All advertised stall speed ratings of all torque converters are nominal ratings regardless of the manufacturer or converter design. These advertised ratings are not indicative of the actual stall characteristics of a torque converter. Advertised stall speed ratings are published simply as a general guideline to help in the selection of the correct torque converter for a customer’s application. A torque converter will provide a range of stall speeds based on the amount of load that is placed on the torque converter. Many factors influence torque converter stall speed including; output torque of the engine, vehicle weight, rear axle ratio, rear tire height, torque converter diameter, impeller fin angle design, stator design, impeller-to-turbine clearance, stator-to-impeller clearance, stator-to-turbine clearance, and brake bias.
When considering torque output of the engine, you must not only consider peak torque but average torque, and must consider all components and design characteristics of an engine that will influence torque production. Several key factors to consider in engine design that will have a dramatic impact on torque production and the overall shape of the torque curve include but are not limited to; stroke length, static and dynamic compression ratios, camshaft specifications, cylinder head intake runner volume, intake manifold design, header primary tube size and length, etc. Something as seemingly simple as an incorrectly tuned idle and/or part throttle circuit in a carburetor or incorrectly tuned ignition timing can have a dramatic negative impact on the stall speed characteristics of a torque converter.