What does a torque converter do?
NASA defines a torque converter as a device for changing the torque speed or mechanical advantage between an input shaft and an output shaft. Automotive torque converters connect the engine to the automatic transmission. The converter housing bolts to the flexplate and spins at the same speed as the engine. On the output side, the torque converter's turbine is attached to the transmission's input shaft. Inside, the converter has a stator assembly and fluid. The stator redirects fluid flow to create torque multiplication for increased low-speed acceleration. Most converters multiply torque by a ratio of at least 2:1, improving vehicle acceleration substantially. A vehicle's engine must be able to connect and disconnect from the differential, so it can stop moving while the engine is running and the transmission is in gear. In the case of an automatic transmission, it is the torque converter that performs this connect/disconnect function. By slipping internally, the torque converter allows the car to idle while it's in gear.