Just sharing some recent results of N20 Flash tuning applicable to the 220i and 228i, as well as F20 125i.
Generally we would expect the following baseline figures
220i: ~115kw at the wheels
228i: ~150kw at the wheels
Given the engines are near identical after tuning we expect both to be around mid to high 170s with no other modifications. Downpipe, exhaust and intake can see these crack 200rwkw
Compared to JB4s etc on a 228i they will typically dyno at low 170 rwkw (less torque aswell) and on the 220i you are looking at mid 130 rwkw
If anyone has a 220i I can't recommend a flash tune strongly enough as the gains are in excess of 60kw at the wheels, which frankly makes a 220i + tune a performance bargain
F20 125i Stock: 149rwkw, Tuned: 179rwkw, gain of 30kw & 20%
F30 320i Stock: 114rwkw, Tuned: 174rwkw, gain of 60kw & 52%
For M235i Tuning see this thread