Converter Basics
Scott Simpson
What is it?
The torque converter is the piece that connects the output of the engine to the input shaft of the transmission. It is a round gadget that looks like an oversized donut and bolts to the flexplate (also referred to as the flywheel.) The stock Turbo Regal has a 12" diameter converter stamped D5 D5 D5 all the way around the face of the converter. It is a unique special high stall converter from the factory. The factory stall speed is approximately 2200 RPM.

Note: many transmission shops may be unaware of this special converter and could possibly swap yours for a standard 12" torque converter that stalls at about 1800. How can you tell? With such a low stall torque converter, the 250+ HP V6 won't be able to break the tires loose on the street. (Something to watch out for when buying a TR )

How Does it Work?
Through the use of fins on the inside of the torque converter and transmission fluid getting pumped into the converter at fairly high pressures, the input and output speeds of a torque converter can be vastly different, or the same.

A 12" or 9" converter refers to the diameter of the unit itself. In general, a smaller converter will have a higher stall speed. To oversimplify, stall speed refers to how high you can rev the engine before the torque converter will no longer "freewheel" and attempt to turn the tires. But since the tires don't want to turn over because of friction, the motor begins to stall. A lockup converter will have a clutch disc inside of it (much like a manual transmission) which, when the torque converter is "flooded" with tranny fluid, will lock up (same as taking your foot of the manual trans clutch pedal.) To flood the torque converter, fluid needs to get into the converter at a much higher rate. To do so, a Torque Converter Clutch (TCC) solenoid inside the valve body of the trans opens a plunger which creates an additional fluid path that "floods" the torque converter with additional tranny fluid...locking up the clutch mechanism inside the torque converter.

The TCC solenoid is activated by the ECM based on 3 engine inputs, VSS, TPS and gear indication. A sticking solenoid will cause the transmission to bog down the engine during deceleration. To replace it, one needs to simply remove the trans pan and remove the two bolts that hold it in place and disconnect the wires to the 3rd and 4th gear indicators. A new solenoid comes with new wires.

Which One Should I Use?
Converters come in several "flavors" ...
  1. Lock up stock style converters. These are usually 12" converters that have a lock up clutch in them. Modified versions can have a stall speed of 2600-2800 rpm, depending on the construction. The lockup clutch is engaged under light throttle situations (cruise), which allows for greater efficiency, less heat generation and slightly better mpg. When racing, you can lock the clutch under WOT with a switch or with a race chip. This practice will gain about a tenth in the 1/4, but will eventually wear out the clutch.

  2. Non-lockup converters. Available in various diameters. The most popular version of these is a 9" converter that stalls in the 3000-3200 range. There is no lockup clutch, so at cruise there is some slippage (200-300 rpm usually). They work very well on big cam/turbo combos. You trade off some heat generation (from the slippage) and efficiency losses, for the responsiveness gained. You need to make more HP to gain enough advantage in staying in the "sweet spot" of the RPM/torque/HP band to overcome the slippage losses and reduced efficiency.

  3. 9" and 9.5" lockup converters. These are hybrids that try to combine the best of both worlds. They allow for the higher stall and responsiveness. However, due to the smaller size, there isn't as much clutch surface available, so if they are locked up under WOT you can burn up clutches fairly quickly. Newer 9.5" converters are built with more clutch area to counteract this, while still allowing 3200-3500 brake stall.

    The non-lockup style converters have more "slippage" by design. A properly operating clutch converter will have less slippage (even unlocked, due to its lower stall speed). Going to a higher stall converter is usually necessitated by the owner also installing a bigger turbo and/or camshaft. Therefore, before you buy a new converter, discuss your combination with the potential vendor to decide which converter is best for you.

Last updated: