I've searched for this and haven't gotten any answers. Question 1- If you get the obx headers cut n weld on the stock cats are there going to be any gains or is it pointless.
question 2- if u put in the obx headers w/ the 2 deleted cats n o2 sims or whatever so no CEL comes on will you pass smog with a obdII scanner they use here in WA state.
I have 2.25 piping from the 3rd cat all the way back to maganaflow mufflers

 

I honestly think you would see minimal to no gains if you weld stock cats. More importantly, whats the point of buying an aftermarket header to do that?

As long as you don't throw any codes and every thing is cherry with your ECU, you will pass the obdii scan test. It is not hard at all to pass with aftermarket header. I'm not familiar with WA state emission testing laws but I'm sure it is the same as here in AZ.

You could install the header and keep your stock y-pipe. That way you don't completely get rid of all your stock cats. If you want lower end TQ, keep your stock y. If you want more top end HP, swap out your stock y for the aftermarket y.

 

Ok. Will I throw a CEL with the stock Y? I read it somewhere that someone left their stock Y on and didn't throw a CEL

 

Apparently no CEL is thrown if the stock y is removed but I guess its a toss up. Just get a dual output o2 sim and you should be good. Occasionally I get a CEL with my o2 sim but its always the code, I forget now which it is, for the secondary cats. I just ignore and it goes away. I doubt you will have that problem if you buy a new, good quality sim.

 

Ok thanks. So I will need an O2 Sim for post cat and reuse my O2 sensors for precat (just to fill in the holes). That is it right nothing else?

 

The 2 pre-cat sensors must stay installed and stay hooked up properly, they are what controls your fuel. The 2 post-cat sensors are only there to tell the ecu that the cats are working, but do not effect performance. You can use a dual output sim wired to those two post-cat connectors and put 18mm x 1.5 bolts/caps in the holes, and remove those sensors altogether. Or instead of the sim you can install defoulers between the pipe and the sensor which moves the still hooked up post-cat sensors out of the exhaust path and keeps the cel off.

And to the original question, it would seem to be quite a waste to hack up a pair of headers to add the cats back, more trouble than it is worth IMO.

 

if you want to keep your cats you can always swap them for some high flow performance cats