Turbochargers are fans powered by gasses from the car's exhaust system. They allow more compressed air to go into the cylinder. That allows for a higher compressions ratio (just like direct fuel injection), and therefore, more efficient combustion. Think of a turbocharger as direct injection for the air part of an engine's air/fuel mixture.
While using a turbocharger allows performance cars to generate even more power, putting them on a smaller engine allows them to do the same work as a bigger engine -- and that saves fuel. In 2011, Ford added a turbocharged V-6 engine to its line of engines for its F-150 trucks. Called EcoBoost engines, they prove that you don't need a V-8 in a pickup. With a turbocharger, the EcoBoost engine in the 2011 F-150 makes 365 horsepower, 420 pound-feet of torque and can tow up to 11,300 pounds (5,126 kilograms). By comparison, the base V-8 in the F-150 makes 360 horsepower and 380 pound-feet of torque. The EcoBoost V-6 in the F-150 not only makes more power, it also gets better fuel economy than the V-8. In two-wheel drive, the EPA says it gets 16/22 miles per gallon (6.8/9.4 kilometers per liter) city/highway, while the base V-8 gets 15/21 miles per gallon (6.4/8.9 kilometers per liter) city/highway.