On a N/A EJ25? I'm talking about from header back. That would eliminate a need for equal-length headers (though it would probably cost about the same) and flow about as much exhaust as a single 2.25" pipe.
I'm sure you could get some older Honda cats to work in there. Mufflers would probably be the toughest part. Or bring them together just before a single muffler. The EG velocity probably ain't that great by then anyway.

 

I doubt anyone has tried it. no reason to.

 

It would be pretty cool just for the neatness factor, but there's no real performance gains to be expected from it.

 

I expected as much. I'm new to the boxer engine and Subarus in general, but not to cars altogether, so I have to ask odd questions.

 

The problem is the 02 sensors.

 

Are there (3) O2 sensors on these cars? If not...please explain why it would be a problem. Or better yet, where are the O2 sensors located?

 

There are 2, they are located in sequence, and designed to read flow pressure and maybe temp as well... Thats why aftermarket exhaust systems cause CEL's on them most of the time. If you were to split the exhaust in two, you will dramatically change flow and temp. Probably the only way to get around this would be to force the sensors to read like they are reading correctly all the time, but the car wouldnt run too well... It is a fun idea though.

 

Exactly, a huge can of worms...