Fuji's explanation is the best...
...and consider this.
Back in the day when I was on the stock VF39, my tune was set at 20.5 psi at
peak (I can't remember right now what RPM that was but somewhere around 3800?)
and then it tapered off.
However, after reading Fuji's post, it makes me wonder if this was why I eventually
cracked the hot side of that turbo on the wastegate housing.
Food for thought :tup: