Clutch Fan disengage speed

[joesauer]

Does anyone know the approximate RPM that a 68 radiator clutch fan disengages.  I'm converting my 68 350 no air to a Vintage Air setup & will be installing the ac radiator & shroud.  Considering a 7 blade clutch fan instead of an electric.  Thanks.

[JohnZ]

Although a viscous fan clutch never completely disengages, they're calibrated to go to their minimum engagement level over 3500 rpm.