The proper term for the valves is probably "pressure release valve." In the NA, oil goes from pump through filter to block. The relief valves in the block release pressure and bypass the filter if it clogs. In the TT, oil goes from pump through filter tree to the oil cooler and then to block. The TT oil filter tree has relief valves. If you just put the TT tree on the NA block, you potentially loose oil pressure to the block because of the back pressure through the TT cooler and hoses.
