I have a dual-extruder N2, and have little interest in using the second extruder (I wish I had bought a single-extruder).
This is an improved right-side fan duct for much better part cooling when only the left extruder is to be used.
It directs All of the air from the right-side OEM 35mm fan onto the part, instead of wasting 3/4 of the airflow on cooling an unused heater. By moving one connector on the printhead, you can also program the fan speed in your slicer for perfect cooling.
Note that it requires removal of the right nozzle and that clearances are tight. I moved the washers from outside the fan, to the left, inside the duct, to clear the cooling fins.
I printed it in PolyPC polycarbonate in .1mm layers, with glass/gluestick bed at 110 and extruder at 264.
I hacked this from the Raise3D stls, using Tinkercad.
While I was at it, I scaled a matching left-side fan-duct to the same height as the final injection-molded piece used by Raise3D - about 3mm taller than the Kickstarter version.
Both ducts are included here.