Click Personal Profile after login to opt out. I used the exponential to model the output torque of the converter. Basically, you need to decide how much torque is required to move the vehicle and set the paramenters of the exponential so that this torque is produced at around 1000 rpms.
Car manufacturers seem to have varied the lock up setting over the years.
I might be able to help more if you described exactly what you want the model to accomplish. We also have a lockup clutch which independently locks the torque converter out. Having a dig around on the web I can find no open source data that really gives more than that. It is very complex - mapping a torque converter gives a whole bunch of graphs. The name by which you'll be known in the forums.