Hi, find below a description on the APR as (optionally) installed on the C650.
The automatic performance reserve system is used only on takeoff and operates regardless of the engine speed synchronizer switch position (FAN/OFF/TURB).
The automatic performance reserve system works in conjunction with both electronic engine controllers and the engine speed synchronizer.
Relays in the automatic performance reserve controller are controlled by engine speed detectors within the controller which sense N 2 between the two engines. When N 2 exceeds 5 percent and the automatic performance reserve system is activated, automatic performance reserve thrust is produced. Increasing thrust approximately 200 lbs on the operating engine.
The electronic engine controllers of airplanes incorporating the automatic performance reserve system are adjusted to allow a one percent in N 2 and a 45°F (25°C) increase in ITT operating limits. Under normal conditions (non activated automatic performance reserve system) the controller transmits trimmed signals to the electronic engine controllers which regulate the engines to normal limits. When automatic performance reserve thrust is required, the relays within the automatic performance reserve controller are de-energized. When de-energized, the N 2 and ITT trim signals are removed and the limits are increased to automatic performance reserve levels.
Hope this helps.