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 TurboXS Turbo Back Exhaust

    Click an image to enlarge.
I talk about exhaust systems on my Accord Cat Back Exhaust DIY so I won't talk much about theory here. The main difference with a turbo-back system (as opposed to the cat-back on the Accord) is that it includes everything after the turbo charger: a downpipe that comes from the turbo, a high-flow catalytic converter to replace the stock cat as well as the mid-pipe and muffler that make up the cat-back (see below for a diagram).

Also be warned that any people have reported boost creep and fuel cut issues with upgraded downpipes. See this NASIOC thread for information before deciding that this is the right choice for you!

This diagram details all the major parts of the intake and exhaust system on a WRX and should help you make sense of my explanation above. The image is by Mattr762.

Please read the entire DIY before proceeding. Take particular note of the steps that tell you to soak bolts with WD-40 as you should do that the day before as well as just before you tackle those steps.


Here are the 4 main components of the exhaust system.

Top row: Mid Pipe (MP) and Down Pipe (DP) along with a bag of hardware and a short ram intake
Bottom row: Titanium Tip Muffler and High Flow Cat Pipe

You're going to need a wide variety of tools for this:
Ramps and/or Jack and Jack Stands (you should jack up the front and back so you have enough space to work)
Wood for jack up your car
WD-40 or other pentrating lubrication (Liquid Wrench and PB blaster are others I've heard of)
10, 12, 14mm open end or ratcheting wrenches (nice but expensive, though you can often combine coupons with sales at Sears)
10, 12, 14mm sockets
Socket wrench, preferably with a pivoting head, a long and short would be nice
Socket extensions (at least a 12", other sizes may be handy too)
Breaker bar for those stubborn bolts
Adjustable crescent wrench (or 22mm wrench) for O2 sensor
Anti-seize for reinstalling O2 sensor
Flat head screwdriver(s)
Philips screwdriver(s)
Shop light
Torque wrench
Eye protection when working under the car (lots of rust and dirt and grime will fall on you)

Optional tools that I also found handy:
Strong Tin Snips if you want to trim and re-install the turbo heat shield
Dremel with cut-off wheel and sanding stone. I used this to cut a bracket and also to do some extra cutting and smoothing on the turbo heat shield
Pocket knife to cut zip ties
Extra jack to hold up exhaust parts while removing/hanging them (since I was working alone)
Vise-Grip to hold a nut that I stripped
Impact wrench, for those stubborn bolts
Random 2x4 to break a hard to reach bolt free
Drill gun with steel brush attchment to clean up some of the rusted bolt threads

Jack up your car. I used ramps in the front and then jacked up the rear using the rear differential (with a wooden block to prevent any damage from the jack).

Do this the day before as you want the exhaust system to be completely cool before you work on it. Take this opportunity to remove your under shield and soak all the bolts mentioned below with WD-40.


A little known feature on Subarus is the ability to open the hood a full 90 degrees so that it doesn't get in your way as much. The hood support is designed to be removed and repositioned to do this.

First note the small white grommit on the front passenger strut tower. Pull this out.

You'll also want to disconnect the windshield sprayers as you don't want to bend or break any of the connections.

While holding the hood up, wriggle the hood support out from it's mounting point at the bottom.

Put this into the hole you you opened on the strut tower and prop up your hood.

Here is what the end of the hood support looks like so you know what you need to pull out and what angles you might need to.

Note: since I jacked up the car and backed into the garage, the hood would not clear the garage door so I had to abandon this. You should check your clearances as well.

Next you'll want to remove the turbo heat shield which is buried behind the engine and under the intercooler.

If you remove the intercooler, this task will be easier but I didn't want to bother. With a little finesse you can do all of this without removing the intercooler.

Here is a picture of the heat shield with arrows indicating where the seven 10 mm bolts are. You can't see them all in this picture but I wanted to point you in the right direction. Soak these in WD-40 before you start.

The first two are under the intercooler but if you have a ratcheting wrench, you can get to them by touch.

In the picture you can see both bolts, but they're quite out of focus.


The next set of three are barely visible, but they are quite reachable with the right ratcheting wrench or socket wrench.   

The last two are buried under some cables and you will probably need socket wrenches with short extensions for these.

If you plan to reinstall the heat shield afterwards, keep the bolts and pick the ones in best shape to re-install. I needed four.

Getting the heat shield out is difficult with the intercooler and my strut bar in the way, but I did manage to get it out. Just think of it as a frustrating game of 3D tetris.   

