LOL at that guy "cant think why they did this" with regards to the wall. The reason they did it was to create a basic 4-2-1 effect within the standard manifold; check any good quality downpipe and it will have a matching divider. Cheap pattern parts dont have it, so are essentially a giant log manifold with one downpipe.
Just shows, you shouldnt take anything on the net at face value, especially dicking about with your engine when the person giving the advice isnt sure what theyre doing.
Excellent, open up all the ports, the bigger the better right?