Basically...all the nitrous is doing is freezing a set amount of air...well once that air shoots into the manifold it does NOT distribute evenly therefore most of the frozen air will cram into cylinder one then two then three then four because it will choose the path of least resistance when trying to squeeze into the cylinders...with direct port the nitrous is freezing air in the runners which gives equal amounts of nitrous to all cylinders which in turn allows all cylinders to have pretty close to the same pressure in them so that cylinder one isn't working overtime to help cylinder four keep up. When that happens in a single fogger system you put more wear on cylinder one because it is trying to do double work. That is about the simplist terms I can put it in.