Saw this SIB posted:
Various aftermarket "N54 - Engine Performance Tuning" kits are being
aggressively advertised to BMW owners.
Depending on the manufacturer, these modifications may consist of a
"turbo-tuner control module" (piggyback box) plugged directly into the TMAP
sensor / DME connector, waste-gates vacuum plumbing alterations, or the DME
"performance" software programming.
In general, each aftermarket tuner claims a significant increase in engine
power and torque of up to 40% over the stock N54 engine specifications
(which are, respectively, 300 hp and 400 Nm).
These alleged performance gains are achieved by an increase of the
turbochargers boost in a wide range of engine speeds, in some cases
exceeding the maximum designed turbo pressure of 8.8 psi by 50%.