I just noticed that despite the larger crank pulley on my AE92 Levin GT-Z the air bypass valve mod hadn't been done to it. So I did it, with zero effect. Note that I was going by seat of the pants as I don't have a boost gauge. I theorize that:

A: The black smoke coming out of the tailpipe (indicating a filthy rich mixture) that is still present means that it's running too rich to feel any change
B: It has been disabled internally
C: It's seized shut and has been since I got the car.

So until I get a boost gauge I can't be sure about what is happening. But still... I just checked the fault codes and there is none present (as was suspected). The only other thing I have left to do is to check the ignition timing. If it's set too advanced it *could* be on the edge of pinging on lower boost and retarding a lot on high boost thanks to a knock sensor, diminishing any power increase.

Any thoughts or other issues?

Yes checking the ignition timing probably should have been done earlier but with the wrong pulley on it (and only a single timing mark on the new pulley and indicator) I wouldn't know what mark represents anyway until I pull a spark plug.

*edit: Also, I reverted back to the stock plumbing, just in case...*