There's nothing better to compliment your turbo than a free flow, mandrel bent exhaust (well, maybe an intercooler, but I already got one :P). A free flowing exhaust reduces back pressure and lets your turbo spool up a couple hundred RPMs sooner. Depending on how you make it, you can also cut some weight off of your car because factory exhaust systems are usually god-aweful heavy. I jacked up the front of the car and put it on jackstands to get some clearance so I could go under and measure. Because of the way the driveway is laid out, I didn't need to put the rear end up on jackstands because the slight slope gave me ample space to work with. The entire system was made from one and a half 2.5'' mandrel bends from JC Whitney (the other half was used in the downpipe) and part of a 10' long 2.5'' straight pipe I picked up at a local muffler shop.
Here's the downpipe tacked together with some small sections from the mandrel bends to make the gentle curves so it snakes between the car's steering shaft and the transmission. The top part is from the factory downpipe portion that came with the "kit" I purchased. I was told it was 2.25'' but it's just about the exact same size as the 2.5'' piping, so no complaints there. This was done by cutting and tacking small sections of piping until the bends fit nicely so the downpipe wouldn't hit any of the surroundings. This was pretty tough because I had to keep mounting and unmounting the turbo and manifold to take the downpipe off so I could weld it up (bad design, I know) and this along doubled the time it took to make the dp. I didn't want to weld underneath the car, there's something about laying on my back and welding about a foot above me that just doesn't seem too appealing. However, once the bends were done, the rest was fairly easy. I left the stock cat-back exhaust on so I could see how far I had to extend the straightpipe so that it'll reach the cat. I welded a 2.5'' 3-bolt flange (purchased from JC Whitney along with the mandrel bends) onto the end of the straightpipe so I could continue the rest of the exhaust from there. A note on the flanges - they are really large and clearance between the driveshaft and the body of the car will be pretty tight. What I did was grind down the corners of the flange down to the holes for the bolts.
Here's the catalytic converter replacement, those things are huge flow restrictions and turbos hate em. The stock cat is 15'' long, so this is a 15'' straight pipe with the 3-bolt flanges welded onto the ends. It would've been great to use 2-bolt flanges like the stock flanges, but I couldn't find any that were for 2.5'' diameter piping and I couldn't cut my own because I don't have an oxy-acetylene kit or a plasma cutter, hopefully that'll change in the future, no garage is complete without one or the other ;).
And now begins the fabrication of the rest of the exhaust system. This was made with the rest of the bends and straight pipe and some 3/8'' steel rods from Home Depot cut and welded for the hangers. The muffler for this version was a 2.5'' Dynomax Bullet Race Muffler. I don't remember the exact length, but it's straight through with a perforated mid-section for max flow and a little noise reduction. My system follows the factory exhaust route under the differential and up to a right angle into the muffler followed by a right angle out the back of the car. Due to the limited space and the requirement of a rear exit exhaust (due to local laws), making the exhaust system shorter is nearly impossible without exiting out
of the side of the car in front of the rear wheels. This system left a lot of space under the trunk (possible spare tire relocation?) and in my opinion turned out really well. However, after about a week of driving with it, it was just TOO LOUD, I didn't even have to get on the gas to get thing is screaming loud. It turned many heads and drew too much attention, thus defeating the goal of keeping my car a sleeper...
Nothing can't be fixed right? I picked up a louvered glasspack from eBay for only 18$ to replace my straight-pipe cat to help deaden the sound. I also picked up a Summit Racing Turbo Muffler which was also only like 20$ or so to replace the Dynomax Bullet (I don't think this thing could even be considered a muffler). The Summit Racing muffler has 2 parallel, perforated tubes on the inside, and I'm not sure what it's got packed in it (fiberglass?). Getting it to fit in required me to cut my old exhaust after the bend under the differential and making a really wierd bend so that the muffler would sit in the stock spot and use the stock hangers. The 3/8'' steel rod was used to make hangers again.
These are the pics of the new system mounted. It doesn't extend nearly as far out the back as the old system did, which is VERY bad. I ended up getting this black residual crap around the exhaust cutout :( . I didn't have a tip to weld on so it's on the to do list when I'm at home again. All in all it sounds GREAT. It has a really nice deep tone and has a loud growl when I get on the turbo. At idle it sounds just like the stock exhaust, just a little deeper. I tried to get some videos of the exhaust at the August AutoX but the camera's tiny mic couldn't pick it up very well.