No, actually we Canadians do happen to know bronze from brass. The advantage of using brass for valve cages is that the brass will deform slightly under pressure from a steel valve during the combustion cycle, and this very slight deforming increases the ability to give a 100% airtight seal between the valve and the valve seat. There is nothing wrong with using bronze, except that being a "harder" metal the bronze will take a longer time to give the same sealing effect. I have built over 20 i.c. engines, all with brass valve cages, and they all perform quite well.