How can i tell a bbc deep grove pulley?
Are truck pulleys deep groves?

Truck pullies are not deep groove. A deep groove pulley totally caputres the belt in the groove (it does not sit at the top of the pulley flush with the rib, but down below the rib). When used with an outside mass Dayco belt they will stay on at 10,000 RPM (assuming proper alignment).

Larger Dave

Ok thanks Dave do i need to put one on the alternator to?