If you want the turbo sell the car and get a 335
Not a lot you can do to a 328 that is cost effective
power wise.
http://www.e90post.com/forums/forumdisplay.php?f=378
http://www.e90post.com/forums/forumdisplay.php?f=16
water pump , serpentine belt tensioner, vcg and ofg gasket
leaks are the common problems.
biggest noticeable difference in the lci is hood creases.
get rid of the Run Flat Tires.