The big advantage is that two cylinders from each side of the engine go into a collector, as opposed to all four cylinders on one side of an engine. This in effect lets the exhaust from one cylinder pull the air out of the next cylinder during the exhaust stroke. The flow rate increases and is smoother than standard headers. Another advantage is that it frees up some room around the sides of the engine(for over the top models), and keeps some heat away from the starter. A small disadvantage is that they can get the distributor hot. Make sure to use a heat deflector, and insulate well.