An internal combustion engine is a complex air pump. It produces torque (or twisting force) within a specific RPM range based on the configuration of the engine and the cam profile. Most overhead valve pushrod engines turn about 2500 rpm to produce their peak torque. Often by 4500 rpm they are producing so little torque that continued increases in engine speed produce no torque increases.
Torque peak on overhead camshaft engines usually occurs at higher RPM within a smaller range of engine-speed.
Manual transaxles allow the driver to manipulate torque by manually engaging the transmission through a clutch. Manipulating the torque through the clutch allows for smooth operation from a standing start.
Manual transaxles change the ratio between the rotating speeds of the engine and the wheels by the use of gear ratios. In today's automobiles, five and six speed transaxles are most common. The lower gear ratios in first and second gear allow engine power to be multiplied to the wheels during low speed acceleration.
The clutch friction disc is made from a variety of materials. The disc can also include metallic particles impregnated into the disc to increase torque transfer. The center of the disc is splined to mesh with the transaxle input-shaft.
The clutch pressure plate is bolted to the engine flywheel and incorporates a series of springs (diaphragm or Borg & Beck style) that provide pressure to engage the clutch. The friction disc is pressed between the flywheel and presure plate until complete union between the three components is accomplished when the clutch pedal is released.
There are three gear-shafts in a manual transaxle; the input shaft, the mainshaft, and the countershaft. Torque transfer enters the transaxle from the input shaft. The input shaft transfers the torque to the countershaft that, depending on gear selection multiplies the torque through varying ratios. The gear selection is then transferred to the mainshaft that carries the torque (power) to the final drive where it is delivered to the axles to create forward-thrust.