is it worth it? i think it's best to quote rave669 here:
"wrong, wrong, wrong... I love you guys (seriously, I do) but you entirely miss the point of a torque convertor.
It doesn't raise your idle RPM's at all, that's what the IAC valve (Idle air control) is for.
A torque convertor is the equivalent to the clutch pedal in an auto tranny.
The torque convertor spins freely, until it reaches a certain RPM, at which time it will lock up, thus engaging a given gear.
If your stall speed is 2K rpms, it's as if you let out the clutch at 2k RPM's, so, if you want to rev higher prior to the torque convertor locking up, you change the stall speed to, say, 3K rpms. it's like holding in the clutch longer prior to launch, and is a much needed upgrade for the automatics out there.
The valve body decides the time between gears, a valve body calibration kit is the equivalent to a short shifter in a manual.
Unlike a manual, each gear has it's own clutch ring, trans fluid flows trhough the galleyes, ball valves and solenoids in the valve body under pressure, as the pressure in the valve body rises with revs, the gears are engaged in sequence
With a sportshift tranny, the driver can manually select gears. However, raising stall speed and recalibrating the valve body will make it much more responsive.
Autos shift at a certain rate to find a comprimise between comfort and pulling power from the factory, leaving much room for improvement. also, less time between gears and a slightly higer stall speed will actually prolong the life of a auto trans (just like avoiding granny shifts/riding the clutch does in a manual) because it prevents excessive wear.
Also, since many trannies are computer controlled these days, they can be electronically recalibrated through Performance modules, but is not nearly as effective as an actual physical upgrade.
I can see lots of good resons to put in an aftermarket torque convertor.
BTW, the cooler your tranny fluid is, the firmer and more responsive the automatics will be, a tranny cooler is a great upgrade for starters."
hope this helps some