Trans input vs output speed?What equation would you use to do that? Or would it be the mph differential between locked adn unlocked at a given rpm, or rpm diff at a certain mph locked vs unlocked?

 

that would only measure converter slip, not efficiency. basically you need to dyno locked VS. unlocked and that will tell how much power it eats up.

 

If you believe the engine torque PID then you have
engine output HP (torque * RPM * units scaling).

Then you also have the delivered HP as a calculated
PID (with the proper vehicle weight). Now you would
have some added inefficiency in that mix (rear end)
but you could factor that out (if you had a ballpark
value) and be left with the converter & trans element.