Flathead water pumps ??

I'm running the stock water pumps on my 59AB, and am having a Mustang radiator modified to suit. I need to know how much pressure I can subject them to before they'll start leaking? I believe a stock 1947 system is 4 lbs? If so, maybe I can get away with a 7 lbs cap? The Mustang radiator came with a 13 lbs cap, but I think I'm gonna have trouble if I use that

 

I run a 7 lb cap on my flatheat and it came with 4 lb.I wouldnt go any higher though.Thats with a new raditor.

 

Sorry about spelling. Flathead Not flatheat

 

Thanks F1James. That verified my thoughts.

 

you need to stay at 7lbs or less, 4lbs

 

7 lb has worked for me