To make sure my response was clear to 2engsout. It does not wait for an rpm difference. The engines are sync'ed. If one goes below a set RPM then it idles the other one.

How slow does a big gasser idle? I have never tached one? I will do that at the field today if I can remember on my 50cc gas aerobat. I can program the the rpm it decides an engine has failed and right now I assume a failed engine at <2 rev/sec (120 RPM). Maybe I should raise that if a prop is free wheeling due to airspeed?