Downpipes (Overboost?)
 

This is going to be a long thread so bear with me.

I have a 2015 BMW 120i F20 LCI with the N13 engine. (Turbo is Garrett MGT1549 ZDL)

It already has a K&N Drop in Filter, 70mm Cat-back exhaust, GFB DV+, Wagner Competition Intercooler, Racechip Ultimate, and NGK 5992 plugs from the Mini JCW, I run it on 99 Ron fuel.

I am planning on replacing the downpipe with a catless version, has anyone faced with boost spike or boost creep after fitting a catless downpipe on a piggyback tune such as Racechip? Unfortunately remapping the car is out of the question for me at the moment.

I posted here as the N13 engine is very similar to the N18.

Have you tried a BMW forum?

I thought the boost control improved when I replaced the down pipe with a cat-less version. With less back pressure, seems easier for the waste gate to control the boost pressure.

Won't running a catless downpipe give you a dashboard error without a proper remap?

yes

You should have no issues with boost spike going catless. It's common on Subaru's but BMW's control method is different. The racechip is the wildcard. Normally with the stock tune you lose a little bottom end but pick it up on top. With a proper tune its power across the board.

No. Information on the N13/N18 is far more extensive here.

Yes it will, thats why I am planning to cancel any error codes from the downstream 02 sensor.

Thanks!

Does anybody know if the downstream narrowband O2 sensor effect AFR and fuel trims on the N18 engine?

It does not. It's sole reason for existing is to monitor the cat efficiency.