I dont understand how torque converters multiply torque....????

 

Try this link. It explains basic torque converter operation quite well.

http://www.howstuffworks.com/torque-converter1.htm

A little addition to the above:

When there is a large rpm difference between the pump and the turbine, like when you brake torque or first launch, the oil coming off the turbine and being redirected by the stator hits the BACK side of the pump (which is attached to the engine) and gives it a push. That's what multiplies torque. It may appear to be lifting oneself up by your own bootstraps, but it does work....as long as there is a large rpm differential.

The torque multiplication factor can be 2.5 times at stall in some converters, but as soon as the turbine (and the driveshaft) start to move, the multiplication drops off very rapidly.

 

I think they use calculators hehe.

A very simple example:

Think of a torque converter as two gears that instead of a chain coupling them together, pressurized fluid is. Now replace the gears with turbines.

Since the fluid pressure (and hence force transferred) varies based on the rotational speed differences of the two, it may take a little speed at the driving side turbine (engine side) before it can illicit motion on the driven side(transmission/gearing side). Once motion occurs, the driving side may spin or move twice as much fluid per rotation as the other side so it willhave twice the force (hence multiplication)


This is for your 'minds eye' so no wise cracks from the peanut gallery about the inaccuracies