How does a turbocharger work?

A turbocharger is a blower attached to the same shaft as a turbine. The escaping exhaust gases turn the turbine and cause the blower to turn and compress the air going into the engine. The more air, the more fuel can be burned and so the more energy you get out of the engine.

A supercharger works similarly except that it is driven by a belt or chain that is connected to the crankshaft instead of being driven by the turbine in the exhaust.

A turbocharger consists of two fans on the same axle. The exhaust gasses pass by one of the fans and gets it spinning. Then the other fan on the same axle also starts to spin, and that fan is used to blow more air into the engine. With more air going in the engine can also take more fuel, and with more fuel burned the engine makes more power. A turbocharger is an exhaust driven air compressor. It has an intake compressor wheel driven by a turbine wheel on a common shaft. A turbo only makes positive pressure,"Boost" when the engine is under a load and more power is needed. During cruising a turbo is spinning "relatively slow" not making boost and the engine only takes in the same amount of air as if it wasn't turbocharged. If you floor it/ or drive up a steep hill, the exhaust gas/heat spin the turbo faster and the compressor wheel supplies greater than atmospheric pressure/boost to the engine to increase power. The amount of power depends on factors like base engine configuration (stock or modified) engine HP, rpm range, compressor efficiency, inter-cooler efficiency (if it has one). Turbos have compressor maps to use for selecting the correct one for a particular engine. It is a graph of how much air (Usually in lbs/min) a turbo can flow at a given P/R. P/R or Pressure ratio is a measurement of boost, same a BAR, it is the absolute pressure the engine is getting from the turbo divided by the air pressure the compressor wheel is seeing. In a perfect world it would be atmospheric pressure which at sea level the standard is 14.7psi. It will always be less when running an air filter, which you should to protect the turbo from road debris. Boost is the pressure above atmosphere the engine is seeing and can be found by P/R times 14.7 - 14.7. example, 1.5 p/r x 14.7= 22.05 -14.7 = 7.35psi of boost.

General rules of forced induction, that give close /approximate results (there are long equations you can do, to get a more accurate result).

1. To find out how much boost you would need, Take the HP level you want and divide it by the horsepower the engine currently has without boost and that is the "approximate" pressure ratio needed to make that much power. For example: If you have a 300hp V8 and want 450hp, 450/300 = 1.5 or a 1.5 P/R. I say approximate as it will almost always take slightly more boost( usually 1-2psi more) to reach that level do to turbo/intercooler efficiency.

2. Another excepted standard is that it takes 10lbs/min of air for every 100hp, so the v8 in the example would need a turbo (if only 1 is used) that can supply 45lbs/min of air at a P/R of 1. 5/1.6. to make the 450hp.