So this might be a stupid question, but what exactly does a torque converter do? What is the benefit of having one?

 

The main purpose is to allow the engine to reach a higher rpm, and thus more HP and TQ from a stop. I can stall my 4000 up to 3500 rpm on STREET TIRES before it starts to break loose. In drag racing, this is really useful, because you don't have to wait for the engine to get into its powerband. Also, the shift extension, or the rpm that your engine drops back down to after a shift, moves up, allowing the engine to stay more in the powerband, and not drop out of it. For example, my shift extension is 5100 rpm, WOT at the strip, once I get outta first, it never drops below that until I let out.

I dropped 6 tenths in the quarter by swapping converters and strapping on drag radials.

 

Simply put, a Torque Converter multiplies the torque from your engine.

A higher stall TC allows the engine to get higher in the RPM band where the car makes more power - hence the torque is higher and the multiplied torque out of the verter is correspondingly higher.

A simple example of how they function would be: If you have an electric fan, set up another fan directly in front of the first but have the second fan face the first. Now turn on the first fan - you will notice that the air coming off the blades of the first fan will hit the static blades of the second fan and make them turn also - even though the second fan is not turned on.

Same thing is happening inside the verter, only the medium being used is tranny fluid instead of air used in the above example. There is the 'driving fan' which is attached to the engine visa-vi the flexplate, and the 'driven fan' which is not physically attached to the driving fan, but floating directly in front of the driving fan and attached to the tranny visi-vi the tranny input shaft.

The engine rotates the 'driving fan' which imparts a shock wave to the fluid and directs it towards the 'driven fan' when the wave hits the 'driven fan' it makes it turn which then turns the internal parts of your tranny. The angle of the blades of both 'fans' has a direct effect on the speed of the 'driven fan' and the torque multiplication that is produced. The 'driven fan' never turns the same speed as the 'driving fan'. For example the 'driving fan' may turn (2) complete revolutions for every (1) revolution imparted to the 'driven fan' by the fluid wave.

The only time the (2) sides of the verter are turning at the exact speed is when the TC Clutch engages - then the input side and output side of the verter are as one and the speed 'IN' = speed 'OUT'. In the olden days of non-lock-up verters there was never a direct mechanical link between input and output as there was no lock-up clutch.

There is a lot of other components included inside a verter and this is a very simplified explanation as to the process (fluid dynamics) that is taking place inside...

-Jay-

 

Thanks for the insight guys.

 

Not a stupid question, how else would you find out if you never asked...

Just like the 1QUIKWS6's fan analogy...

The impeller (driven by engine) shoots fluid into the turbine (drives trans. input shaft) making it spin;
the fluid exiting the turbine's center passes thru the stator (remains stationary during torque multiplication) which deflects the fluid back into the impeller's center in the same direction as the impeller's rotation (assists the impeller), this is what multiplies torque (the fluid's velocity vector changes which produces an acceleration vector, and from F=ma the fluid gains 'force').


The TC...
a. allows the engine to idle,
b. multiplies engine torque so you don't need as many gears,
c. allows the engine rpm to drop less at the end of a shift (so engine is higher into its torque band and can pull harder at the start of the next gear) like DOUBT IT said,
d. on launch, allows engine to rev up into its torque band so it won't bog down on the mass of the vehicle;
e. has a clutch which is locked by the PCM for cruising speed fuel efficiency,
f. heats up the fluid in a hurry (this is not good).