How to Choose a Stall Converter

by Francis Walsh

Making power starts at the engine and ends at the wheels. How you get the power from under the hood to the street depends on which torque converter you place in between the engine and the transmission. How to choose a stall converter has everything to do with the type of driving you do and the performance your engine can deliver. If you make the wrong stall converter decision, getting an engine package to work at peak performance will be futile.

Before selecting a torque converter, determine the driving conditions of the engine. The type of ride and the performance expected determine the choice of a torque converter for street use. Late-model daily drivers require the engine to utilize its horsepower at a lower rpm that needs a lower stall, or lock up of the torque converter's impeller to the turbine. This type of stall converter will "stall" or lock up in the 1,500 to 1,700 rpm range, which limits performance but adds the smooth drivability every daily driver needs when getting around town.

Gain performance from a race engine by increasing the stall of the torque converter. Increasing the torque converter stall will make the engine rev higher before the torque converter locks up with the turbine. This creates more engine force to be exerted into the transmission before the transmission returns the energy to the wheels. Consider a car that begins to rolls only when the engine has built up enough rpm, and the rpm is at 3,000 instead of 1,500. This type of launch is designed for race-ready vehicles and not street-legal cruisers. The higher stall converter will run rough at idle and will experience a lot of torque converter slippage if driven on the street.

Measure the tire height and rear gear ratio to pinpoint the type of stall converter that will work best for a street-ready, or drag-race machine. For the experienced sportsman, the factors that play most heavily on the selection of a proper stall torque converter are launch, cruising speed, gear ratio and tire height. All these components must come together within the correct rpm range to save the torque converter from damage. Mismatched transmissions and torque converters will result in costly damage if they are combined under the wrong driving conditions.

Select a torque converter size that is correct for your application to combine the right stall speed and rpm with the type of driving you plan to do after the torque converter is installed. Smaller diameter torque converters normally have higher stall speeds and rpm ranges and are used for high-performance applications. Use the information you have on the vehicle and the type of performance you expect to select the correct stall torque converter.

Tip

  • check Use an existing torque converter to determine the vehicle's current foot-brake stall and flash stall. Foot-brake stall is the rpm at which a vehicle moves forward while the brakes are depressed fully and the accelerator depressed completely. Flash stall is the rpm at which a vehicle moves forward at full acceleration without the brakes being applied. Use this information to increase or decrease the stall for your performance expectations.

Warning

  • close Torque converters under extreme stress can balloon during launch. This torque converter ballooning can result in permanent damage to both the converter and the transmission. Do not mismatch the engine's power with the torque converter's stall speed to create a condition that can result in bodily injury and internal engine damage. Expectations should always be kept in check when advancing performance engine parts for the biggest gains.

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About the Author

Francis Walsh has been working as a freelance writer since 2003. He has contributed to websites such as Shave, Autogeek and Torque & Chromeas, as well as provided content for private clients. Walsh has worked as a performance part-packer and classic car show promoter, now serving as crew chief for Nitrousfitz Racing.