I believe this is stated in the POH.
Based on standard Piper Seneca V (PA-34-220T) training procedures derived from the Pilot's Operating Handbook (POH) and standardized operating procedures, the zero-thrust setting used to simulate a feathered propeller during single-engine training is:
Manifold Pressure (MP): 11 inches (11” MP)
Propeller RPM: 2000 RPM
