u/xSked

Planning to change downpipe to a 300 cell one and the alibaba exhaust. Do I need to tune car or I can just leave it stock ecu, still got 1/2years warranty left.
Was thinking if ever get some weird issues just pop the stock parts back on and send it in for warranty repairs.

Looking to change my downpipe on my G21 M340i, concern is 200cell will be more smelly ( its my daily car) . Is 300 or 400 gonna be better ? Downside would be the noise reduction as it filters more