Because of the specific angle with the stator blades, the fluid flows back in a slower rate, which multiplies the torque. In a torque converter you can find at least 3 rotating elements: the impeller, which can be mechanically driven with the key mover; the turbine, which drives the load; https://torqueconverterclutch58136.bloggadores.com/33182997/a-review-of-torque-converter-clutch