Cobb AccessPort on our 335i project car. As with other AccessPort installs, it couldn't be easier. We plugged the AccessPort up to the car's OBD-II port (it's by the driver's left ankle), and selected "Install." Fifteen or so minutes later, it was all done. We pulled the car back on to the dyno and observed a substantial gain in power, and even more in torque. We picked up 49 hp at the wheels, and a whopping 72 ft-lbs of torque.
Note that the graph here shows uncorrected numbers, and my previous graph was using SAE correction. I posted the uncorrected number here because although the ambient temperatures were the same, the relative humidity levels were different by 4%, and I think the SAE correction was too heavily weighting the humidity difference. But corrected or not, the gains are pretty impressive, especially considering how easy the install is.
Speaking of torque, the additional grunt really points up the 335i's lack of a mechanical limited-slip rear differential. While the "electronic differential" does work, the car has a hard time coping with so much torque, and the feeling as the power gets shuffled back and forth (as the car grabs first one rear brake caliper and then the other) is unnatural and disconcerting. We're looking into fitting our car with a mechanical limited-slip differential.