How Does a Torque Converter Work


Instead of the clutch used in manual transmissions, the torque converter is responsible for transferring and amplifying engine power to the ground in automatic gearboxes. If we were to dissect a converter, we would find three primary parts: the impeller, the stator, and the turbine. The impeller, or impeller pump, is situated on the transmission side and rotates at engine speed as rpm increases, fluid flow within the converter increases. This power is conveyed using vanes and fins that direct the flow towards the turbine, which is secured to the flexplate. The stator is located between the impeller and turbine. It operates as a type of one-way clutch that reroutes fluid and multiplies torque production. When the fluid flow is strong enough, it begins to spin the turbine, which is splined to the transmission’s input shaft. Each converter’s properties are determined by its diameter, number and form of fins, and stator design.

How Does a Torque Converter Work

Stall Speed of a Torque Converter

The stall speed is the maximum engine speed that can be reached with the brakes locked and the gearbox in gear before the drive wheels begin to turn. The stall speed is merely a measurement of the converter’s performance level. The provided range indicates what to expect from the converter. If a 2700-3000 is selected, depending on the vehicle’s setup, you should be able to footbrake stall the converter at about 2700 rpm. This should provide anywhere from 500 to 1,500 more rpm to launch the vehicle from a dead stop compared to the original converter, resulting in a noticeable boost in the vehicle’s acceleration capacity.

Selecting a Torque Converter

It is crucial to select the correct converter and stall speed for your vehicle, not just on the street but also on the racetrack. The proper decision can be the difference between victory and defeat; between a car that performs to its full extent and one that falls short of its potential. Choosing the proper torque converter for your application might be challenging, but there are some basic rules you can adhere to. Consider your power curve and torque output as two of the most important factors. A stall speed range of 2,200 to 2,700 rpm is intended to accommodate a variety of engine characteristics with distinct power curves. Ideally, you want the stall to occur near the engine’s maximum torque. Generally, engines with greater low-end torque will have a higher stall speed. The same converter will stall at a lower rpm while driving an engine with less torque at a higher rpm.

Consider also the resistance you will encounter against the engine. A heavier vehicle with large-diameter tires creates additional resistance. In general, the higher the stall rpm is, the greater the resistance. Similar concepts apply to gear ratios. A heavier automobile with taller gears and larger tires will have a greater stall rpm than a lighter automobile with shorter gears and smaller tires. In conclusion, the characteristics are as follows: vehicle weight, engine displacement, compression ratio, cam profile, rear end gear ratio; tire diameter, the type of fuel system, and the model and year of the gearbox.