I have a V6 heaterblock on a mk8 style heatbreak and extruder assembly. This arrangement is working but I'm having a bit of a problem with underextrusion when printing too quickly. I start encountering problems with 0.2mm resolution, 0.4mm nozzle and around 50-60 mm/s print speeds with 1.75mm PLA. I have even had to raise temperatures by about 20 degrees celcius to try to counter this but I still have some underextrusion. Using 0.1mm resolution and the same settings is fine however. I find when I push filament through the hotend manually, the first little bit comes out easily but then starts providing more resistance and I can't push filament through as quickly; particularly compared with the standard mk8 heaterblock. I have checked my firmware settings for the thermistor which I havn't actually changed as it is the same as the Mk8 thermistor I believe. The mk8 heatbreak in question is 40mm long and has an external m6 thread and an internal PTFE tube lining along the entirety of its length. The PTFE lining goes all the way up to the nozzle inside the heaterblock. It seems to me that the PTFE tube is insulating the top part of the heaterblock and drastically reducing the meltzone and steady heat transfer in the hotend, hence leading to the underextrusion hysterisis I'm experiencing. The short side of the all-metal V6 heatbreak sits in the hotend so I would expect that to act as part of the meltzone and just wanted to confirm that is the intended design of the V6 hotend assembly? I really should and want to put the whole V6 assembly on my printer and there are already designs available on thingiverse I could use (for the Anet A6). I believe E3D are working on a new, even lighter extruder than the Titan Aero however so I will wait until that is released.