Well, it sounds like you're kinda interested in this so... You will not run too rich without a downstream o2 delete. There are 2 o2 sensors, one (and this is the one you need and the one you'll run rich without) is in the exhaust manifold RIGHT BEFORE the flanges that connect the rear exhaust manifold and the downpipe together. The 2nd o2 sensor is in your ubend ( which of course you already knew) You DO NOT need the 2nd one. The PCM you got from Mike is tuned so you wont throw any codes without it. Trust me, I dont even have mine plugged in (you can see where it plugs into a wire harness. Just follow the o2 sensor about 6 inches under the car and you'll see where you can unplug it) Do you have emmision tests where you live?? If not, you can get this whole custom DP made for really cheap. The whole setup (cat, ubend, res delete) can be a VERY simple/cheap process. All the guy needs to do is, make a cut one inch in front of the cat and one inch behind the resonator, and weld in a straight pipe in its place, this is of course if you do not have emmision tests in your area. But whoever you're talking to about this, has the whole o2 sensor/running rich thing a little confused because there are 2 sensors.

If you want me to, I will make up a drawing for you real quick of what/where the cuts and welds need to be and this whole explaination I just gave you will be alot easier to understand. I know when I explain things, I tend to babble and be VERY repetetive. But if you dont have emmision tests, this whole DP and res delete should be very cheap and easy.
You know what, Im gonna go ahead and do the half-baked drawing for you so you see what im saying.

 

I had a local muffler shop perform the u bend delete and resonator removal for like...$50. No, I did not notice any performance gains...we're talking maybe 2 or 3 horsepower and NOBODY can tell that by the seat of their pants.

Regardless, this is just something that makes me feel good...about my MC!

 

Wait, you didnt notice ANY gains?? I noticed a huge... well not HUGE, but I sure as hell felt it.

 

what if i dont want to do the res delete? i still want a res and cat...

and how restrictive is the stock downpipe?

 

Well if you wanna keep those two, it still wont throw any codes or anyhting. And there will still be some restriction in teh cat and res but you'll get most of the restrictions out of the way by getting rid of the ubend.

 

but how restrictive is the stock downpipe? i guess, will i really have a difference between getting rid of the stock downpipe and just the ubend?

 

Its not a BIG difference but I would notice a differemce betweem the two.