Hey to all, I have a 63 544 with a b-20 fairly stock engine. The cooling system consist of a Howe racing cross flow radiator large enough to support well over 300 hp. I currently have the radiator cap plumbed into the top radiator hose and I`m thinking of running a 13 pound cap. If I run a lower psi cap there may be a problem with the coolant flow lifting the seal and thus loosing coolant into the catch tank at high RPM. I would like to keep the catch tank set up that has been installed already. The question is how much pressure will the heater core stand, giving it is in good shape? And what is the original pressure cap rating for the 63 544. I know the heater core design for the 140 Volvos are of the same design and the radiator cap is (I believe) 13 psi rated. Any help would be appreciated. Thanks Larry