great answer but I'm not sure it's the answer to this question....J. Kidd said:they share a resonator and muffler.
All 6 cylinders dump into two header banks - 3 cylinders per. The 3 tubes squeeze down into one and continue the length of the car (times 2 - one for each header bank). These pipes share what seems to be some sort of resonator and then finally they share the muffler. This is a very efficient exhaust. A performance mod available for other cars with dual exhaust is an "x-pipe" where, on a V8, each cylinder bank goes down the pipe, meets at an "x" and then splits again. The theory is the x does not restrict exhaust flow but actually balances out exhaust pulses aiding in performance. Sharing the resonator the way our cars do seems to me like it would accomplish the same thing. Also having the dual pipes share the same muffler saves in the weight of an additional muffler and still flows very well (as long as there are just as many outlets as their are inlets - which our mufflers have).
Hope that answers your question.