Mustang S197 Torque Converter - Loose As A Goose - Tech

Two other important parts of the torque converter are the stator and the sprag. The stator has been likened to the brain of the converter, and its job is to change the flow of transmission fluid between the turbine and the pump. It's also what makes the converter as a whole a torque con-verter, or multiplier, and not simply a fluid-coupling device. The operation of the stator is directly linked to the operation of the sprag. The sprag is a one-way mechanical clutch that fits inside of the stator. The stator is related to the sprag in that the sprag must work correctly for the stator to do its job. To do this, the stator must hold the sprag in the proper position when the converter is in stall mode. Stall mode is when the turbine speed is slow in relation to the impeller-pump speed. In addition, the stator must allow the sprag to spin with the rest of the converter after the turbine speed nears the speed of the impeller pump.

The sprag is important in that it is the part that multiplies the torque coming from the engine to get the vehicle moving. If the sprag breaks, the car won't move-it's as simple as that. Torque multiplication is done both in stall mode as well as when the vehicle is accelerating. This torque multiplication is what gets an automatic car to move from a standing start. Once the converter has reached a 1:1 ratio, or full lockup, the torque multiplication decreases rapidly. This is because the car is already moving and doesn't need that extra grunt to get going. Additionally, the turbine and pump are at the same speed, thus resulting in the power from the engine being transferred down the line in a direct manner.

The last part of the converter is the impeller pump. This is on the half of the converter facing the transmission. Inside the pump are a series of aforementioned fins, which drive the transmission fluid inside of the converter into the turbine. The size of the converter, the size of the pump, and the number and shape of the pump's fins are what gives each torque converter its unique characteristics. Converters generally range from full racing units in the 7-, 8-, 9-inch range, up to 10-, 11-, and 12-inch converters from the OEM. Larger converters have more internal area so the fluid stays cooler and there is less slip or stall. Smaller converters generally will have a higher stall speed, and that's why they're used in racing. Also, with less fluid moving through them, heat can build quickly.

Now that we have the basics out of the way, let's turn to the differences between the stock torque converter and the new TCI Super Street-fighter converter that we installed. The TCI piece is made specifically for the 5R55S five-speed automatic transmission found in the new S197 Mustangs. According to Tony Akins of TCI, there are a myriad of differences between the stock converter and the TCI one.

"For starters, the stock converter is 12 inches in diameter, while the Super Streetfighter is 10 inches," Akins says. "Internally, our converter has a billet stator and furnace-brazed fins that are tack-welded for durability. The stock converter has a cast-aluminum sprag, while ours is a billet piece. Also, our lockup material consists of different material than the stock converter. All of our converters utilize much of the same equipment we use in our 2,000hp Powerglide converters."

All of the internal modifications add up to a converter with characteristics that are much different than the stock piece. "The sprag that we use actually reduces slippage anywhere from 7 to 10 percent," Akins says. "All of this translates into a converter that has less rotating weight, as well as more stall speed. A stock 5R55S converter will have a stall speed of about 1,600 rpm. Our converter stalls in the neighborhood of 3,500 rpm. All of the modifications combine to lower elapsed time while raising the vehicle's top-end speed."