I wanted to write up some info to this, as I've just swapped the factory EL manifold for a UEL setup. I couldn't find much detailed info on this subject, so if I can shed some light, then my mission will be complete.
Background Info:
Subaru used the "Y" shaped equal length manifold on NA engines from 1998 or 1999-2005, with the pipe bolting up after it containing the catalytic converter(s). From 2006 onward up until 2010 (I think), They changed this manifold to a different routed equal length, that contained a catalytic converter built in, and both o2 sensors on their respective sides. The proceeding pipe contains another CC. My 2007 X had a factory exhaust, nothing was ever touched aside from rusty flange repairs. I recently got the infamous P0420 code, naturally. I suspected the cat(s) had failed, as I diagnosed the o2's and found them to be functioning properly. I knew I was going to have to replace the manifold as the cat was built in as previously stated. Furthermore, for some time I had been debating an UEL setup for the rumble, so this would be the two birds and one stone deal.
The Headers:
As far as I am aware, there are no aftermarket headers for this 06+ factory setup if you want UEL. What I mean is that there are no UEL headers that are completely plug and play with the rest of the factory exhaust system.
My Setup:
This has previously been done, so I decided to go the same route. I purchased some 99-05 Impreza RS UEL headers, which are readily available on eBay and other retailers. As I stated earlier, the collector flange will not fit up to the factory cat pipe. The flange on the UEL headers is actually several inches away and facing in a different direction. The solution is running a pre '06 cat pipe. If you run one of these cat pipes, it should be a direct bolt on as mine was. You could go custom fabrication for either the headers, the cat pipe, or both. You could cut the 3-bolt flange off the factory cat pipe, and fab a new pipe up to run to the header flange. However, I will explain why I didn't go this route in the next section.
The o2 Sensors:
If you do a custom fabrication, you can choose the placement of you sensors, obviously. If you are thinking about doing the swap the way I did it, then the o2 sensors must be relocated. The factory manifold has the o2's in front and behind the built in cat as previously stated. This part of the manifold is located by cylinder 1, adjacent to the valve cover on that side, underneath. The harness for the sensors runs along the top of the cylinder head, underneath the injector bracket, towards the front of the engine. The harness connectors are secured to a bracket, and bolted into the block with a 12mm bolt. The pre '06 cat pipe that I purchased has three bungs; one on each side of the front cat, and one at the back of the rear cat. I chose to relocated the sensors in the two bungs on the front cat. This would be a similar setup to the factory's, only further back towards the subframe. Hence the need to move the harness for the o2's. This in my opinion is the easy part of the job, and it was the first thing I did. I disconnected the battery, first thing. Then I removed airbox, and intake hose for more room to work. After that, I unplugged both o2's from their connectors. Then I removed the four 12mm bolts holding the injector bracket. You might have to remove the breather hose off of the valve cover, but I can't remember for sure. After moving the coil plug wires out of the way, the bracket should come right off. Then I removed the bracket bolt that secures the sensor harness connectors. I'm sure you can remove the harness connectors from this bracket, but mine would not come off, so it was quicker to zip the bolt off. Finally, you should then be able to reroute the harness towards the back of the engine. I was able to reach the harness connectors back by firewall and secure them near there. From there, I went ahead and installed the new headers, and installed my sensors in the new cat pipe. The bung at the rear cat was plugged and not used. With the harness relocated, as well as the sensors relocated further back. I was able to reach the connections with the new locations. I didn't have to extend any wires.
The Rest Of The Exhaust:
If you run this setup, the exhaust after the pre '06 catpipe is really up to you. If I had to assume, an 03-05 fozzy catback should fit. The factory 06-08 resonator pipe would probably work too. I'm not entirely sure about it because all my flanges were cut off and pipe welded together before I purchased the car.
Some Things To Consider:
If you buy a cheap eBay set of headers, the build quality between each unit is probably not consistent. Make sure when you fit the headers on that everything clears, and is not making contact with anything, like the oil filter or subframe, etc. Some adjustments might need to be made in order to make them fit.
Make sure that the o2 sensor wires do not make contact with the cv axle, as they are near that general vicinity. My upstream sensor's wire is about 4-5 inches away from the cv boot, but is fastened securely, and does not move much.
If for any reason you need wires extended to reach. I would splice in more wire at the engine harness, and not the o2's harness itself. I've heard of people extending o2 wire, but I wouldn't recommend it. They are sensitive sensors and it's an expensive mistake if you compromise the unit. They make harness extenders that plug into the sensor, but I don't have any experience with those. Ideally, it's a better day if you don't have to do any of this, and the sensors reach just by relocating the main harness.
And lasty, by swapping from EL to UEL, the car will probably make less power, as this setup is less efficient. My car is already super slow, so I personally don't care. You may also experience a CEL if you do this, because you are changing the overall function of the exhaust system. I'm not sure if that is a definite, but I wanted to at least disclaim that just in case. My P0420 has not returned and I've been running this setup for almost 2 weeks, with a few hundred miles driven since then.
I hope this thread is helpful, and if you have any questions, suggestions or corrections, I will update it.
