Thanks spinwing,
My question was prompted by the following observations: with the aircraft on the ground, well ballasted, one throttle at idle and the other fully open, rapidly raise the collective to 35-40% engine torque, and observe how long it takes for the parameters (NR, torque, N1, ITT) to settle down at the new setting. Initially the NR will droop somewhat, then surge higher than before, drop again, etc., before settling down. The #1 engine took about 4 times as long (both in seconds and in number of high-low surges) to stabilize as the #2 engine; however, it does eventually stabilize.
What I was hoping for is a hard number (either seconds or number of surges or “cycles”) before which the engine must stabilize following a power change. At the moment we’re not sure if this is a fault that needs to be rectified, or just not as good as the other engine but acceptable.
I have flown a few B412s whose engines just wouldn’t stop hunting, from +/- 3% N1 at flat pitch to +/- 1% in cruise even in dead calm air, and they all required an AFCU change on one engine to rectify that problem.