With the heat shield removed you can now see the down-pipe. There are five 14mm bolts holding it to the turbo, only three of which are visible (one has already been removed in this picture). Also note that the 2 top bolts are holding a bracket that is used to mount the heat shield. Soak all of these with WD-40 before you start.

The three that you can see in the picture can be removed fairly easily with the right ratcheting wrenches and or sockets. The bottom most bolt in this picture can be seen from the right angle and can also be removed fairly easily

Note that the two top bolts are actually a removable nut and bolt pair while the others are nuts fastened to studs that cannot be removed.

The trickiest nut is the one that is hidden on the other side of the DP underneath the intercooler (top most arrow in above picture). I tried to reach this from under the car and that wasn't any better.

The best option seemed to be using a ratcheting wrench which fit perfectly, but I just couldn't get enough leverage to break the nut loose. Finally I tried using a 2x4 to exert force on the wrench. Then I hammered the 2x4 with my breaker bar and that broke the nut loose. After that I could do the rest by hand.

Now the DP is free from the turbo, but pretty much stuck in place due to all the other exhaust parts it's connected too.

Those were all the tough to reach nuts and bolts that were accessible from the engine bay. The next phase is working under the car to take off the stock exhaust. I chose to work from the back to the front, removing easier pieces first.

After 5 Chicago winters, my stock exhaust was pretty much fused into a solid piece of rust so removal was quite a pain for me.


First, I removed the muffler and mid-pipe as a single unit. The muffler is held by three rubber exhaust hangers. Here you can see two of them. I only disconncted the rear most one here, by spraying the exhaust hanger with WD-40 and then wriggling the support out of the hole.   

Then I removed the one on the other side of the muffler.   

The mid-pipe is held by one more exhaust hanger and is connected to the cat-pipe by two spring loaded 14mm bolts and 12mm nuts (IIRC). These spring loaded bolts were the next thing I removed.

The threads on the bolts were badly corroded so I used a steel brush attachment on my drill to clean up the threads as best as I could. After that I could break the nuts loose.

There should be new bolts with the exhaust, but keep the stock springs for re-use. I also used some 2x4s to hold up the disconnected end while I loosened the rest.

I decided to switch to a jack to hold up the pipe as it's more stable and maneuverable.

Here you can also see the rubber exhaust hanger that supports the mid pipe. Again, spray the rubber hanger with WD-40 and then you should be able to twist the pipe and wiggle it out of the hanger. A screw driver came in handy for this one to provide extra leverage.

Finally, I disconected the last hanger on the muffler, and laid the muffler on the ground, then lowered the jack and dragged the whole piece out from under the car. Then I separated the muffler for re-use on my Forester XT.

Next is removal of the cat pipe which is held up by a J-bracket and a 14mm bolt (left side of picture). The J-bracket has a curved bottom (hence the J) so even if you remove the bolt, the bracket is held in place and the pipe won't fall on you. The bolt was on there pretty tight so I sprayed it with lots of WD-40. I couldn't get my breaker bar in a good position but I got my impact wrench to fit with the right extension. It took a good 10-15 seconds of hammering away with the impact wrench before it came loose. Keep this bolt for later use.

Also in this picture you can see the wire harness for the O2 sensor, which needs to be disconnected next.

Here is another view of the O2 sensor harness. You should be able to follow the cable to the left (in the picture) and find that it turns into a yellow cable leading to the O2 sensor on your cat pipe.

The harness is attached to a bracket with a small plastic anchor. Use pliers to squeeze the anchor and you can free it from the bracket.

To the right is a special zip-tie that anchors to another bracket. More on that later.

Once the harness is removed, you can push away the rubber sleeve to reveal the tab for disconnecting the wiring harness. It will probably be tight but it will come loose.   

Here is that other zip tie anchor I mentioned. It holds multiple wires so I didn't want to cut it. Instead I found that the zip tie actually has a little tab that you can hold to release the "tooth" that keeps it tight. I used my pocket knife to hold this tab and then I could loosen the zip tie and remove the O2 sensor wire. Then I re-fasten it to keep the other wires secure.

There is one more zip tie farther up that you will need to release in a similar manner. This will allow you to free up some slack that is needed since the new cat pipe has a different location for the O2 sensor.

Now, follow the yellow wire back to the O2 sensor again and you will see yet another special zip tie anchored to a bracket. This zip tie isn't needed so you could cut it, but I did the same thing that I did with the others by holding the tab and releasing the zip tie. I found that the anchor is hard to remove so I just left it there.

