ANSWERS: 1
  • A torque converter's main job is to allow the engine to idle below a certain rpm without engaging the transmission. The rpm at which this happens is called the "stall speed" and can have a huge impact on the vehicle's performance and character.

    Converter Function

    A converter uses a turbine attached the engine's crankshaft to push fluid through a matching impeller on the transmission. The rpm at which the engine-side turbine overwhelms the transmission impeller's ability to pass fluid without moving is the stall speed.

    Stall Speed Tuning

    Stall speed is usually increased by decreasing the converter diameter, so that the engine must rev higher to pass enough fluid to engage the transmission.

    Stall Speed Effects

    Since engines make more power with higher rpm, performance applications often utilize a high stall converter to engage the transmission later.

    High-Stall Overheating

    A converter with an excessively high stall speed can cause fluid overheating, poor power transfer and poor fuel economy.

    Stall Speed Testing

    Stall speed can be determined by power-braking (applying the gas and brake at the same time from a stop.) The rpm at which the engine overpowers the brakes or that at which it stalls under load is the stall speed.

    Source:

    Rod and Custom Magazine: Understanding Torque Converters

    Car Craft Magazine: What's up with Stall?

    Chevy High Performance Magazine: TCI transmission and Torque Converter Technology Insights.

    Resource:

    youtube.com: Testing Converter Stall Speed (Video)

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