Update: Please have a look at the MK2 version: https://www.thingiverse.com/thing:2552668

A fan duct for K8400 printer head from Vellemann.
It helped me a lot to print nicer overhangs and an absolutely nice 3DBenchy compared to the high-velocity or nor duct at all.

Added "fanV3_duct_k8400.stl" with additional PEEK blowout for two nozzles.
Added "fanV3_duct_k8400_rightonly.stl" for version with right nozzle only.
Already has additional outputs to blow against the PEEK cooler.
Additional blowout needed for metallfill-filaments

It is designed to be immediately be clipped onto the original fan.
You may have to bend the metal piece a bit which holds the fan.
Hope this helps some people to print nicer and more efficient with their K8400 while not changing too much on the original machine.

I've been using other fan ducts for my K8400 before but this one is the most efficient for me.

I absolutely(!) recommend to apply some stripes of Kapton tape onto the heater block.
It makes the heating more efficient and the temperature measurment and control much more stable! Only one or two layers needed - no need to make a huge bulb arlound the nozzle!
I think this is because of the gap and position of the temperature sensor. In the original setup it will be cooled a bit by the fan. But this effect is minimized when winding some Kapton stripes around it - See images.

Can be printed without supports - see print settings below.