found this why i was looking for something online for it might be helpful for people who don't really understand about turbos.
Turbocharger's operate as an exhaust driven method of increasing Intake air flow. They differ in one way from superchargers as they do not require a direct mechanical connection to the engine. So, you don't have to worry about snapped blower belts!
The basic operation of a turbocharger can be explained as thus: The exhaust gasses exit the combustion chamber into the header and then enter the turbine housing. When engine speed & load is high enough the exhaust gas hits the turbine with enough momentum to start spinning it. Rapid expansion of the exhaust gasses create a vortex air flow which spins the turbine in excess of 100,000 RPM's. The turbine wheel (the hot wheel) is attached by a shaft to the intake compressor wheel (the cold wheel). When the turbine wheel is sufficiently spinning the compressor wheel spins & draws in fresh air. Air exits under pressure through the rest of the induction system into the cylinders.
The components that make up a turbocharger are:
Housing - Contains the bearings, shaft, turbine seal assembly, compressor seal assembly & lubrication passages. Some Turbo's may also have a coolant passage. This is the part usually right next to the Header.
Compressor Wheel - Located in the Housing in the Intake airstream. Driven by the Turbine Wheel. Has curved fins opposite of the turbine wheel. Air is drawn into the center and forced outward by centrifugal force. THIS AIRFLOW IS WHAT CAUSES BOOST!!!
Turbine Wheel - Located in the housing in the exhaust gas stream. Torque generated by the Turbine Wheel spins the Compressor Wheel. It has curved fins opposite of the compressor wheel that when exhaust gasses hit the fins create a vortex airflow which spin the wheel which spins the Compressor Wheel for BOOST!
The Shaft - Attaches the Turbine Wheel & Compressor Wheel. The shaft is supported by free-floating bearings which are lubricated by engine oil.
Wastegate Valve - Located in Turbine Wheel exhaust airstream. The valve is actuated by manifold BOOST pressure. It is closed when the Turbo is actuated, so that maximum exhaust energy is directed to the Turbine Wheel. The valve opens to allow a certain amount of exhaust gas to to bypass the Turbine Wheel once desired air pressure is reached. The Wastegate Valve can be summed up as - Flow of exhaust reaching Turbine decreases-This reduces Turbine/Compressor speed-Valve stabilizes turbo air pressure-Valve helps prevent detonation (Bad)
Intercooler - Cools air compressed by Turbo before it enters the combustion chamber. This makes the Air intake charge more dense, Denser air contains more Oxygen, More Power! Making air cooler & denser increases horsepower and it helps to resist detonation.
Compressor Bypass Valve - In the CBV the pressurized air is rerouted to the Compressor inlet for reuse. The CBV is actuated under positive vacuum conditions & is closed shut when positive BOOST pressure is reached in the manifold. When going through the gears on your Volvo, a short-lived vacuum condition is created & the CBV opens to direct the pressurized air back to the Turbo in inlet. CBV's are an O.E.M. part that can be found on all Bosch-K & LH-Jet E.F.I. systems.
Those are the basic components of the Turbocharger system.
Fun Stuff -
Boost Controllers come in 2 types -
Manual Boost Controller - Uses an operator adjusted gate valve to control the Boost pressure acting upon the Wastegate. By adjusting the pressure available to the Wastegate, more or less intake BOOST pressure can be generated.
Electronic Boost Controller - Uses a solenoid actuated by a control module that relies on either the vehicle's existing manifold pressure sensor or it can use an auxiliary one. The solenoid controls BOOST pressure acting upon the Wastegate. The controller can be programmed for more than one BOOST level on some units.
Blow-Off Valve - Reduces pressure in the Intake when the throttle is released, preventing air ducting from blowing apart and protecting the Compressor Wheel from Surge. The valve is actuated by a High vacuum signal from behind the closed throttle. This is the component that makes the "whoosh" sound on a turbocharged vehicle.
