Difference in the catalytic converters - Rear O2 position

[Huffer]

Ok, so my 98 GT SEDAN has a dual cat system where the rear O2 sensor is WAY back by the end of the cat - in the pic below you can see that the front O2 sensor is up by the header - pre cat.

The rear O2 sensor is actually positioned much further back, behind the 2nd cat. I thought this was normal.

In comparison, my 98 GT WAGON has a dual cat system except that the front O2 sensor is in the same place near the header - pre cat - but the rear O2 sensor is a mere 15" away, sitting right behind the 1st cat. See this pic:
https://sl-i.net/FORUM/images/imported/2008/06/SubaruCatalyticConverterCARBstanda-2.jpg
(O2 sensors are to the right = front of car)

On the SEDAN, the cat section is all one piece, like this:
(just imagine a smaller diameter pipe, with a short, stubby cat)
https://sl-i.net/FORUM/images/imported/2008/06/7022xxImpreza1-2.jpg

See where the O2 sensors are?
In the first pic, the O2 sensors are very close.
In the second pic, the O2 sensors are a long way apart.

[Huffer]

And now I know why - my GT wagon is manufactured to CARB standards, whereas my GT sedan is manufactured only to Federal standards.

Hopefully this information will be useful to someone, somewhere...

[2.5GT]

good info.

and would the new cat trigger a CEL on CARB certified subarus?

[Huffer]

Well here's the weird thing - on my SEDAN, the one with the rear O2 placed way back, I needed a new cat, so I purchased one that looks like the Random Tech model. After I installed it, I triggered a PO420 CEL. Main Cat Inefficiency.

So I go to install the rear O2 spacer and discover that because of the position of the O2 bung, I cannot do it without moving the bung to the side of the pipe, because the default position is on top of the pipe, too close to the body of the car.

So my federally certed car (sedan) is triggering a PO420 with a federally certed cat, whereas my CARB certed car (wagon) isn't compatible with any of the Random Tech style cats anyway...

However - the wagon can lose the 2nd cat pipe without causing any sensor issues, as the 2nd cat (see first pic) is AFTER the Rear O2 sensor.

[sybir]

If you want a real laugh, my OBX headers have the rear cat mounted in the non-CARB location, so I had to run a 49-state jumper harness to be able to mount the rear O2.

That's not the funny part.
The funny part is that I don't have any CEL's (after 4 months) with equal-length headers and a cat-delete......my exhaust is straight through all the way to the muffler. :D

Go figure; the only codes my car ever threw when I had Borlas and a high-flow cat were for rear O2 sensor heater malfunction every couple years......replace the sensor and fix the problem.

*shrug*

[Huffer]

More pics:

Federal:
http://www.thepartsbin.com/images/products/images/eastern/40237.jpg

CARB:
NO PIC I COULD FIND

Federal REAR Cat:
http://www.thepartsbin.com/images/products/images/eastern/40497.jpg

Federal Front Cat:
http://www.thepartsbin.com/images/products/images/eastern/40273.jpg

RandomTech Dual High-Flow:
http://www.ultrarev.com/files/images/product_thumbnail/t_41990.jpg