Let's say you have a converter with a 4000 RPM stall speed. When you mash the gas from a stop, the motor will flash up to 4000 RPM before you launch. Now let's say that when you shift, according to all the formulas and whatnot, you should be at say 3600 RPM. Now since your foot is on the floor, will the converter flash up to 4000 RPM? Or will it stay at 3600 and accelerate like a converter of a lower stall speed? If anyone is confused by this please let me know. Thanks in advance.

 

OK here's the (or "an") explaination.

The torque converter sits between the engine and transmission.

It allows engine speed to be different from transmission speed.

A 4000 RPM converter allows the engine to turn 4000 RPM (or some reasonable approximation thereof) and the transmission to turn 0 RPM. Of course there is tremendous torque all over the place at this point but technically if you welded the drive shaft to the body you could keep this up indefinitely, or at least until something overheated or broke.

Shift points are controlled by the governor, valve body etc, which are all in the transmission (on a NON-computer controlled transmission).

So as far as the governor is concerned, we are at 0 RPM. So no need to shift.

I believe what would happen in your scenario is that you would mash the pedal, the engine would jump to 4000 RPM. You would start to move, and accelerate until transmission speed was 3600 RPM. At this point the transmission would shift into second, dropping tranny speed down to (say) 2000 RPM. You would keep accelerating until tranny speed was 3600 RPM again, and shift into third. This would keep happening until you ran out of gears or got pulled over.

I believe during this whole time the engine speed would never drop below 4000 RPM. It might rise slightly as transmission speed rises, but I don't think it would rise much, since the torque converter would just be un-multiplying as the transmission speed rose closer to the engine speed.

This is similar to what I see in my RS. I've got a 700-R4 with a 2500 RPM converter, and if I accelerate moderately (enough to get it to stall up to 2000-2200 or so, but gently enough that it shifts early) I see an almost constant engine RPM. It only goes up slightly (50-100 RPM maybe) as I accelerate (which wierds out my stick-driving friend, he calls it "constant-RPM accleration").

On a completely computer-controlled transmission I do not know what the effects would be, since the engine RPM is so different from the tranny RPM. It is possible of course that those types of transmission have a separate "tranny tach" so the computer knows how fast the tranny is turning independently of the engine.

 

That's essentially correct.

Think of it this way: the torque converter has no way of looking rearwards at the trans and asking it what gear it's in, and even if it did, it has no mechanism for adjusting its behavior accordingly. All it knows is the difference between engine speed and stator speed (which is 0 RPM), and to a far lesser extent, input shaft speed. The stator properties have a far greater effect on stall speed than the input shaft does. So, for all practical purposes, the converter will act the same in all gears and at all vehicle speeds, and its action will depend solely on engine speed, with only minor effects originating from any other conditions.