What is Torque Converter Slip?

Torque converter slip is the difference between the rotational speed of the engine (input) and the rotational speed of the transmission (output) inside the torque converter. In an automatic transmission vehicle, the torque converter acts as a fluid coupling. Unless you have a lock-up converter engaged, there is always a slight difference in speed between the pump (connected to the engine) and the turbine (connected to the transmission).

How to Use the Calculator

To calculate your converter slip, you need four key pieces of data from a drag strip pass or a data log: your engine RPM at a specific point, your rear-end gear ratio, the actual diameter of your rear tires (under load), and your actual vehicle speed (MPH) at that same moment. Simply enter these values into the fields above and click calculate. The tool will provide a percentage representing the efficiency loss through the converter.

Interpreting Your Results

For high-performance drag racing and street-strip applications, a "tight" or efficient torque converter typically shows between 5% and 10% slip at the finish line (Wide Open Throttle). If your slip is above 12-15%, your converter may be too "loose" for your setup, leading to excessive heat and lost MPH. Conversely, if your slip is 0%, you likely have a lock-up converter engaged. If the calculator shows a negative number, it usually indicates tire growth at high speeds or an inaccurate tachometer/speedometer reading.

Frequently Asked Questions

Does tire growth affect the calculation? Yes. At high speeds, bias-ply tires can expand, effectively increasing the tire diameter. This will make your slip appear lower than it actually is. Why is slip important? Higher slip creates more heat, which is the primary enemy of automatic transmissions. Maintaining an optimal slip percentage ensures that you are putting the maximum amount of power to the ground while keeping transmission temperatures under control.