What to do with O2 sensor w/aftermarket exhaust?

FWIW

Well the 02 sensor reads the exhaust and adjusts everything accordingly to what it reads. Now if the 02 sensor is not reading correctly it will adjust and give improper signaling and the system will not run correct. I would have a hole drilled into the pipe and weld a nut to allow the 02 sensor to be put back into the system.

If somehow someone figured out how to lock a specific map into the ecm ????? Don't know how it would be done with the 02 sensor still hooked up??? then it would be fine. however if the system is running a closed loop than it requires the sensor to give the correct fueling. More than likely it will run rich as the sensor is reading super clean as no fuel burn. If for some reason it decides to run lean, you could burn a hole through the piston like a cutting torch.

So funny how people muck with stuff they don't understand??? I see so many people run custom exhaust on cars and remove the 02 sensors thinking they will get more performance??? They are put there for a reason.

It wont run to max performance or spec without it.

I also have fmf header and just removed o2 sensor from the bike (had it custom mapped on dyno later).

I did a bit of Air Fuel Ratio (AFR) testing on my 2009 570 in stock form with lambda probe disconnected, and I found the actual fuel map to be quite good, so in my opinion theres no downside disconnecting it, no error code will be thrown either. AFR was right around 13:1 in any position, tad rich on wot but not below 12:1, i.e wont affect power imo.

Id disconnect the lambda and plug or seal the connector.