• If you increase the area of the "Turbine Exhaust Gas Inlet" (nozzle) while the area of the "Turbine Exhaust Gas Outlet"  stays the same-- more power will be available to overcome compressor loads that are trying to slow the turbine.  This is what I understand Continental did to allow us to use a lower rpm in cruise.
  
In any case we are dependent upon rpm of the rotor to provide the compressed air at the pressure and volume we need. 

It's easy to see that if we reduce the volume of air entering the Turbine Exhaust Gas Inlet, the less torque will be available to turn the compressor.  At some point the compressor load will cause a stall.  I guess it's debatable whether or not it's compressor or turbine. Results are the same.  Compressor quits. As I understand it, and the fix was to give the turbocharger more exhaust air volume at lower engine rpm.