I added an H pipe to mine with the O2 sensor in it. The deal is that you want the termination of the H pipe right at 500mm from the valve to the opposite side. Think from the valve, down the pipe, across to the other side. Mine ended up just under the oil filter and still in the front of the skid plate. For this engine you want to shoot for 508mm primary, a 95mm collector and 508 secondary to the muffler. A duel exhaust with H pipe you want the primary to be considered from the valve to the opposite side termination. The secondary length is less critical but is 1.5x longer in a perfect world.