BMW's N54 engine has won the International Engine of the Year award for the past two straight years. It has also been listed as one of Ward's 10 Best Engines during the same period. The engine produces 306 hp and 295 ft-lbs of torque in a 3.0L inline six package thanks to the use of twin Mitsubishi turbochargers and direct injection. The N54's quick response and smooth torque curve has been an attraction for many enthusiasts, including myself - I call my Montego Blue coupe the turbo Cookie Monster. That is why a few BMW 335i owners are miffed by a feeling of reduced performance after a recent service update. Posters on the BMW forum e90post.com claim that a software update to adjust rattling wastegate valves has induced lag into the turbochargers that wasn't there before.
As illustrated in the gallery below, the N54 turbochargers differ from most setups in that the wastegates default to the open position. This allows for better emissions due to the ability of the exhaust gas to bypass the turbochargers on start up so the catalytic converters can heat up faster. It certainly follows suit that BMW has the ability to adjust the ECU settings in order to hold those wastegates open, thus altering the turbochargers' peak boost point and adding to the perception of lag. Currently all performance degradation discussion has been based on seat of the pants feel, along with increased exhaust noise and fuel consumption. Despite the claims, BMW North America and service centers have, thus far, found no critical issue with the new settings. If owners want to present true evidence, they should use a simple OBD scanner device to data log the manifold pressure or simply run a dyno comparison test. Thanks for the tip everyone!