Stall Speed
The maximum engine RPM that can be achieved in an automatic transmission when the output shaft is locked and the throttle is wide open.
Stall speed is a performance characteristic of a torque converter in an automatic transmission. It represents the maximum RPM the engine can reach when the transmission is in gear, the brakes are fully applied (locking the wheels), and the throttle is held wide open. At this point, the converter's impeller is spinning at engine speed, but the turbine is stationary, causing the fluid to shear at its maximum rate.
A vehicle's stall speed is determined by the size and angle of the converter's internal stator and fins. A standard passenger car typically has a low stall speed (1,500 to 2,000 RPM) for smooth, fuel-efficient acceleration, while high-performance or heavy towing vehicles may use a high-stall converter (2,500 to 4,000+ RPM) to let the engine reach its power band before launching.
Technicians perform a 'stall test' to diagnose transmission and torque converter health. If the engine RPM rises significantly higher than the specified stall speed, it indicates that the transmission clutches or bands are slipping. If the RPM fails to reach the specified stall speed, it suggests a lack of engine power or a failed torque converter stator one-way clutch.