To keep it brief and simple, a turbo unit compresses the intake of the engine by means of a fan. Essentially, the fan pulls in air on one side and then it pushes it out the other ( it's referred to as the compressor wheel). A fan performs the function of moving air; however we are still left with the task of compressing the air. In order to compress the air; we must then contain it within an enclosed space (this is the compressor housing). Once the intake is compressed it gets sent out to the engine. This process of compression is what's technically referred to as "boost". When one is running more "boost" this person is essentially running more compressed air out of his turbo unit. This is usually related to the size of the unit itself. However, certain factors can limit the degree to which boost varies with the size of the unit. As this gets too technical within the scope of the article.
The Turbine Side:-
So far we understand how the compressor side allows for more air to flow into the engine, but we must now understand what it is that makes the compressor wheel turn fast enough to create the boost in the first place. In turn, we are brought into the turbine side. A turbine is a term used to describe a fan like object that gets propelled by the flow of air, water or steam. In a hydroelectric power plant, the Turbine is propelled by the flow of water which then turns a generator. Within the scope of the turbo charger, the turbine is propelled by the flow of exhaust gases that come out of the engine. So the more exhaust that flows out of the engine, the faster the turbine will turn. Again, like the intake side, pressure can only be created if the flow of air is kept within an enclosed space; for this reason, we have the turbine housing.
Ups and Downs of Turbo Chargers:-
So what does a turbo charger do then you ask? Well, it basically allows you to get more power out of a smaller engine. So in a car that would normally require 6 cylinders, you can now run 4 and still get close to the same power without the added weight and increased gas consumption.
While the turbo unit does provide ample cranking power, it is very dependant on the reciprocating process which I described earlier. This implies that we must somehow power the unit before it begins to give us anything in return. So its one of those deals where you got to give it something before it gives you anything in return. You can think of it as one of those greedy bastards you run across in life. He'll help you as long as you do something for him first. Within the framework of the article, the turbo unit requires exhaust pressure to turn before it begins to provide any added boost to the engine. As a result, what happens is that engines equipped with turbo units take a little while before they give off the power. So at lower RPM's you'll find that you don't get that instant throttle response that you would otherwise get in a naturally aspirated system. This is because the intake and exhaust functions of the engine are not intertwined much like they are in forced induction systems. However, in order to overcome this, turbo charged engines can be driven at higher RPM's. In turn, this keeps the unit constantly turning and fully ready to give off the extra pressure on demand. Of course, as most of you are already aware, this would in turn result in greater wear and tear on the engine and greater gas consumption. However, technology has allowed for many of the downsides of turbo units to be more or less overcome.
These issue that must be addressed relates to the manner in which power is delivered through a turbo charged engine. Basically, the turbo system is quite sporadic. Meaning, it's sometimes hard for more novice drivers to know where and how the power is going to be brought on. Turbo charged cars tend to take a little while before any boost is generated, so the driver may find himself pressing down pretty far on the gas under 2 500 RPM's. However, once the boost is brought on, the driver would then experience a great jolt. This jolt, if not accommodated properly can send a rear wheel drive car into a severe drift. In some set-ups, this can be very lethal. An example would be a rear engine, turbo charged rear wheel drive car, much like the older 911 Turbo's. This partially helps explain why most 911's now come equipped with all wheel drive and state of the art traction control systems.