I am in the process of piecing together the materials to make a mild steel short runner manifold out of weld elbows for my Evo 3 for an Evo X turbo which I am getting from gcmBob. The goal for the car on 93 pump gas is 14psi on 10:1 CR on a 2.2L motor so nothing too crazy. I haven't heard of the Evo X's having any boost creep
I am not sure about cutting the stock flapper off exposing the 2 ports to the separate ports in the turbine housing and doing an external wastegate off the O2 housing as the 2 separate exhaust paths will essentially have a small chamber to share. which in my mind defeats the purpose of going twin scroll. He has advised me that since there is no real flow happening in the "chamber" until the wastegate opens that it should not really make much of a difference. Couple that with the fact that the stock flapper is not air tight against the face of the opening.
I will have to reclock the compressor housing either way to have it exit pointing downward.
Option 1 (cheapest)
Keep the internal wastegate setup and have new mounting points for the actuator welded onto the compressor housing. This keeps the 2 exhaust paths seperate until they meet the turbine blade.
Option 2
Cut the flapper off and mount a Tial 38mm MVS off the O2 housing
Option 3
Weld the flapper shut and take the effort and build a merge collector with a divider wall that is flush with the face of the Tial's valve face.