The collector is actually part of the header. It is the part that all the primaries meet. Placement of the sensor on the collector is ideal. If you have to mount it to the y pipe then try to place the sensor as close to the collector part of the header as possible.

A side benefit for mounting them close to the OEM location is you may not have to buy O2 extensions.

I believe you use a 3/4" drill bit. The bung usually just sits on the outside of the metal. Sinking it in the hole may cause issues depending if you use MIG, TIG, Stick and the material you are working with.

Mount the sensor where it will have clearance around it and it won't hit something (ideally 10:00 and 2:00 is what the instructions said) if heaven forbid the car gets bottomed out on a speed bump.

 

Wide-band O2 sensors are carefully heated to, and maintained at a precise operating temperature, to match the calibration of the wide-band controller. They can be placed anywhere because of this.

Narrow band sensors do not start to operate until the reach ~600*F. If they drop below that temp, they don't work. The 4-wire sensors include a heater, but there is not temperature controlled. The further away from the engine, they cooler they run. And, narrow band sensors are very temperature sensitive, particularly when they depart form stoichiometric A/F ratios.

It make perfect sense to put the narrow band sensors as close to the engine as possible.

 

Think your extensions are even long enough if they are in the Ypipe? Something to consider.

 

alright ill just connect them on the collectors. ill try the 3\4 drill and ill weld them in. i may or may not need the extensions. i believe if i put them prolly in the middle of the collector. heres the pictures of the headers on summit. illl place the o2 bungs where they have them placed on these headers

 

http://www.summitracing.com/parts/HO...1HKR/?rtype=10