Skip to content
What does a Torque Converter Do?

What does a Torque Converter Do?

What part does a torque converter play in a transmission?

A transmission is a significant component of a vehicle as it converts rotational motion from the engine into linear motion.

cutout image of automatic transmission There are two basic types of transmissions: the standard shift manual transmission and the automatic transmission. The manual transmission consists of gears, sliders, synchronizers, and fluid. An automatic transmission also has several parts, including a torque converter, gears, drum assembly, clutches, bands,and fluid.
In a few words, the transmission is responsible for converting the power generated by the engine into forward movement. This process involves many different components, which must all function properly for the carto move.
Because transmissions are complicated, we will focus on the basics of automatic transmission torque converters in this article.

What's a Torque Converter

The torque converter is one of the first components of the transmission. It is located between the engine and the transmission and acts as a fluid coupling. It allows the engine to spin the pump inside the transmission to move fluid, which keeps the transmission working properly.

Because it is made to transfer the engine's power, a torque converter allows the tires to move. For this to be successful, the motor spins the converter to move the fluid inside the transmission. Doing so directs fluid within to drive the car forward.

There are many pieces inside the torque converter to make this happen. Within the converter, you have the pump hub, impeller, stator, one-way clutch, turbine, bearing, and cover. For lock up applications, which are discussed later in this article, there is an additional element of having clutches within the torque converter.

Torque converters are very tunable and can be built for every application available. To transfer the fluid in a way that is optimal for your application, you can modify each part within the converter.

torque converter rendering of fluid moving inside

The stator and the turbine perform together for the car to either move or not. As the throttle is applied and the engine's RPMs go up, it spins the torque converter, which moves fluid through the stator to the turbine. The fluid movement transfers power from the engine to the transmission.

When the motor is running but the vehicle is stopped, the one-way clutch stops the stator, which prevents the impeller from sending fluid through to the turbine. Since it is a fluid transfer, there is about a 15% loss from the engine to the rear tires in this type of torque converter.

Lock up Converters

Lock up torque converters have clutches within the converter itself. These clutches have friction materials built into them to apply pressure to lock up the converter and eliminate slippage. Standard none lock up converters generally lose about 15% of the power from the engine to the rear wheels.

The Original Equipment Manufacturers (OEMs) started creating lock up torque converters to maximize power and efficiency, thus giving modern vehicles better gas mileage as well.

For years the OEMs have had twin disk clutches in their torque converters. Now, many aftermarket companies have three to five clutches in the lock up converters they sell. These torque converters have one to five clutches built into them.

Lock up converters work primarily the same way as your standard torque converters, except that as the turbine spins, it applies pressure to the clutches. As this happens, the applied pressure virtually locks the impeller and turbine together. At this point, all slippage is eliminated. The engine and transmission are now in a 1:1 ratio.

The more clutches, the less slip there is within the torque converter. These clutches can be made of many different types of friction materials, such as Kevlar-based material, carbon fiber-based material, or reinforced organic cellulose.

How is the converter stall speed determined?

Torque Converter from G Force

The stall speed is the maximum amount of impeller RPM without the turbine moving. When you buy a converter, the stall speed is an advertised number. The advertised stall speed for a converter will not provide that stall speed for every application. A 1500 stall speed converter may stall at 1200 for one application but 1800 for another application. Many variables cause the stall speed.

Converters are load-sensitive parts, and the stall speed is not a fixed number. Tires size, cubic inch, torque output of the engine, the weight of the vehicle, rear end gear, and transmission gearing can all change the stall speed of a converter.
Basically, there are three ways to determine the stall speed of your torque converter.

The first way is foot brake stall speed. That is holding your foot on the brake while hitting the accelerator. The amount of RPM you can achieve before overpowering the brakes is where the converter will stall. Yet, this is not a very precise way to determine the stall speed.

The second is flash stall speed. Best way to check this is in high gear at low speed and go full throttle while watching a tachometer. When you instantly hit the throttle, the RPM will max out at the stall speed.

Finally, the last way to figure out the stall speed is to physically lock the rear wheels so they can't move or use a transmission brake. This way is the most accurate, but it is more difficult because you must do it on stands and remove the low-speed rev limiter. This method is most commonly used in drag race applications.

G Force Performance Products Torque Converters for 4L80E Transmissions

G Force Performance Products offers three different lock up style torque converters for the GM 4L80E transmission.

Buy a G Force Torque Converter

The first offering is part number GF-80S1200. It is a GM stamped steel core converter featuring a carbon fiber clutch single disk clutch for full lock up. This converter is rated at 600 horsepower and 750-foot pounds of torque. It will stall in the 1200 RPM range.

The second of the G Force torque converters is part number GF-80B1200 which has a billet steel cover converter for more strength. The more substantial construction of this converter allows it to be rated for 1000 horsepower and 800-foot pounds of torque. It also features a single carbon fiber clutch disk for full lock up and stalls at around 1200 RPMs.

The final offering is part number GF-80B31200 which also has the billet steel cover for added strength. This converter features three carbon fiber disks to achieve full lock up. It's rated for 1100 horsepower and 1500-foot pounds of torque. The stall range for this converter is also in the 1200 RPM range.
Keep in mind that these converters may stall differently. The real-life range is from about 1000 RPMs to 2000 RPMs depending on the combination. These three torque converters are intended for a Cummins engine swap into a GM truck using the GM 4L80E transmission.

You may find details about the G Force Torque Converters for 4L80E on the individual product pages.

G Force also offers two Cummins to Chevy Transmission Adapter Swap Kits for the 4L80E:

Cummins to 4L80E Swap Kit

1989-2002 Cummins to TH400/4L80E | GF-C-S
2003-2017 Cummins to TH400, 4L80E | GF-C-SL

You may be interested in the information G Force put together regarding A Diesel Cummins Conversion or Cummins Swap.

Questions about G Force Torque Converters?

Live Chat or give us a call at 330-753-5300

Next article Why do you need a Transmission Cross Member