I have a 1974 F250 4x4 with a 1967 390. I also have the huge 4 row HD radiator.
I want to replace the radiator cap, the old one says 17-19 pressure.
Which is the correct pressure one to get. I have NO AC.
Thank you!

 

You can easily look up the pressure spec for that truck, I'm not going to for you. What I will say is that cap pressure is relative. More pressure equals more wear on the pump seals, more chance of blowing a radiator hose, etc. More pressure also equals less risk of boiling out if it does get hot, and less use of coolant if it doesn't have an overflow tank. A lot also depends on the temperature of the thermostat, a 165 degree thermostat can generally get away without even having a pressure cap.

13psi is a nice safe medium for many older vehicles, I'd go with that in general not knowing any specifics about your rig. That said on one of my rigs I've damaged the pressure seal so it holds no pressure, and on others have run as much as 20, it all depends.

 

13 psi.... In run a catch can too.