With my setup (K04 size compressor, K03 turbine, stock fuel, 50hp chip) I boost 18.5 psi at 4000 rpm, drop to 10 psi at 6500 rpm.

I saw a spring set at ECS for the DV valve. Could playing with the various spring settings help me?

 

The boost drop you're seeing is not a problem with your DV, its just characteristic of the K03 turbine housing. That turbo runs out of breath north of 6k RPM. You could fiddle with the DV spring but I doubt it would help much.

 

That's what I think. Next step is to take care of the turbine side (currently still K03 wheel and just a bit optimized housing) by going to a K04 based housing and use a larger turbine wheel (just hope I am not loosing too much spool up and early boost). Compressor (similar to K04 wheel) seems fine for my goals.

Can the ECU/chip 'pull back' on boost if running out of fuel? Or just timing? I was expecting (with 18 psi at 4000) that the fuel will run out.

Still looking for someone who wants to get rid of his "K04" (GIAC PC16 or similar) tune and put his chip into my 2nd ECU I have standing by (so I can the matching injectors; AFPR 3-5 bar also standing by). Anyone?