The engine range was initially composed of only turbocharged three cylinder motors. Originally, the base petrol engine had 599 cc, but displacement was increased to 698 cc along with the restyling. It was available in 37 kW (50 hp) or 45 kW (61 hp) variants. The turbodiesel engine has 799 cc displacement with 30 kW (40 hp). The new 999 cc version (2007 onwards) comprises normally aspirated (NA) and turbo versions. The NA 999 cc engine has 11.4:1 compression ratio and premium fuel (95+ RON) is recommended. It is rated at 71hp and is also the only engine currently offered in the US. The US NA 999cc engine has a 10:1 compression ratio and premium fuel (91 Octane) is recommended. German tuner company Brabus, in a joint venture with smart, has developed a version with 72kw (98hp) and 140Nm torque, available in Europe only at this time.
Although a manual transmission is offered, there is no clutch pedal. Instead, input from floor-mounted shifter (via a stick) or optional steering wheel-mounted paddles is fed to a servo-operated clutch to shift the sequential automated gearbox. Using European EEC standards, the smart has mpg averages of 4.7 L/100 km (50 mpg U.S.) for the gasoline model and 3.4 L/100 km (69.2 mpg U.S.) for the diesel. However, under new EPA guidelines the U.S. gasoline version is rated lower, at 36mpg combined.Source: Wikipedia.