Your basic gasoline car engine isn't all that efficient. Of all the chemical energy in gasoline, only about 15 percent gets converted into the mechanical energy that actually moves the car. The EPA says over 17 percent of the energy is lost as the engine idles, and a whopping 62 percent is lost in the engine due to heat and friction.
Modern engines have a number of technologies in place to make them more efficient. For example, direct injection technology, which mixes the fuel and the air before they're put into the cylinder, can improve engine efficiency by 12 percent because the fuel burns more efficiently [source: U.S. Department of Energy]. Turbochargers, which use compressed air from the car's exhaust system, compress the air that's used in the combustion cycle. The compressed air leads to more efficient combustion. Variable-valve timing and cylinder deactivation are technologies that allow the engine to use only the fuel it needs, increasing efficiency.
There's a common misconception that efficient engines are underpowered engines. Keep reading to learn how modern engines out-muscle their older counterparts.