what is a torque converter and does it get damaged when you manually rev match down shift?

woah all your info is weird.

first things first. engines are connected to gearboxes via clutches or torque converters. clutches are metal plates that come together and transmit power with friction. a torque converter is a sealed unit that transmits power via fluid viscosity. watch this video to understand how a torque converter works.

I know it's old but it does an amazing job. (a torque converter is the same thing as a fluid coupling)

http://youtu.be/leCEmJA0WsI

now to explain what is weird about what you have told us.

in a manual gearbox, the driver operates the clutch with a foot pedal. the driver also manually selects gears by moving parts of the gearbox to select different ratios. to change gears smoothly, gearboxes are equipped with synchronizers. they force the engine speed to match the gearbox speed as you release the clutch. in heavy downshifting, the shock load on the gearbox and engine can be very high due to the differences in speed from the engine to the gearbox. to minimize this shock load and extend the life of the clutch, gearbox and drivetrain, some drivers will rev match meaning they tap the accelerator while the clutch is disconnecting the engine and gearbox. this brings to engine up to a closer speed to the gearbox so that when the driver lets off the clutch there is less of a speed difference to be handled by the synchronizers.

in an automatic gearbox there is no clutch. it's a fluid coupling/torque converter. this is because for a long time, it was hard to get a computer to manage a clutch well. torque converters allow for a transfer of power with some slip so that the engine doesn't stall. downshifting at high RPMs in an automatic car (even with manual mode) does not damage the torque converter, they are meant to provide a level of slip. along with the synchronizers, this saves the drivetrain from large shock loads.

in recent years, computers have gotten good enough to mange clutches. automated manual gearboxes are those that have a clutch that is controlled by a computer. they have the instantaneous power transfer of a clutch with the convenience and ease of driving of an automatic. These gearboxes are most often seen in high end sports cars. when using manual mode in a car with an automated manual be is single or dual clutch, the engine computer cuts engine power during shifting. some cars with a sport mode have a rev match function to minimize drivetrain shock. in either case, you should not be rev matching.

the only case when you should be rev matching is when you have a car with a manual gearbox. automatics and automated manuals have programming built in to do the job of rev matching and do not allow for "corrective" behavior from the driver during shifts.

if this was all too complex, then this is the way to explain it. if your car has 3 pedals, you can rev match. if it has 2 pedals do not. in fact, even if your car has 3 pedals, you should just try to avoid rev matching. if you get it wrong, you do more damage than good and unless you are driving on a racetrack and actively and extensively using engine braking, you do not need to minimize drivetrain shock loads. drive the car like normal and it will last a long time.

How are you revving the downshift on an automatic?

An automatic does not work like a manual transmission.

Yes you will heat up the fluid if you stick the auto in neutral and rev it.

This will not only damage the torque convertor but do the transmission in as well.

A torque converter is part of am automatic transmission. Sounds like you have a manual tranny, talking about rev matching.

Thats an interesting question and I hope you find some reasonable answers