BRAIN EXPLOSION!
After a little more thinking i may have just come up with a simple way to get torque directly out. Almost no calculations.
Going on the idea of a water based load cell. Once water is introduced into the turbine cavity it will create restriction and so forth, ok nothing i didn't already know. But if the water pump house is floating, ie on a bearing. I simple force gauge can be mounted on the casing of the pump 'holding' it in place. The force as the pump torques up it trys to turn, Putting force on the force gauge. Simple Force X Length = Torque!
It wont give an accurate reading but it will give a comparable reading.
This could work for a torque converter no?
This is soooo doable. I could even get a data logger and plot the toruqe vs rpm on a screen.
Now that i think about it, any load cell will work with this setup.
Hmm i quick wiki search shows that this is the normal way of measuring torque. zzz