Recommendations to go from 300hp to 400hp

[kcasper72]

I know this is a generalized question and there are probably a thousand things I can do to improve the horsepower. I have a 2013 535i xdrive with the msport package. It is completely stock. I would like to take it from the 305hp it has up to at least 400hp. What are your recommendations? Most cost effective add ons is what I am looking for most bang for the buck so to speak.
Thank you all in advance.

[BimmerBreaker]

Jb4

[pbonsalb]

JB4 or Cobb Access Port or similar piggyback tune. The N55 is limited by its small turbo, but you should be able to add at least 20% to your current power, maybe more.

[ezbmr]

I like the Cobb, it will read trouble codes as well. Super easy to do.