I'm not a tuning expert, so just speaking from my experience, last fall when I added k and n filters and Viking header, I left the O2 sensor connected and used the same tune. Bike ran well but felt alot of heat on my leg. This spring I disconnected sensor, made sure it was shut off in tune, and reloaded the tune. My leg says it is running cooler. I really think the 02 sensor leans it out at idle, the bike might run rich at higher rpm range. Looks really good by the way, if you go the dynotune way I would wait till all your mods are done.