Driver Input

• The automatic transmission manages functions without much driver input. The driver can concentrate on steering and braking instead of shifting gears to match road conditions. This is helpful in city traffic.
  
  

Fuel Economy

• The manual transmission is generally the most efficient transmission. It uses a mechanical clutch to transfer engine torque to the drive wheels. Manual transmissions do not require a torque converter, saving weight. Gear ratios in the manual are achieved when a series of gears lock and unlock to the transmission's output shaft. The automatic transmission transfers power through a torque converter. There is a 3- to 4-mile-per-gallon sacrifice in this process. The same set of gears produce the gear ratios needed to move the vehicle.
  
  

Power Consumption

• Manual transmissions require very little engine power and do not require the hydraulics for clutch engagement. Their power consumption comes from the drag of the gear train being submerged in the transmission lubrication. Automatic transmission power consumption comes from the pressurized fluid in the torque converter. The energized fluid is required for operation of the clutch sytems to determine proper shifts.
  
  

Advances in Automatic Transmission Efficiency

• The efficiency of the automatic transmission has improved with the introduction of the lockup torque converter. When engaged, energy loss is reduced. Computers add more efficiency because they download the shift logic information, which is stored in the transmission's valve body. Some automatics can learn a driver's style of driving.
  
  

Turbocharged Applications

• The automatic transmission can be more efficient than a manual when it is coupled with a turbocharged diesel engine. With a manual, turbo boost is lost between gear changes and the boost pressure has to build up again. The automatic can shift faster than is humanly possible. This reduces the loss of turbo boost and the vehicle can accelerate faster than the same model vehicle with a manual transmission.
  
  

Heavy-Duty Use

• Heavy-duty trucks, buses, motor homes and fire engines used to be exclusively equipped with manual transmissions. The modern heavy-duty automatic transmission is designed for enhanced performance and can provide more than 1,700 lbs./ft. of torque for diesel engines producing from 200 to 300 horsepower.