I am attempting to understand this modern marvel the automatic tranny. In another thread, we started talking about how they can get better performance with a shift kit and a high-stall torque converter. But I'm still a little fuzzy on some details - I'm hoping someone who knows a whole lot will be willing to talk about it.

I get the design, and that there is a torque multiplication while the engine is turning faster than the drive shaft (when they are at 1:1, that is "stall"). The reason it's good to have high stall is that you get more time in the multiplied-torque stage - thus, a steeper torque curve and faster take-off.

Also, the shift kit will make shifts happen faster, even though they may be less "smooth". The engine will spend more time driving wheels than transmission fluid, and this improves performance in obvious ways.

When does the transmission shift gears? Is this related to stall speed?

In the POS I drive to work, I decided to floor it and see what happened. From a stop, I hit the accelerator and screeched the tires off the line and the tranny stayed in 1st until redline! Then it shifted up and the tires screeched again. In no time (wish I'da measured it) I was at 65 MPH and had to back off. Funny though, if I just ease off the line, it shifts at 2800 RPM, sometimes lower. On the highway, it's about 3400 RPM from 4th to OD.

Does that mean that my POS tranny is a 6500 rated stall? That would seem a little unlikely...

What is the TH400's specs as far as comparing with aftermarket custom torque converters? Does the TH400 use pressure-sensitive shift valves or servos? (I know it must be valves in 69.) Can you modify shift points? Again I suppose it relates to stall speeds?

Wikipedia has nothing useful - I looked.

Thanks!
Chris

 

Neither do I.....but its Friday!!!