As I mentioned, I put 2004 Impreza WRX STi suspension on the Legacy. It's quite an improvement over the stock struts and springs from 1993.

Here's a pretty picture of my struts:

 

There is one major issue that comes up when swapping: The rear tops.

Front Subaru suspension has pretty much stayed identical from 1990 to 2004. In 2002, the front bolt pattern in the strut towers rotated slightly. In 2005, the STi front hubs changed. WRX is the same through 2006. I believe Foresters and Legacies are still the same, as well.

The rears seem to change all the time, at random. 90-91 rear springs and tops are different from those in 92-94. 00+ Legacy tops are completely different. The bolt pattern on Imprezas changed in 02. And that is where the issue occurs.

A strut assembly is comprised of, from top to bottom of:

-Strut top
-Spring perch and piece of rubber
-Spring
-Lower spring perch and another piece of rubber

The lower spring perch is attached to the strut body. The strut tube passes through the upper spring perch and strut top, and everything is held in place by a bolt on the strut tube.

This is a picture of an old assembly, without the spring.

You can see how the spring should sit between the two perches. I'd have put the whole thing back together, but I need either a spring compressor or a fat guy to get the spring compressed far enough to attach the top nut.

The three bolts sticking out of the top attach to the body of the car. This pattern is the change that I mentioned.

Unfortunately, the pattern isn't all that changed. I had hoped to be able to just use the STi perches with a set of really nice group N tops that I had bought. The springs and spring perches also changed, so I could just use my tops and perches on the STi springs, as I had originally planned.

Here is the top of the 04 assembly:

As you can see, the top and perch are completely different. Not only that, the top diameter of the spring is different.

At this point, I was faced with a few options. I could try to find some perches that fit these springs, or make the tops fit. I had no idea if there was such a perch, though. Turns out there is. The 90-91 Legacy tops are one piece, and the springs are tapered and have the same top diameter. I could also have bought some 02-03 springs with a similar rate, and used my stock perches and the tops I had bought.

Well, I had my car apart, couldn't get the perches, and had to go to work the next week. I decided to do what a few others had done, and make these tops fit in my perches. I'm getting a little ahead of myself, though, and I should probably go through the basics of changing the suspension.

The struts attach to the car with the three bolts on the top as previously mentioned, and also bolt to the hub of the car. In order to remove the nuts on the tops, you need to open the hood and take out the back seats. To remove the bolts on the bottom, you'll obviously need to jack up the car and take off the wheels and tires.

The rear seats come out pretty easily. There are two bolts holding the bottom in place, and it's hooked onto some little bars on the back. Remove the bolts, lift the front of the seat up, and push it toward the back of the car and lift to get it off the hooks. For the back of the seat, there are three bolts and similar hooks, and you'll also need to detach the trunk carpet from the backs of the seats if the fold down. I also ended up taking the seatbelt winders and some of the interior trim off, because I was having trouble reaching some of the top bolts.

Here you can see one of the bolts sticking out of the strut tower. You can also see some of the crap I took out, such as the back deck.

This is the bottom of that assembly. The black tube is the old strut and it bolts to the hub with two bolts that are behind the brake disc. The bolts were a huge pain in the ass to loosen after not moving for about 13 years and being in Montana where it snows and stuff.

I finally got those out after about a whole day of getting really pissed off and soaking the bolts in PB Blaster penetrating lubricant.

Here's a comparison of the old and new struts:

You can see that the new one is way better because of the cherry red STi color. Also the strut tube seems to be significantly larger. This is because it is an inverted strut. There's actually a smaller tube inside that one, that attaches to the bottom of the strut body. There's a little bolt on the bottom so I could replace the strut tubes if I wanted with something like a koni insert. Some benefits of the inverted design are strength and ease of maintenance. It sure looks stronger, doesn't it?

So, in order to get the 04 rear tops to fit, I decided to modify the strut towers. This actually isn't to terrible, and helps with one of the issues involved in installing these struts. The 02+ Impreza sedans have a wider track than wagons and older cars like mine. So, the suspension geometry is slightly different due to the wider lateral links. Everything else is pretty much the same, except the angle between the bolt holes on the bottom of the strut is slightly different, because the strut is angled toward the outside of the car a bit more. If you simply install these struts on a car, with a narrower track, you will have positive rear camber.

Camber is the angle of the tire with the road. Negative camber means the tire is leaning toward the center of the car. Positive is the opposite. Camber affects tire wear, and handling. A bit of negative camber is good, because in a corner, the car will tend to lean over.  When the car is leaning, the tire is leaning a bit too. The tire will also want to roll over onto it's sidewall. Negative camber will make the contact patch with the road better, and therefore give better grip in a corner. Positive camber will increase the tire's tendency to roll over, and decrease grip on the road. So, negative camber = good, positive camber = bad. Excessive negative camber can cause uneven tire wear and decrease straight line braking ability. The wear doesn't become an issue until you're at about 2 degrees, and braking isn't affected until 3-4.

Back to my struts. The clever engineer in me decided that if I drilled two new holes in the strut tower, I could move the mounting point inward. Not only would the new tops fit, I would lose that positive camber that isn't good. So, I carefully measured where the holes should be, and started drilling. Oh, yes, that looked nice. Then I tried to put the strut top in. Oh, no, that's not very nice. The top wouldn't physically fit into the strut tower any more, because it was hitting the wall. DAMNIT ALL TO HELL!

Only option now was to grab a file and move them out until the fit. I slotted the two internal holes a little haphazardly, and very carefully and evenly filed out the outer holes until the tops fit. This way, I insured that the rear camber would be pretty even from side to side (called cross camber), and that the struts would be wedged securely into the towers.

I must say that's looking a little bit ghetto:

I cleaned up the holes a bit more after that picture. In any case, success, they fit!

They're still mounted a more inwards, as well.

Then all that was left is to attach the bottom:

And then do the fronts.

Fronts were cake because I presoaked the bolts a little more than I had done in the rear, and the entire assemblies bolt in directly.

Well that was easy. Now I'm going to talk about camber a little more.

The camber is only adjustable in the front suspension. That top bolt you see attaching the strut to the hub has a little elliptical cam on it. By rotating the bolt, the camber changes. The rears don't have this, though. I had heard about the possible problem in the rears ahead of time, so I went ahead and bought some aftermarket bolts. Now all I have to do is install them. I am going to need them, too, because I can tell there is some positive rear camber by driving and just looking. It's a very small amount, though, so I should be able to get a fair amount of negative camber with my bolts. At the moment, I still need an alignment. I've needed one for months. I recently bought some new tires, so I'll get one before I put them on. Ride height is also slightly lower, which was a pleasant surprise. I expected stiffer suspension from a heavier car would cause it to sit a little higher.

Impressions:

Wow, the new stuff is awesome. The car handles great, even without a decent alignment or tires, which are very important as far as handling goes. Ride is stiff. Long drives on bumpy freeways start to get tiring very quickly. The springs, with rates of 224 lb-in front and 194 lb-in rear, significantly stiffer than the old ones. The valving on the struts is also very stiff.