In addition, the compact car will produce 45 percent fewer emissions of carbon dioxide. As a general rule, the larger the engine, the more fuel it will consume. A 2.5 litre engine burns over one litre of gasoline per hour while idling. A 5-litre engine burns twice as much about two and a half litres per hour. 3.3 Transmission and Drivetrain Transmissions that offer a wider range of gear choices will almost always deliver improved fuel economy by decreasing the engine speed while maintaining the same vehicle speed.
Manual transmissions are usually more efficient than automatic transmissions.
Four-wheel drivetrains usually increase fuel consumption. 3.4 Shape Pickup trucks and vans generate significant aerodynamic drag because of their blocky shape and high profile. In the case of pickup trucks, a simple way to improve aerodynamics is to cover the cargo box with a fitted tarp or fitted fibreglass cap. Opening a sunroof or windows at highway speeds increases aerodynamic drag and fuel consumption. Tinted glass keeps cars cooler.