I am starting the process of converting a 1Z motor's vnt-15 to a VNT-20.
Yes, that is correct. The current system is this:
RC2 with mods for VNT control, among others.
A4 MAF, new n75 valve
2 1/2" exhaust exiting in front of the rr wheel. No restrictions.
Free flowing intake, Audi FMIC...