My first thought was that BMW is simply telling the truth about the minimal power gains, where aftermarket companies simply lie about the "gains" they get.
Originally Posted by Needsdecaf
FYI, almost all turbo exhausts are minimal power gains, unless accompanied by a tune. Just saying.
2013 BMW 535i ED-11/23/12 Redelivery- 1/12/13
1978 BMW 320i (paused project)
2009 BMW Z4sdrive35i (ret.)
1995 BMW M3 (ret.)
1987 BMW 325i (ret.)