seems like alot of work just for a header i hope my obx doesnt need as much work im hoping to just bolt it in and go lol

the problem is that they seem to look the same

3" Exhaust
 

At what point does the exhaust expand to 3" for what everyone is calling a 3" exhaust. Does this type of exhaust connect to the stock headers? Does it expand from the cat convert back?

yes the 3 inch is a cat back system the header replaces the cat though for a full catless exhaust but its a 2 inch pipe then joins into your ehxaust whether it be stock or oversized

So I got it to settle down now after disconnecting the sensor and it took alittle bit but smoothed out. I'm think that the sensor is too far back in the pipe and not getting hot enough.

sounds reasonable though it should be self heating and it doesnt go off of heat it actually reads a/f ratio did they put the sensor up off of the exhaust? like did they use an anti fouler or anything to compensate for the cat alot of muffler shops will do this thinking its necessary because their used to doing newer cars

its just a normal o2 senor, but what do you mean by anti fouler?

alot of people use a sparkplug anti fouler (found at autozone or advanced auto in the help section) it raises the o2 up out of the exhaust and limits the flow to basically simulate a working cat

In the old cast iron manifold the sensor is pretty well in the flow with it being between the two banks of 3 about 6in from the exhaust ports. Now what i'm trying to do is figure out if I can weld the downpipe to the header and still be able to get it out of the car.I'd like to wrap it further down and knock down some of the noise coming from it. It sounds like a v8 with open headers under the hood now. And I plan on moving the o2 location up the pipe much farther. It does make a nice inprovement in power though, not sure how much but noticable.