I just completed my first attempt at installing a full turbo back exhaust. I chose to use a complete Cobb system because of the great customer service I have experienced with the company and it was by far my favorite sounding exhaust.
I wanted to share some insights unique to older wrx's that I came across during my install that I was not aware of during my pre-install research. For reference I have an 04 wrxgon that is 99k young.
-The first thing you should know if you are going to attempt this install on an older wrx is that most, if not all, of the parts that are prone to corrosion will be rusted. This includes all of the bolts and nuts, aka everything you need to loosen and remove to swap your exhaust. These parts, depending on the care you have taken of your wrx and the area you live in might even be so badly corroded that they are significantly weakened.
- This being said, some sort of penetrating oil like PB Blaster, Liquid Wrench, or Kroil are mandatory. WD-40 WILL NOT DO THE JOB. I recommend putting your car up on ramps the night before and soaking every bolt and nut that you will need to remove. Even after two applications of PB BLaster, I still managed to over torque 3 badly corroded bolts and break off the heads. I broke two off of the heat shield and one of the two that joins the downpipe to the midpipe. If this happens to you dont panic, these bolts are replaceable as long as you can make it to a hardware store to pick up some stainless steel replacements that are equivalent lengths and thicknesses. I got mine from Lowes. The heat shield has nuts welded on the backside so you will have to drill out the offending portion of the broken bolt or just grind it off and start fresh with a new one.
- The bolts that you need to be the most cautious about are the three studs that extend from your turbo. They are the beefiest of any you will be dealing with and the least likely to have succumb to corrosion but on the off chance you happen to round a nut or break the bolt, your install will come to a standstill until you can replace said stud.
- Buy replacement gaskets BEFORE you do this job. Your gaskets may look in decent shape but remember that they have alot of miles on them and this is a one time cheap investment to ensure a good seal. You will need three with a full Cobb TBE. You will need the Turbo to Downpipe gasket, the 3 inch Downpipe to midpipe donut gasket, and the 3 inch midpipe to catback gasket. I chose to use Grimmspeed for the downpipe and catback gaskets because of the quality, price, and speed of shipping. In the other exhaust install guides and recommendations on scoobymods and Nasioc, mentions are made that you can reuse your donut gasket. At 99k, my donut gasket was mush and fell to pieces when I separated the downpipe and midpipe. You can order them from your local Subaru dealer or Rallysportdirect as even Cobb recommends you use an OEM replacement.
-You will most likely not need to replace your exhaust hangers. This is easily determined prior to your exhaust installation by inspecting them for wear and trauma.
-Your O2 sensor may be very tough to remove while the old exhaust is still on the car. Just unclip it from the connector and cut the old plastic zip tie holders. It is way safer to cut the hanger plugs away from the frame and pop out the hangers than it is to attempt to cut the ziptie from the sensor wire. If you go this route you can use an ordinary box wrench to remove the sensor(plus a weeee bit of PB blaster etc.) instead of an O2 sensor tool. Another option and the route I took was to use a line wrench which I picked up cheaply at a pawn shop. I was the perfect tool for this application.
I followed this excellent guide from Scoobymods. http://www.scoobymods.com/cobb-tunin...26.html?t=4026
It will walk you through the process and answer most noob questions that you will have. Good luck!