Torque Converters

Is your car sluggish off the line, or does your automatic transmission need to handle more torque after tuning? The torque converter sits between the engine and the transmission and determines how power is transferred. Here you'll find replacement units and heavy-duty torque converters for both daily driving and more demanding projects.

What does stall speed mean?

Stall speed is the RPM the engine can reach before the torque converter really starts pulling the car forward. A higher stall can let the engine get into its power band faster off the line, but it can also cause more slip, more heat in the transmission fluid and a looser feel in traffic. From FTI Performance, the models in this category are available, for example, with stall from 3000 to 4000 RPM.

How to choose a torque converter

• Transmission type: The unit must match the specific transmission, e.g. 4L60E, 6L80E, 48RE, 545RFE or 5R110, and often also the engine's mounting interface.
• Stall: The choice depends on the engine's torque curve, the vehicle's weight, the gearing and the intended use – not just on how hard the car should pull.
• Diameter: Specifications show e.g. 9.5" and 11"; a smaller diameter typically gives a higher stall.
• Lockup and construction: The lockup clutch locks the engine and transmission together at steady speeds and can reduce slip and heat. The number of clutch discs and a billet cover can affect how much torque the unit can handle, e.g. in diesel projects with ATS Diesel. Other brands in the category are BD Diesel, Pure Drivetrain Solutions and S&S Cycle.

Installation and interaction with the transmission

The torque converter must be fully engaged with the transmission pump before the transmission is bolted to the engine. If the transmission is worn, it may be worth combining it with a transmission rebuild kit or a complete automatic transmission. With electronically controlled transmissions, lockup and shift patterns may require adjustment via a transmission control module.

Frequently asked questions

Which stall speed should I choose?

It depends on the engine's torque curve, camshaft, vehicle weight, rear axle ratio and use. Too high a stall can cause unnecessary slip and heat in daily driving, while too low a stall can leave the engine working below its power band off the line.

Can a torque converter cause the transmission fluid to overheat?

Yes, more slip with a high stall or infrequently engaged lockup can increase the transmission fluid temperature. For hard use, an additional transmission cooler may be relevant, but the need depends on the car, weight and driving style.

Should the torque converter be replaced when the transmission is rebuilt?

It is often recommended, because debris from a failed transmission can collect in the old torque converter and be carried into the rebuilt unit. The transmission cooler and lines should also be cleaned or replaced.