View Thread: Continuing Automotive Education Part 2

What a torque converter actually does courtesy of Summit Racing.

At the most basic level, a torque converter connects the engine to the automatic transmission, much like a clutch connects an engine to a manual transmission. The converter housing bolts onto the motor's flexplate (also known as the flywheel), and the housing spins right along with the motor. On the output side, the torque converter's turbine is attached to the transmission's input shaft. Inside the torque converter is a stator assembly. It redirects fluid flow, resulting in torque multiplication and torque multiplication is what allows a converter to provide better low-speed acceleration. Most torque converters today will multiply torque by a ratio of at least 2 to 1. For example, if your motor is making 250 lbs.-ft. of torque and your converter is multiplying it by a factor of two, then the transmission will see 500 lbs.-ft. of torque. This can improve a car or truck's acceleration capability substantially. NASA defines a torque converter as a device for changing the torque speed or mechanical advantage between an input shaft and an output shaft. The goal for automotive enthusiasts, clearly, is to gain a mechanical advantage. The torque converter also serves another extremely important function in a car or truck. A vehicle's engine must be able to connect and disconnect from the differential, so the car or truck can stop moving (i.e., turning the drive wheels) while the engine is still 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 (again, like a clutch in a manual transmission). By slipping internally, the torque converter allows the car to idle while it's in gear.