[Shane@DBPerformance]

Bolt-ons can make a huge difference in the tune also. The car is tuned from the factory to run with a stock exhaust at stock boost levels. The more airflow the ECU sees, the more it overcompensates with the fueling. Some people can run fast without any tuning device because the MAF screws up and overruns and doesn't actually get a correct reading of the airflow and the car doesn't go insanely rich, or they don't have enough fuel pump or injector, which can help lean it out. Or if the MAF messes up too much, you go too lean and knock. What did the datalogger say for knock? Have you checked for boost leaks? They are main cause of mysteriously low power.