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1 horsepower = 745.699872 Watts

Turbochargers

Turbochargers are a forced induction system.
 They compress the air entering into the engine.
The advantage of compressing the air is that it lets
 the engine accommodate more air into a cylinder,
 more air means more fuel can be added.
Hence, you get more power from each
combustion in the engine. A turbocharged engine
produces more power overall than the same
engine without the turbocharger. This can greatly
 improve the power-to-weight ratio for the engine.

In order to achieve this boost, the turbocharger
 uses the exhaust from the engine to turn a turbine,
 which in turn rotates an air pump. The turbine in
the turbocharger rotates at speeds of up to
150,000 rotations per minute, better known as
RPMs, that is about 30 times faster than the
average car engine turns. And since it is hooked
up to the exhaust, the temperatures
in the turbine are very high.

Basics
One of the best ways to get more power out of your engine is to increase the amount of air and fuel that it will run on. A turbo can be a simple, compact way to add power, especially for an aftermarket power additive.

Turbochargers allow an engine to burn more fuel and air by adding this to the existing cylinders. The average 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 will be getting approximately 50 percent more air into your engine. Hence, you would expect to gain 50 percent more power. It's not always perfect though, so you might get a 30- to 40-percent increase instead.

One cause of the lack in extra power comes from the fact that the power to spin the turbine is taken from elsewhere. Having a turbine in the exhaust flow increases the restriction in the exhaust. This means that on the exhaust stroke, the engine has to work harder against a higher back-pressure. This takes a little bit of power from the cylinders that are firing at that particular time.

The turbocharger also helps in higher elevations, where the air is thinner. Normal engines will experience less power at high elevations because for each stroke of the piston, the engine will get a smaller amount of air. A turbocharged engine may also have loss of power, but the loss 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 engine. Modern cars with fuel injection will also do this to an extent. The fuel-injection system relies on oxygen sensors in the exhaust to determine if the air-to-fuel ratio is is at its proper levels, so these systems should automatically increase the fuel flow if a turbocharger 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 ECM or the controller may not allow it, or the injectors and pump are not capable of supplying it. So other modifications may have to be made to get the greatest benefit from your turbocharger.

How It Works
The turbocharger is bolted to the exhaust manifold on your engine. The exhaust from the engine spins the turbine, which works like a gas turbine engine. The turbine is connected by a shaft to the compressor, which is located between the air filter and the intake manifold. The compressor pressurizes the air going into the pistons.

The exhaust from the cylinders passes through the turbine blades, making the turbine spin. The more exhaust that goes through the blades, the faster they spin.

On the other end of the shaft that the turbine is attached to, the compressor pumps air into the cylinders. The compressor is a type of centrifugal pump. It takes air in at the center of its blades and propels it outward as it spins.

In order to handle rotations of up to 150,000 RPMs, the turbine shaft has to be supported, unlike conventional shafts and bearings. Most bearings would fly apart at speeds of this magnitude, so most turbochargers use a fluid bearing. This type of bearing supports the shaft on a thin layer of oil that is constantly pumped around the shaft. There are two reasons for this: It cools the shaft and some of the other turbocharger parts and it also allows the shaft to spin without much friction.

Too Much Boost
With air being pumped into the engine under pressure by your turbocharger, and then being compressed more by the pistons, there is more danger of knock. Knocking happens because as you compress the air, the temperature of the air rises. The temperature may increase enough to ignite the fuel before the spark plug fires. Vehicles with turbochargers sometimes need to run higher octane fuel to avoid knock. If the boost pressure is really high, the compression ratio of your engine may have to be reduced to avoid knocking.

An intercooler or charge air cooler is an additional component that resembles a radiator, except air flows through the inside as well as the outside of the intercooler. The intake air flows through the sealed intercooler, while cooler air from outside is blown or drawn across fins by the engines cooling fan(s).

The intercooler further increases the power of the engine by cooling the pressurized air coming out of the compressor before it enters the engine. If the turbocharger is operating at a 7 PSI of boost, the intercooled system will put in 7 PSI of cooled air, which is denser and also contains more air molecules then the warmer air that would have went in without the intercooler.

Turbo Lag
One of the biggest problems with turbochargers is that they do not give an immediate power boost when you step on the accelerator. It takes a moment for the turbine to achieve the speed needed before the boost is produced. The result is a feeling of lag when you step on the throttle, and then the vehicle speeds up when the turbo kicks in.

One way to lessen turbo lag is to reduce the inertia of the rotating parts, mostly by reducing their weight. This will allow the turbine and compressor to accelerate quicker and start providing boost quicker.

Small vs. Large Turbocharger
One possible way to reduce the inertia of the turbine and compressor is to make the turbocharger smaller. A small turbocharger will provide boost quicker and at lower engine speeds, but may not be able to provide much boost at higher engine speeds when a large volume of air is going into the engine. It is also in danger of rotating too quickly at higher engine speeds, when lots of exhaust is flowing through the turbine.

A larger turbocharger can provide lots of boost at higher engine speeds, but will probably have bad turbo lag because of how long it takes to accelerate the heavier turbine and compressor.

Optional Turbo Features

The Wastegate
Most automotive turbochargers have a wastegate, which allows the use of a smaller turbocharger to reduce lag while preventing it from rotating too quickly at higher engine speeds. The wastegate is a valve that allows some of 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 rotating too quickly, so the wastegate will bypass some of the exhaust around the turbine blades, allowing the blades to slow down.

Ball Bearings
Some turbochargers use ball bearings instead of fluid bearings to support the turbine shaft. They are super-precise bearings made of special materials to handle the speeds and temperatures of your turbocharger. They allow the turbine shaft to rotate with less friction than the fluid bearings used in most turbochargers. They also allow a slightly smaller and lighter shaft to be used. This helps the turbocharger achieve its boost quicker and further reduces turbo lag.

Ceramic Turbine Blades
Ceramic turbine blades are lighter than steel blades used in most turbochargers. Hence, this allows the turbine to achieve boost speeds faster, which reduces turbo lag.

Sequential Turbochargers
Some engines use two turbochargers of different sizes. The smaller one spins up to speed quickly while reducing lag, while the larger one takes over at higher engine speeds to provide more boost.

Intercoolers
When air 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 your engine. In order to increase the power of your engine, the goal is to get more air molecules into the cylinder, not necessarily more air pressure.

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