. The compressor forces an increased amount of fuel/air into the engines cylinders, placing a greater strain on pistons, bearings and the drive train. The resulting increase in power shows that it is possible produces more power than the same engine without the turbo. This increases power to weigh ratio.

A turbo allows the engine to burn more fuel and air by forcing more into the cylinders. The standard boost from a turbo is 6 – 8 PSI (pounds per square inch). Normal atmospheric pressure is 14.7, so you are getting an extra 50% more air into the engine and expecting 50% more power. It will actually provide a 30 – 40% improvement. This is because a turbo is not perfectly efficient, as it uses the air from the exhaust to drive the turbine the exhaust flow becomes restricted.

Turbos are bolted to the exhaust manifold of the engine. The exhaust flow from the engine spins the turbine, which is connected by a shaft to the compressor located between the air filter and the manifold air intake.

When air is compressed, it will become more dense. So some of the air pressure from the turbo is a result of the heated air before it enters the engine. In order to get more power the aim is to get more air molecules into the engine, not necessarily more pressure. Cooler air is denser and contains more air molecules than warmer air. An intercooler can be used to cool the air before it enters the engine.

The Turbocharger consists of several basic parts:
Turbine, shaft, bearings, compressor and housings. Exhaust gas pressure spins the turbine , which compresses the incoming air.

Too Much Boost
The compressed air from the turbo is pumped into the cylinder and then further compressed by the piston, There is more danger of knocking, this because as the air is compressed the temperature of the air increases and can increase enough to ignite before the spark plug sparks. Cars with turbos usually need to run on a higher octane fuel to avoid knocking.

Turbo lag
Turbo lag is the lack of immediate power boost when you put the foot down. It takes a second for the turbine to get up to speed before boost is produced. To limit turbo lag you need to reduce the weight of the turbos moving parts. Some turbos use a ceramic blade, as it is lighter and will allow the turbine to spin up to speed more quickly and therefore produce boost quicker.

Small Vs Large Turbochargers
Small turbos provide boost more quickly as they spin up to speed faster at lower engine revs, but may be limited boost at higher engine revs. A larger turbo will produce a more boost at higher engine revs but will have greater lag as it is slower to spin up to speed because of its heavier turbine and compressor.

The Wastegate
Most turbos have a wastegate. The wastegate allows the use of a smaller turbo to limit lag whilst preventing it from spinning too fast at high engine revs. Excess turbine pressure operates a wastegate valve which releases exhaust gases directly into the exhaust pipe, passing the turbine. This allows the turbine to slow down.

Ball Bearings Vs Fluid Bearings
Most turbos use fluid bearings to support the turbine shaft however ball bearings allow the turbine shaft to spin with less friction. The ball bearings are made from advanced materials to handle the speed and temperature they also have a smaller lighter shaft that will spin up quickly and reduce turbo lag.

Sequential Turbos
Some engines use two different sized turbos. The small one spins up very quickly reducing lag and the larger one takes over at higher revs to produce more boost.

Intercooler
Some cars have an intercooler, which is an additional part that cools the pressurised air from the compressor before it enters the engine. An Intercooler looks similar to a radiator and works in a similar way but cooling air rather than water. Intake air passes through the sealed passages inside the intercooler whilst cooler outside air is blown through the intercooler fins by the engine fan or forced by the movement of the vehicle.