The radiator I have is a stock(on the outside) 56 but I have it rebuilt with an additional row of tubes to help with the cooling. The radiator guy said to use a 4 pound pressure cap but since I am using a 351w engine my mechanic pals tell me that 4 lbs is not enough for this engine and that I need 12 lbs to keep the water in the radiator. The problem is that all the caps I can find which are the correct dimensions don't go over 4 lbs. I am sure someone has solved this problem before. Thanks for your help.

 

Hmmm, I'm not much help regarding a stock radiator, but I have an aluminum Griffin rad with a 14lb. cap on my 351.

 

Are you going to run an overflow tank? Are you running any other accessories, like AC? If not the 4lbs on should be fine, I run one on my 49 with a 350... I was told at one time that the Bronco or Dodge cap should work...

 

My radiator is a stock dimension 4 core from Mid-Fifty. I use the recommended 7 lb cap also from them. I have no cooling problems with my 460 w/AC in CA.

 

You need a better mechanic. Using a pressure cap on an old radiator is a good way to split seams, or other related damage. They weren't designed to be under 14lbs of stress. I had a 4lb cap on the stock 6 cyl. radiator I used with a 289, and I had no issues whatsoever. I don't know why anyone would tell you the SBF would blow the water out of the rad without higher pressure in the cooling system. That makes no sense at all.

 

7lb cap on a 302 here

 

OLD OLD OLD 4lb cap...mild 289 and I have had no issues. It spits once in a while if I get to rev happy...but my cap is probably close to 15 years old.