I can link parts and add photos of what I'm talking about if needed.
Cheers!
Background Info:
Subaru used the "Y" shaped equal length manifold on NA engines from 1998 or 1999-2005, with the pipe bolting up after it containing the catalytic converter(s). From 2006 onward up until 2010 (I think), They changed this manifold to a different routed equal length, that contained a catalytic converter built in, and both o2 sensors on their respective sides. The proceeding pipe contains another CC. My 2007 X had a factory exhaust, nothing was ever touched aside from rusty flange repairs. I recently got the infamous P0420 code, naturally. I suspected the cat(s) had failed, as I diagnosed the o2's and found them to be functioning properly. I knew I was going to have to replace the manifold as the cat was built in as previously stated. Furthermore, for some time I had been debating an UEL setup for the rumble, so this would be the two birds and one stone deal.
The Headers:
As far as I am aware, there are no aftermarket headers for this 06+ factory setup if you want UEL. What I mean is that there are no UEL headers that are completely plug and play with the rest of the factory exhaust system.
My Setup:
This has previously been done, so I decided to go the same route. I purchased some 99-05 Impreza RS UEL headers, which are readily available on eBay and other retailers. As I stated earlier, the collector flange will not fit up to the factory cat pipe. The flange on the UEL headers is actually several inches away and facing in a different direction. The solution is running a pre '06 cat pipe. If you run one of these cat pipes, it should be a direct bolt on as mine was. You could go custom fabrication for either the headers, the cat pipe, or both. You could cut the 3-bolt flange off the factory cat pipe, and fab a new pipe up to run to the header flange. However, I will explain why I didn't go this route in the next section.
The o2 Sensors:
If you do a custom fabrication, you can choose the placement of you sensors, obviously. If you are thinking about doing the swap the way I did it, then the o2 sensors must be relocated. The factory manifold has the o2's in front and behind the built in cat as previously stated. This part of the manifold is located by cylinder 1, adjacent to the valve cover on that side, underneath. The harness for the sensors runs along the top of the cylinder head, underneath the injector bracket, towards the front of the engine. The harness connectors are secured to a bracket, and bolted into the block with a 12mm bolt. The pre '06 cat pipe that I purchased has three bungs; one on each side of the front cat, and one at the back of the rear cat. I chose to relocated the sensors in the two bungs on the front cat. This would be a similar setup to the factory's, only further back towards the subframe. Hence the need to move the harness for the o2's. This in my opinion is the easy part of the job, and it was the first thing I did. I disconnected the battery, first thing. Then I removed airbox, and intake hose for more room to work. After that, I unplugged both o2's from their connectors. Then I removed the four 12mm bolts holding the injector bracket. You might have to remove the breather hose off of the valve cover, but I can't remember for sure. After moving the coil plug wires out of the way, the bracket should come right off. Then I removed the bracket bolt that secures the sensor harness connectors. I'm sure you can remove the harness connectors from this bracket, but mine would not come off, so it was quicker to zip the bolt off. Finally, you should then be able to reroute the harness towards the back of the engine. I was able to reach the harness connectors back by firewall and secure them near there. From there, I went ahead and installed the new headers, and installed my sensors in the new cat pipe. The bung at the rear cat was plugged and not used. With the harness relocated, as well as the sensors relocated further back. I was able to reach the connections with the new locations. I didn't have to extend any wires.
The Rest Of The Exhaust:
If you run this setup, the exhaust after the pre '06 catpipe is really up to you. If I had to assume, an 03-05 fozzy catback should fit. The factory 06-08 resonator pipe would probably work too. I'm not entirely sure about it because all my flanges were cut off and pipe welded together before I purchased the car.
Some Things To Consider:
If you buy a cheap eBay set of headers, the build quality between each unit is probably not consistent. Make sure when you fit the headers on that everything clears, and is not making contact with anything, like the oil filter or subframe, etc. Some adjustments might need to be made in order to make them fit.
Make sure that the o2 sensor wires do not make contact with the cv axle, as they are near that general vicinity. My upstream sensor's wire is about 4-5 inches away from the cv boot, but is fastened securely, and does not move much.
If for any reason you need wires extended to reach. I would splice in more wire at the engine harness, and not the o2's harness itself. I've heard of people extending o2 wire, but I wouldn't recommend it. They are sensitive sensors and it's an expensive mistake if you compromise the unit. They make harness extenders that plug into the sensor, but I don't have any experience with those. Ideally, it's a better day if you don't have to do any of this, and the sensors reach just by relocating the main harness.
And lasty, by swapping from EL to UEL, the car will probably make less power, as this setup is less efficient. My car is already super slow, so I personally don't care. You may also experience a CEL if you do this, because you are changing the overall function of the exhaust system. I'm not sure if that is a definite, but I wanted to at least disclaim that just in case. My P0420 has not returned and I've been running this setup for almost 2 weeks, with a few hundred miles driven since then.
I hope this thread is helpful, and if you have any questions, suggestions or corrections, I will update it.
I can link parts and add photos of what I'm talking about if needed.
Cheers!
