The internal combustion engine design has been evolving for centuries now, to reach higher levels of efficiency and greater power output. Many technological innovations have come into play to make fuel efficient and computer-controlled engines possible, that provide phenomenal power by optimizing operation. Two of the technologies that have improved the power output of internal combustion engines are superchargers and turbochargers. While both are different in design, their working is based on the same basic principle.
Let me provide a brief overview of engine functioning, which will help you understand the working of both. A car engine is driven by the pressurized combustion of gasoline or diesel as fuel. The explosive combustion of fuel creates an oscillatory motion of the piston, which is then converted into torque, through rotation of the crankshaft.
The engine breathes in air through an inlet valve to make combustion possible. To derive maximum power from every combustion stroke of the engine cycle, the right proportion of air is necessary. More air an engine can breathe, more clean is the combustion and better is the power output of an engine.
Though superchargers and turbochargers are structurally different, their function is identical. Both these devices increase the power output of an engine, by supplying compressed air through each intake stroke. If you recall some basic physics, you will know that density is mass divided by volume. So an increase in density means that more amount of air is packed in lesser volume. This in turn means that the engine is breathing in more air, during every engine cycle, leading to higher engine power output.
How are They Different?
There are more than one ways in which compressed air can be supplied to an engine to boost its performance. Superchargers and turbochargers achieve air compression and engine power boost through different mechanisms, which we discuss in the following lines.
The main point of difference is the power source which drives their air compressors. While a supercharger's air compressor is powered by the engine torque itself (via a belt), a turbocharger uses the engine exhaust to power its air compression mechanism. The supercharger is driven by a belt, which is similar to the ones used for driving alternators. On the other hand, a turbocharger's air compressor is driven by the torque provided to a connected turbine, by the engine exhaust stream.
Difference in Efficiency Level
A difference in functional efficiency of the two technologies arises because of the different power sources they have. A turbocharger is much more efficient, compared to a supercharger, as it utilizes the otherwise wasted energy that is contained in the exhaust stream, by virtue of its momentum. However, it does cause a certain amount of back pressure (due to its connection with the exhaust), which can affect engine functioning and cause a lag. On the other hand, the turbocharger uses engine torque output, bringing down efficiency, though it doesn't cause a back-pressure problem.
To conclude, the difference between the two lies in the way they both are powered, resulting into a substantial difference in performance. These technologies have made the functioning of high speed sports cars possible. As discussed before, if you are looking for efficiency, turbochargers are the right choice as they make better use of energy. Compared to this, a supercharger is fractionally less efficient.