Each 1 lb. of pressure raises the boiling point by 3 degrees F., so a 4 lb. cap will add 12 degrees to the boiling point- - - -224 degrees at sea level. If the radiator is clean, and you've got an efficient fan, that gives you 44 degrees of leeway between thermostat opening and boil-over with a 180 degree stat. Unless you're operating on an extremely hot day, or working the engine hard, that should be plenty of operating range. The 7-lb. cap would add 21 degrees to the boiling point, but it might be a bit hard on the radiator.
Jerry
Last edited by Hotrod Lincoln; 08/30/2009 8:22 PM.
