well if you are thinking of swapping a motor in vitz, then i assume that you are serious about power and can spend reasonable amount of cash... having said that i will recommend you 2zz-ge, as its the same generation to the vitz engine.... but as we are in pakistan and i havent seen the zz-ge either in lahore, peshawar or pindi so i think the only option remains 4age blacktop....
but try to find the zz-ge, even if it is expensive, the power gain is also quiet big over the bt..
as for nos i thik storm has said it right, i wont risk more than 60shot (safely) for the zz-ge and i think 30 is the max for the vitz.....