Now that your wires are taken care of, you can undo the two bolts holding the cat-pipe to the down-pipe. One of these nuts was badly corroded and I stripped it. Here is where I used a vise-grip to get a nice tight hold of the nut, then I used my breaker bar on the bolt side and managed to break it free. Once the bolts are removed, slide the cat-pipe off of the J-bracket and remove it.

With the cat-pipe gone, the only thing holding your DP on is a 14mm bolt connecting it to the transmission casing.

I had a lot problems with this bolt too, primarily because I couldnt' get a good angle with a socket due to the shielding on the DP. I tried using an extension but only succeeded in stripping the top of the bolt. Argh!

As a last resort, I cut the bracket with a dremel which took about 30 min b/c of tough angles. If you look closely you can see it. It is not a clean cut at all but it did the trick and I could remove the DP.

Once the DP was gone, I now had clear access to the stripped bolt. I took an impact socket and hammered it onto the bolt so it got a good grip and used a breaker bar to wrench it out.   

One final task before installation is to relocate a rubber drainage tube so it doesn't interfere with the new DP. Free the tube from the c-bracket, then you can rock the c-bracket until it pops out of it's whole.

Relocate it to a similar hole a few inches to the right and re-attach the drainage tube there.

Now you can start putting the new parts on.

First, use an adjustable wrench, 22mm open wrench or O2 sensor wrench, remove the O2 sensor from the stock cat and transfer it to the new cat, using some anti-seize on the threads.

Feed the DP from underneath the car, then hang on the turbo bolts, securing with a nut so it doesn't fall off. Then bolt the DP to the turbo from the top. Don't forget to include the heat shield bracket if you will reinstall the heat shield.

Connect the cat-pipe to the DP with the supplied gasket and 17mm bolts. You also need to connect the supplied bracket to the J-hook to support the cat. The bracket will need to be bent a little as it doesn't quite fit.

The easiest way was attach the bracket to the J-hook very loosely with the bolt. Then, I connected the cat-pipe to the DP with the gaskets and bolts, slipping the bracket in as well. Once it was together, then I tightened all the bolts.

Re-attach the O2 sensor harness to the yellow wire you loosened earlier, routing it appropriately so it's not dangling in harms way or too close to the exhaust.

Fasten the wire with zip ties to the harness bracket from before and other strategic locations.

Next, hang the MP from the rubber exhaust hanger.   

Then connect the mid-pipe to the cat-pipe with the donut gasket and the new 14mm bolts and 12mm nuts and the springs you saved before.   

For the muffler, I hung it from two of the exhaust hangers on the right, then connected it up to the MP with the supplied bolts.   

Then I hung the muffler from the last exhaust hanger and checked and tightened all the exhaust bolts.   

Optional: re-install the turbo heat shield. You will need to trim the shield to make it fit. I used tin snips but there are some double thickness sections which needed a Dremel with cut-off wheel. I also ground down the edges with a sanding stone to remove any particularly sharp sections. The red in the picture represents areas I should have cut off but ended up just bending out of the way to make fit.

With the new DP, there are only 4 points left to fasten with the bolts you saved so it shouldn't be too hard.

Disconnect your battery and hit the brakes so the ECU resets, then reconnect everything up and turn her on! It may run rough for a couple seconds but should even out. That's it! You're done!

The first time I drove (along with my TurboXS Short Ram Intake) there was this huge sound of rushing air. I thought I had forgotten to attach something until I realized it was the turbo spooling up. When I let up on the gas, the bypass/recirculator valve was so loud it almost sounded like a blow-off valve.

The "butt dyno" definitely showed some power increases and I found it a little easier to get my tires to squeal during acceleration. My one concern is that it is quite loud. Even though they no longer make the RFL muffler (really f**king loud), I think this is pretty close. Part of me thinks it's a bit too loud, but part of me loves it so unless I have a problem with cops or something, it shall remain.

Note: many people have reported boost creep and fuel cut issues with upgraded downpipes (see this NASIOC thread). With my UTEC I recorded boost up to 17 psi (~2 psi higher than stock) driving at WOT in 4th gear in 75 degree air. That is very close to the danger zone (18 psi is very bad) so I suspect I will have issues come winter (colder air is denser and therefore flows more)

A good tune should minimize the problem but a port and polish of the turbo wastegate may be the only true solution so be warned and know what you're getting into!


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