Boost falling off

[vrracing]

Relevant mods

90 S5 Vert.
JDM Tii
Pineapple Racing street port
BNR Stage1 turbo
Bonez cat-forward. Corksport cat-back with Vibrant UltraQuiet resonator.
RTek Stage2
720/1000cc injectors
Zeitronix w/b
HKS EVC Black Edition

With the EVC off, we were seeing a max of about 4.5psi so I'm assuming the wastegate spring is about 4.5pounds. We set the EVC to 50% and we were expecting about 7psi max (4.5 + (50% * 4.5)) but it went to ten; which was fine.

As you can see in the Zeitronix chart, boost is maxing out at ~10psi at 4700RPM and drops off gently from there.



We are using Aaron Cake's rule of thumb AFR tuning targets

0-4 PSI: 12-12.5
4-8 PSI: high 11s
8 - 15 PSI: mid to low 11s
16 PSI +: high 10s

but obviously the 1000cc secondaries still need to be pulled back some. IIRC we are pulling them back about 3% above 4500RPM.

Is the fact that we're getting too rich after 4500RPM what's causing the boost to fall off or is the wastegate spring at fault?

Thanks, appreciate any guidance yall have.