Struggling with controlling boost, seeking help here:
Even so the car is NOT an A3 (2003 A4 1.8T), here is the setup:
Turbo: K04 turbine housing, machined for RS6 turbine wheel.
Compressor: RS4 housing, custom fabbed to fit 2283 billet wheel
550cc Bosch EV14
High flow log manifold
3" DP
S4 MAF
FMIC
SAI, N249, N112, EGR/Kombivalve, removed, tuned out.
Wastegate actuator: stock, starts to move at 4.5 psi
Goal: constant 22 psi (MAP limit) to 7250 redline
Tune: we were running into the 'calculated' EGT cut embedded into the Bosch/Audi ECU. Instead just blindly eliminating the threshold, we decided to measure and log the actual EGT at the manifold. Result: showing about 200 deg C lower actual than the calculated ones.
Consciously raised the EGT threshold so it does not 'cut in'.
The problem:
a) N75 control not smooth at high rpm. Tried a few N75 (factory versions), but no significant change.
b) switched to 'ball and spring' (intergrated engineering) MBC. Now experiencing: when MBC set to 22 psi, boost falls to 18 psi after 4500 rpm. When set to 25 psi (gauge), falls to 21 psi after 4500 rpm. Curves are almost parellel. Why are we 'overboosting' mid range (or NOT holding boost at high rpm)?
Any suggestion how to achieve our goal to hold 22 psi to redline without too much overboosting (stock rods) at mid range?