Garrett G25-660 boost control
 

Im interested in results of your turbo. What A/R rear housing you running?
There is so little info about these turbos at the moment so posting some would be amazing, Dyno figures or even what RPM full boost hits in 3rd gear.

What's it doing? Over boosting? Boost spiking? What is your boost target? 1.1 bar is 16psi. if your target boost is 16+ psi then remove the MBC and let the wastegate do it's job.
I've never heard of your boost controller, Is it electric or manual? assuming manual as you said MBC but i googled it and nothing came up. Is it a bleed type or ball and spring?

Sounds like you need to adjust your EBC to a lower duty-cycle to accommodate your faster spinning turbo. Where did you buy your G25-660 from?

Im assuming you've got a set of chips installed for your mods ect right?

First i'd set your duty cycles to the lowest. or turn the controller off and make sure it's not the controller. If it's not the controller, there's an actual issue that needs to be resolved. or just disconnect the vacuum lines from the solenoid.

An EBC needs room to control properly the wastegate in the boost range between the rating of the wastegate spring and the peak boost target. This is the range where the solenoid should show the advantage of an EBC over an MBC, and I have found that this boost range needs to be relatively "wide" on a 951 engine when smoothness and things like throttle-based boost control have to be enabled.

I had nothing but problems running an excessively stiff wastegate spring with an EBC. Running a peak boost of 1.2 bar, I went down from a 1.0 to 0.4 bar wastegate spring which solved my issue. This means I tripled, from 0.2 to 0.6 bar, the width of the effective working boost range of my EBC.

I imagine your peak boost is not much higher than 1.1 bar, and in this case the solenoid used with your EBC may struggle to actuate the wastegate because its spring is too stiff, and it obviously does not have time enough to react within the excessively narrow 0.1 bar boost range to avoid the boost spikes you may be seeing.

I would therefore suggest that you install a softer wastegate spring.

I think I've got this worked out, I can’t believe how much lower the duty cycle had to be set to achieve the same boost pressure, I had to lower the gain down to 10 from 35 as well. Holding rock solid at 18 psi now and the car is running great. I’m hoping to get to a dyno in the next few weeks for some numbers but one thing for sure is this turbo is a huge improvement over the 27/6 it replaced, it's a different car. I plan to log some runs to get more accurate numbers as far as boost vs RPM but from what I’ve seen so far the turbo is all in under 3k and there’s a ton more power everywhere, part of this Im sure has to do with the head and intake work I had done by Joshua at Valley Performance. I think I’ll post a separate install thread for the turbo build as well. Thank you everyone for your input.

That would be all turbo. Headwork wont improve your spool that much. 100-200 rpm if you're lucky. Head work is more towards mid and top end.
You're saying you get 18psi before 3k rpm???

Any chance you can measure your crossover pipe exhaust pressure to add more data?

Is this the turbo you chose?
871389-5010S 0.72 V-Band V-Band No N
https://www.turbobygarrett.com/turbo...series-g25-660

Yes, I bought it from Turbo Kits the first day they were available with inlet and outlet flanges.

Same amount of effort/fab as GT/GTX to install?

Yes. All Garrett turbos are interchangeable provided they're the same rear housing i.e t3 t4 ect.
it will still require a custom down pipe and modded xover.