What factors detract from cars with high fuel efficiency?

What factors detract from cars with high fuel efficiency?
Cars with high full economy are usually under powered. The car's computer limits the amount of gas the engine can get by changing the amount of time the fuel injectors spray. They do this also to reduce emissions.

With older cars, what you did with your right foot, the engine did, because there was a physical connection between the gas pedal and the throttle. Today's cars use a system called "drive by wire," which means that when you hit the gas, your sending an electrical signal to the computer, which sends a signal to the throttle plate to open. This system allows the computer to monitor and control the engine, but it causes a delay from the time you hit the pedal and the time the engine revs.