Torque Converter
We're replacing the OEM torque converter because once the power gets to the transmission, the torque converter gets the brunt of the engine's raw torque. From there, the torque converter has to act as a buffer between the engine and the rest of the transmission, transferring the power smoothly and efficiently. However, when faced with the challenge of transitioning power from a modified engine, the stock converter isn't up to the task. The OEM converters are made along the fine line between quality and performance and cost efficiency of mass production.
Notice a few of the differences between the stock converter and the BD converter we're replacing it with:
The front of a stock converter is an economical piece that is stamped steel with threaded lugs welded to it where the converter bolts thread into it. (fig. 12 & 13) Under heavy stress caused by high performance or heavy towing, the front plate can warp or even crack. Notice the hot spots on the friction surface of this converter. (fig. 14) They are in the six spots where the metal lugs are welded to the plate. The rest of the surface has "ballooned" outward, so it doesn't fully contact the clutch material inside the converter. Also notice that the OEM converter uses only one clutch along the outside edge of the plate. These characteristics severely limit the amount of power the converter will hold before it begins to slip and heat the fluid up enough to boil in no time at all.
BD's converter uses a stamp forged steel front cover that is much thicker and more rigid than stock. There is probably 60 percent more steel used here than on the stock front cover. This eliminates warping and flexing, which gives the clutches a smooth, even surface to grip against. (fig. 15) Yes, clutches. BD's converter uses two large clutches to engage against the front cover instead of one. The outer clutch engages first and the inner clutch engages second for a positive, no-slip connection.
Let's also compare the OEM stator wheel to the BD stator wheel (fig. 16):
BD CNC cuts its stator from billet aluminum for a precise finish. The OEM stator is cast aluminum for mass production. BD changed the pitch of the fins on its stator to allow more efficient engagement with the passing fluid. This provides a lower stall speed and, in turn, earlier transmission engagement. This is great because it allows you to take advantage of the large amount of torque that comes early in the power curve on the Cummins motor. The lower stall speed makes the transmission more responsive and increases fuel economy because it puts more power to the ground.