[gmza]

The N54 is currently offered in a few states of tune:
225kW@5800, 400Nm@1300-5000 (135i, 335i, etc.)
240kW@5800, 430Nm@1500-4500 (740i)
250kW@5800, 450Nm@? with 500Nm overboost function (Z4 sDrive 35is)

INITIALLY the N55 will be offered in only one state of tune:
225kW@5800-6400, 400Nm@1200-5000 (launched in 5GT, now in 135i)

The N55 will, during the course of model year 2011, replace the N54 in *EVERY* application where the N54 is configured for 225kW. This is all the *35i models. The N54 will continue to be used in higher-output applications (e.g. 740i and Z4 sDrive 35is).

I had originally seen a power/torque graph of the N55 suggesting 430NM configuration (on mwerks.com as far as I can recall). This appears to have been misreported and subsequently removed. It must have been the graph for the N54 in 240kW tune.

It is, however, being widely suggested that a higher-tune version of the N55 will ultimately replace the higher-tune versions of the N54, however, this hasn't been announced yet. As with most BMW motors (look the the N52 in *25i and *30i config and N54), higher-output versions typically only follow a few years after the engine has been in the market in a conservative state of tune (long enough to assess reliability).

Below is a comparison of the N54 (in 225kW tune) and N55 (225kW).