I'm on the way of fabricating custom manifold for twinscroll T3 setup and need some suggestions about what diameter runners to go with

have an option of next diameter tubes:

38mm internal diameter
38.6mm (42mm outer diameter)
44mm (48mm outer diameter)

car is 2.3, setup would be just regular low mount turbo (HX35)
looking forward to fabricate 4" turboback as well

 

 

44 and I would do a T4 twin scroll

 

turbo already has T3 flanged hotside, so I'm staying with it...

can you elaborate little more, why T4 or why 44mm ?