Bad Stuff -
Turbo Lag - The time required to bring the turbo up to a speed where it can function effectively is called turbo lag. This is noticed as a hesitation in throttle response when coming off idle. This is symptomatic of the time taken for the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its rotational inertia and reach the speed necessary to supply boost pressure. The directly-driven compressor in a supercharger does not suffer this problem. On light loads or at low RPM a turbocharger supplies less boost and the engine is less efficient than a supercharged engine. Lag can be reduced by lowering the rotational inertia of the turbine, for example by using lighter parts to allow the spool-up to happen more quickly. Ceramic turbines are a big help in this direction. Unfortunately, their relative fragility limits the maximum boost they can supply. Another way to reduce lag is to change the aspect ratio of the turbine by reducing the diameter and increasing the gas-flow path-length. Increasing the upper-deck air pressure and improving the wastegate response helps but there are cost increases and reliability disadvantages that car manufacturers are not happy about. Lag is also reduced by using a foil bearing rather than a conventional oil bearing. This reduces friction and contributes to faster acceleration of the turbo's rotating assembly. Variable-nozzle turbochargers eliminate lag. Lag can be reduced with the use of multiple turbochargers. Another common method of equalizing turbo lag is to have the turbine wheel "clipped", or to reduce the surface area of the turbine wheel's rotating blades. By clipping a minute portion off the tip of each blade of the turbine wheel, less restriction is imposed upon the escaping exhaust gases. This imparts less impedance onto the flow of exhaust gases at low RPM, allowing the vehicle to retain more of its low-end torque, but also pushes the effective boost RPM to a slightly higher level. The amount of turbine wheel clipping is highly application-specific. Turbine clipping is measured and specified in degrees. Lag is not to be confused with the boost threshold; however, many publications still make this basic mistake. The boost threshold of a turbo system describes the minimum engine RPM during full-throttle operation at which there is sufficient exhaust flow to the turbo to allow it to generate significant amounts of boost[citation needed]. Newer turbocharger and engine developments have caused boost thresholds to steadily decline to where day-to-day use feels perfectly natural. Putting your foot down at 1200 engine RPM and having no boost until 2000 engine RPM is an example of boost threshold and not lag. If lag was experienced in this situation, the RPM would either not start to rise for a short period of time after the throttle was increased, or increase slowly for a few seconds and then suddenly build up at a greater rate as the turbo become effective. However, the term lag is used erroneously for boost threshold by many manufacturers themselves. Electrical boosting ("E-boosting") is a new technology under development; it uses a high speed electrical motor to drive the turbocharger to speed before exhaust gases are available. The electric motor is about an inch long.
Race cars often utilize an Anti-Lag System to completely eliminate lag at the cost of reduced turbocharger life. On modern diesel engines, this problem is virtually eliminated by utilizing a variable geometry turbocharger.
Damage - Turbochargers can be damaged by dirty or ineffective oil, and most manufacturers recommend more frequent oil changes for turbocharged engines. Many owners and some companies recommend using synthetic oils, which tend to flow more readily when cold and do not break down as quickly as conventional oils. Because the turbocharger will heat when running, many recommend letting the engine idle for one to three minutes before shutting off the engine if the turbocharger was used shortly before stopping (most manufacturers specify a 10-second period of idling before switching off to ensure the turbocharger is running at its idle speed to prevent damage to the bearings when the oil supply is cut off). This lets the turbo rotating assembly cool from the lower exhaust gas temperatures, and ensures that oil is supplied to the turbocharger while the turbine housing and exhaust manifold are still very hot; otherwise coking of the lubricating oil trapped in the unit may occur when the heat soaks into the bearings, causing rapid bearing wear and failure when the car is restarted. Even small particles of burnt oil will accumulate and lead to choking the oil supply and failure. This problem is less pronounced in diesel engines, due to the lower exhaust temperatures and generally slower engine speeds. A turbo timer can keep an engine running for a pre-specified period of time, to automatically provide this cool-down period. Oil coking is also eliminated by foil bearings. A more complex and problematic protective barrier against oil coking is the use of watercooled bearing cartridges. The water boils in the cartridge when the engine is shut off and forms a natural recirculation to drain away the heat. Nevertheless, it is not a good idea to shut the engine off while the turbo and manifold are still glowing. In custom applications utilizing tubular headers rather than cast iron manifolds, the need for a cooldown period is reduced because the lighter headers store much less heat than heavy cast iron manifolds. Turbochargers can also suffer bearing damage and premature failure due to throttle blipping right before shutdown. This may cause the turbo to continue spinning after the engine has shutdown and oil pressure has dropped.
