the time is getting closer to finishing my single turbo setup and as no one makes an off the shelf downpipe im getting a friend to fab one up.
my question is do i need the o2 sensor i have an apexi pfc and have heard you dont need one but in the pics ive seen of kits some how an 02 sensor nut

 

You don't have to run an o2 with the powerfc as you can disable the option. But if you don't have an o2 bung, how are you going to tune the car :P.

thewird

 

Put a bung in (or two) regardless of whether you intend to run a sensor at all times or not. As pointed out you'll need one for tuning. EGT bungs aren't a bad idea to tack on too.