If you have a Prius, one of the reasons you bought it is probably the fuel economy. The EPA gives the 2012 Prius a 50 miles per gallon (21.3 kilometers per liter) combined rating for city and highway driving, making it one of the most fuel-efficient cars on the market. The hybrid powertrain is a major reason for this, but it's not the only reason. The aerodynamic design helps a lot too. And so does the beltless engine. By taking power-generation duties away from the internal combustion engine, reducing the energy inefficiencies that auto engineers refer to as parasitic losses, a beltless engine consumes less gas. And because a beltless engine loses less energy to friction than the older kind, it generates power more efficiently.