If the only thing that was done was to add another exhaust pipe flange, that manifold is junk. The correct way to split an exhaust is to add a divider that almost, but not quite separates the runners into two segments, and add the extra flange to the rear section of the manifold behind the heat riser area. Leave about a 1/4" slot above the divider to allow a little circulation between the two halves while the heat riser is in the "closed" position. The idea is to split the exhaust into sequential pulses that alternate from one pipe to the other. Done right, it creates a very distinctive exhaust note, and just might create a tiny power advantage. It's mostly eye candy to impress at a show and shine.
Jerry
