Raiator Cap Pressure

[Brent Kasl <kasl100@navix.net>]

According to the Rootes manual, the pressure cap for a 1725 S5 is rated
at 9lbs. I have a 13 lb cap on my sons car and want to correctly replace
it, however, their does not seem to be a 9 lb cap available, and
according to the radiator cap catalog, this car requires a 7lb like my
S2. What is correct and what is everyone running? Thanks Brent