This is the thing that baffles me so much with the N54. This kind of turbo pressure just screams inefficiency and short term reliability. Unfortunately I've had some issues getting to completed with the port/polish head for the Z4 so my TD04 twins and related upgrade parts are all on a shelf until that is cleared up. But my hope is to be at 600whp on emix and be just under 20psi. Possible? Not sure. But tons of boost just tells me the engine is not set up to make the power. And the N54 as designed, is not made to make this power reliably, IMHO.
Maybe more so with a big single, for sure. Seems much tougher with twins. Glad it is working for you, but I don't see 27+psi in my future - I think it is working the wrong end of the problem
Filippo