I have been having difficulty with my current turbo suffering overboost spikes then dropping off dramatically before gradually climbing back towards the target boost. Having cleaned and checked multiple sensors I decided it must be the VNT duty in the map not being compatible with this turbo.
After some head scratching about how best to approach this, as remote remapping of the VNT would take forever sending maps back and forth and really the duty needed to be setup on the road while driving. To achieve this I dragged the MF2 fuel solenoid controller from my water methanol kit out, coupled it with a pneumatic valve from my Apexi boost controller that lay in the garage and slapped together quickly a VNT controller using boost and rpm feeds.
The mapping took about five hours and a quarter of a tank of fuel with two people, one driving, the other adjusting the potentiometer for the 500rpm intervals. The results were excellent, hitting peak earlierand holding at that level right upto the red line. So now I have proved the turbo is spot on and the fueling is not an issue but I need to try to translate the output of the controller into something that could be applied in the map.