In reply to Nitroracer (Forum Supporter) :
The big dividing year on Imprezas is 2007 -- There is a lot of interchange between 1993-2007 for Imprezas, and then 2008 up to some newer date. The WRX is the turbo trim of the Impreza, and the STI is the even faster version. The WRX came with a 2.0l turbo from 2002-2005, with a 2.5l turbo engine after that. The 2.5RS trim features some WRX parts with an NA engine.
The Forester is a lifted Impreza basically (at least for the first couple generations), and that comes in generations of 1998-2002 (the SF), 2002-2008 (SG), and 2009-2013 (SH). The XT is the turbo trim of the Forester.
The Outback is a lifted Legacy, and comes in 1995-1999, 2000-2004 (my favorite), and 2005-2009 (with a facelifit for '08-'09). The legacy follows the same generations IIRC. The Outback (and Baja) were available in XT trim with a turbo 2.5l from 2004 on, the 2.5l turbocharged Legacy GT became available in 2005.
For engines, the big differences are between the DOHC and SOHC, NA and turbo.
The DOHC NA 2.5l engine was phased out with the last of the '99 Legacies, and has a poor reputation for head gasket problems and generally bad serviceability (on all DOHC I know of spark plugs are a 2hr job due to being buried in the valvecover which is itself only 2" from the frame rail. On turbo cars, using the OEM plugs at stock power will last you 60k miles. It's inconvenient, but not the worst.).
The SOHC NA 2.5l has a reputation for bad headgaskets due to graphite coated gaskets that weren't up to the task being used from the factory -- replacing these with a reputable MLS gasket solves the problem. They tend to fail by leaking externally on the bottom, so it is at least a fairly easy thing to check. Despite the recall for these engines, I have heard from a few places Subaru still includes the same graphite coated gaskets with their complete seal kits. As much as people worry about headgaskets, I haven't actually had them fail that often. We did have two engines seize up in our Subaru however, so I'd put checking the dipstick as a higher priority than worrying about the headgaskets. Due to the boxer layout, or the type of people who own them or what, they tend to leak oil.
The SOHC NA 2.2l has a reputation for being rock solid reliable and saving some fuel over the 2.5l. However, they only made them up to '01, and an overhaul in '97 makes it tricky (and illegal) to swap in the earlier ones. It's the kind of engine thrifty mechanics on Craigslist would seek out.
I'd reccomend finding something cheap with an NA SOHC 2.5l. Stay away from the turbo ones, you don't need that kind of hassle in your life. Get something that's not too rusty, I'd avoid 2002-2007 Impreza wagons, they rust from the inside around the strut tower. At minimum, get a good hand all the way up in the wheel wheel and check the strength of the inside part of the strut tower. Find one that maybe has some records / recent parts you like, and just run it. It's easy enough to pull the engine I wouldn't worry about the headgaskets too much -- The price premium for saying they've been done is not worth it unless you have records showing they used MLS gaskets. Also watch out for the timing belt, it's due every 100k (IIRC). Easy to do on a SOHC, but the parts are pricy when you're also doing the water pump. The Aisin kits seem to be the preferred choice these days, there are some bad stories about Gates kits switching bearing suppliers a few years back with disastrous results. MrSubaru1337 is a former (?) dealer tech who has almost a whole channel devoted to Subaru DIYs and information. Personally, I would have a preferance for the earlier Impreza chassis as they are the lightest and smallest, but others with more experience can speak to what will maximize your competitive advantage.
My very limited experience with rallyx is that the driver makes the biggest difference. When I was 17 or so, I convinced my dad to come with me to a rallycross in my mom's manual 2000 Subaru Outback (Also the first car I ever drove, which explains some of my attachement to the brand). As I recall, 75% of the field were Imprezas, and figure half of those were turbo charged. My friend's 944 broke, so we let him drive the Outback, and I remember that he actually beat at least one WRX and a bunch of Imprezas in our Outback, complete with bumper stickers. The shifter was really sloppy and the syncros of first gear weren't the happiest about it, but it did it just fine and drove home after. At this same event, with my dad in the car, I accidently got it up on two wheels after being too exuberant in a slalom and sliding sideways off course into some grass. There were bits of grass between the wheel and the tire for 6 months after.
