Rad Cap PSI

A buddy is putting in an overflow tank on his 70 Challenger 440 and was wondering what PSI rad cap to run? Would it be any different than original?
Thanks in advance

15 lb cap for coolant recovery systems. Remember that the overflow tube must go all the way to the bottom of the recovery tank so that the coolant can be 'pulled back' into the engine upon engine cooling and that the overflow tank must be vented.

must use a vented rad cap with the recovery system also(small vent valve on bottom of rad cap)

a non vented rad cap will not let it recover coolant when cooling down...it will let expanding coolant out though



15-16 lbs on the rad cap psi