Sort of -- it's a matter of having air or exhaust mass appropriately matching the volume of relevant chambers (including within the engine) it will flow through for optimal intake, combustion, and exhaust.
Too big a diameter for the mass means the speed will slow down, too little and it will backup (i.e., "back pressure"). This will vary enormously with RPM and even more so when boost is involved (valve overlap and timing come into play here too, BTW).
With a turbo, usually the "bigger piping the better" rule holds primarily because the turbo itself restricts exhaust flow, but just going bigger isn't necessarily the solution. Something that just smooths out flow (i.e., minimizes existing restrictions) without massive changes in tubing diameter will probably make a world of difference alone, which is suggested by those dynos.
Also, if they keep VVEL on this motor, it should play a
much greater role in tuning FI than it has for NA. The rate at which AF mixture is drawn in, combusted and then expelled to turn the turbine of the turbo will be critical to optimal power and responsiveness, and there will be more wiggle room to play with potentially.
The most flexible way to do that would be tuning the mechanics of the valve timing and overlap, as a purely mechanical change will be fixed and require some compromise to achieve best output across the rev range.
Judging from that dyno, Nissan did a good job making the twin turbos offer high performance practically right off idle.
Now if you with a bigger set of turbos in the mix (or a gigantic single turbo), then yes, you may need bigger piping.
OEM, my guess is that one turbo is dedicated to bottom end torque and the other to top end, and they balanced the transition so well, the torque curve is reminiscent of a roots blower's output.
Anyway, I want
