S (stall point): In this particular place the turbine velocity is zero plus the impeller is rotating; the efficiency while in the stall stage is minimum, about 50%, which suggests that half of the power coming within the motor is dropped by way of friction and dissipated as warmth; at https://torqueconverterclutch75296.mdkblog.com/40099798/torque-converter-clutch-fundamentals-explained