Because proper combustion in an engine requires a precise air-to-fuel ratio of 14:1, pumping more gas into an engine to increase its power output would be useless without a much larger supply of air to the combustion chambers. An engine simply requires much more air than fuel. But, rather than building a larger, heavier engine to hold all this additional air, turbochargers condense incoming air so it fits in the relatively small volume of conventional engines. In a turbo, this compression is achieved through a system of rotating gears or fans driven passively by exhaust gases. If the air compression is driven by the engine's crankshaft the turbo device is called a supercharger. There are many designs of turbos and superchargers, though they all operate on the same simple principle. All must compress air to produce the pressure differential that forces additional air into the engine.
Before turbos, oxygen was the limiting factor in the power of engines. The element is a crucial ingredient in combustion, and by increasing its availability to an engine's internal combustion chambers, where it is mixed with gasoline for the explosive reaction that powers the engine, the process can be more efficient. Turbos force air into the combustion chamber at pressures greater than the external atmosphere, and this compression of the air makes more oxygen available for combustion, meaning engines do not necessarily have to be built larger to be more powerful. This, in turn, translates into lighter cars and increased fuel efficiency. Of course, this principle can applied in any engine, and, in fact, turbos are essential in airplanes, which are able to fly at higher altitudes where oxygen is less abundant because of their increased efficiency.
An additional feature that increases the efficiency of the turbo is the inter-cooler, sometimes called a turbo-cooler, which lowers the temperature of the air as it enters the intake manifold of the engine. Because compressing air increases its temperature, potential energy for the combustion stroke is lost to heat. Like a radiator, a turbo-cooler uses cold air or water to reduce the temperature of the compressed air before it reaches the engine. This provides peak efficiency by increasing the difference between the air's temperature before and after combustion, resulting in greater power. Without the inter-cooler, the risk of heat damage, excessive wear or an uncontrolled explosion in the engine increases.