Calculate torque converter stall speed from the K-factor and engine torque, or find the K-factor, torque at stall, or new stall after a torque change.

GM 298mm code letters give a nominal K-factor. Use the K-factor from your converter maker if you have it.

Torque the engine makes at the stall RPM, which can be lower than its peak torque.

Optional settings

K Factor Formula

The following formula is used to calculate the k-factor (capacity factor) of a torque converter.

K = (RPM) / (√(T))
  • Where K is the k-factor (capacity factor) of the torque converter
  • RPM is the converter’s stall RPM
  • T is the engine torque (input torque) at stall (lb-ft)

To calculate the k-factor of a torque converter, divide the stall RPM by the square root of the torque output.

Stall Converter Definition

A stall converter (high-stall torque converter) is a torque converter used in an automatic transmission that is designed for a particular stall speed. At stall (when the turbine is held), the converter produces its maximum torque multiplication.

Example Problem

How to calculate k-factor?

  1. First, determine the converter’s stall RPM.

    For this example, the stall RPM of the torque converter is found to be 4000 RPM.

  2. Next, determine the maximum engine torque output.

    For this example, the engine can output a maximum of 400 lb-ft of torque.

  3. Finally, calculate the k factor.

    Using the formula above, the k factor is found to be:
    K = RPM / Sqrt (T)
    K = 4000 / Sqrt (400)
    K = 200