Hi everybody. I have a few problems going on my car right now, but I wanted to keep this thread just focused on one. The only thing in the way of e85 and 400whp+.. No matter what I set my WGDC at, the car either boosts to spring pressure (1bar spring) or 25psi+

Car and mods:
2004 WRX with a Hybrid engine (04 WRX 2.0l heads with 06 STI 2.5l shortblock) Engine has 31k miles on it. Heads and block were refreshed upon rebuild.

APS SR/40 turbo
Aquamist meth injection @50/50 meth/water mix
Spearco TMIC
Grimmspeed EBCS
Tial 38mm EWG (V-band) 1bar spring
Walbro 255lph fuel pump
Injector Dynamics 1000cc injectors
Samco BOV 100% atmospheric
Perrin turbo inlet
TGV Delete
Grimmspeed PnP exhaust manifold+ Hi-flow crossover
Full 3" exhaust
AEM 3.5bar MAP sensor
AEM IAT sensor (Tapped into bottom of TMIC)
Grimmspeed AOS
2008 STI 6 speed with VSS pro for the speedometer reading from ABS sensor.
Speed Density protune with Cobb Accessport V2

To be clear, the car DOES NOT have MAF sensor installed because i'm running speed density.

The problem: I've been trying to eliminate the wastegate flutter known to be associated with electronic boost control, and especially pronounced with an external wastegate.
I know this is achievable if I run very low wastegate duty cycles. 10-12% should have me around 25psi. That's why i've been using Cobb's recommended setup, utilizing the top and bottom ports of the wastegate. My tuner, Corbin Johnson from Johnson Tuning, also instructed me to route my vacuum lines this way.
This effectively keeps the top of the wastegate shut longer, and my spring pressure comes out to be 20psi instead of 14.7psi (1bar).
I've found out through playing with the wastegate duty cycle that the flutter isn't really heard until higher than 15% or so.

But anyways, i'd like to keep using this vacuum setup but it's not working for some reason. No matter what I put the WGDC at, the car either boosts to spring pressure, or boosts to around 25psi. And it's random. I can do one WOT and it will be spring pressure. Then I can immediately do another pull and it might boost to 25psi. Sometimes i'll get like 5-6 pulls in a row where it boosts to the same pressure, but it's uncontrollable. 20% or 1% it's all the same. The only thing I can do for sure is put the WGDC to 0% and it always boosts to spring pressure then.

So ok, maybe the setup is just flawed. But no, I have an RSTi with the same turbo, same EBCS, same vacuum routing, and a Tial 44mm wastegate. It's boosts extremely smooth and accurately, with no flutter at all. I suppose the only difference between the setups is that the RSTi has a 44mm gate, and it's the old style. I have the new style MVR 38mm gate. But I don't think it should make a difference? And no, I didn't mistakenly use a water port for vacuum. All vacuum lines seem to be good with no leaks. Nothing looks like it's being kinked.

Now here's the catch. If I use any setup where the top port of the wastegate is is vented to atmosphere, the car has no problems boosting and everything is normal. However, I get that damned annoying wastegate flutter because my WGDC is over 15% to achieve high boost. There should be no reason why I can't set the car up like the RSTi!

Also, I just routed my vacuum lines like this (Below) today and the boost worked great, except for it still has the flutter. I have to put the WGDC at 22% to get 24psi vs. 10% (On the RSTi) with the other setup (Cobb).. All I did was flip ports 1 and 2 around, and BAM it works. But with flutter. What the hell is going on? Why can't I run this the other way?

Does anybody have an idea as to why I can't control boost with this setup? Does anybody else run this setup? I've tried calling Cobb on this but got nowhere... Any help is appreciated!

~ Randy