Ok it's finally time for someone to break this down into a sticky.
If you are considering swapping engines in your legacy you should know from the beginning it is not as simple as swapping your brother's civic hatch. Mechanically it's not too bad, depending on the extent of what you are swapping (I'll explain this later), but there is a lot of wiring. And when I say a lot, I mean a LOT.
The reason for this is that subaru's use one large wiring harness for the whole car, unlike say a honda which has a harness for the engine and a harness for the car, which you can pretty much splice the connectors and be done. With subarus, you will have to splice the two harnesses together at some point along the way, whether its in the dash or right after the ECU.
Motors
That being said; Mechancially it's pretty straightforeward. Any EJ series engine will bolt to any EJ series transmission, and any EJ series drivetrain will fit into any car that had an EJ series drivetrain in it before. This pretty much means that if you have a post 1990 4 cylinder in there now, you can put any other post 1990 4 cylinder in.
The exception to this EJ series engine rule is the EJ20tt (twin turbo). This mechanically would bolt up, but it was never available in the united states, and therefore the way the turbos are routed makes it impossible to install and have it clear the steering rack on a left hand drive car. If you want to do a right hand drive conversion just so you can upgrade to a single turbo to make any power later, go right ahead. Otherwise, leave these motors for the dune buggy and VW beetle guys.
Common swap motors that WILL fit are:
-USDM EJ20t (US wrx engine)
-USDM EJ25t (EJ257) (US STi engine)
-USDM EJ22t (US 90-94 legacy turbo engine)
-JDM EJ20t, EJ20G, EJ20K (Japanese wrx/sti engines of varying years)
- A hybrid of two or more of these (to be discussed later)
- SDM EJ28sq (Gotcha, I made that one up)
Each of these motors (except the one I made up) has it's own advantages and disadvantages. I'll go into each briefly.
USDM EJ20t -- This is the motor out of the US Impreza WRX. It's 2 litres, and generally makes around 160whp stock. The biggest advantage of this motor is that it's fairly common in this day and age. The WRX has been in the states for 5 years now, and there is tons of aftermarket support for the platform. You can purchase pretty much any motor upgrade for whatever year wrx whose motor you took and use it with the same results. Also, if it breaks, it's easy to find someone who knows how to fix it, and easy to find parts. Just go to your local subaru dealership. Really the only disadvantage with this setup is cost, most of these motors are still pretty new. However, deals are to be had if you know the right people. Also, if you plan to go very high horsepower (400+) You'll have to do a LOT of modification, including possibly swapping the block for something different. If you have the money to do that, you might want to start with a better platform, or a hybrid platform.
USDM EJ25t (EJ257) -- This is the motor out of the US STi. It is rated at 300hp at the crank stock, and is a great motor. You can go to extremely high horsepower levels with the right upgrades. With built internals, this motor has tons of potential. It is also more torquey than the 2 litre motors. It has the same convenience of parts and repair availability as the USDM EJ20t, plus the increased potential. However, the offset is cost. These motors are difficult, and therefore costly, to track down. As said before, if you know the right people this can be reduced, but look to spend around 7-10k for everything you'd want for a swap. Also, the wiring can be a bit more difficult for various reasons, some of which is the transmission, but I'll cover transmissions later.
USDM EJ22t -- This is the motor out of the 1st generation Legacy Turbos (SS's). If you haven't figured out the system by now, this motor is 2.2 litres. The advantage of this motor all comes down to how sturdy the block is. It is a closed deck (not as much coolant runs through the block itself), so the cylinder walls are much more supported. With built internals, this motor can be a real killer, as you can run obcenely high levels of boost without having to have the block sleeved, and if you do, I doubt youd ever ever blow it up, ever. This being said, this motor comes with it's share of disadvantages. First and foremost, they stopped making the legacy turbo in 1994. The engine is old, and so are the cars they come out of. They are difficult to find, and even more difficult to find ones that arent high mileage or broken already. Therefore, if you go this route, plan on at least doing a basic rebuild. Also, this motor is not OBDII in and of itself. That makes things interesting with wiring if you have to pass emmissions. Lastly, the heads don't flow well, the turbo is wimpy, and the transmisions will have just as many miles as the motor. More on this in the hybrid motor section.
JDM EJ20G -- This is the JDM v2-v3 STi motor. Similar in many ways to the USDM EJ20t in terms of parts interchangeability (by NO means the same, but similar). The wiring is interesting, because you have to decipher JDM wiring diagrams, but it can be done, and isnt that much harder than a USDM swap. You run into the same OBDII problem with this motorset. The largest advantage of this setup is that the EJ20G is also a closed deck block, only 2 litres instead of 2.2. The best way to do this swap is to find a JDM STi front clip, and get everything, so you don't have to worry about tracking down little parts you need for an already pulled motor.
JDM EJ20K,t -- This encompasses the remainder of the JDM STi and WRX motors. Power levels vary a bit, but its all pretty much an EJ20. All the same disadvantages as an EJ20G, with no sealed deck. Good motors, good turbos, fun out of the box, and inexpensive. Plan on taking your time with the wiring, or you'll regret it later.
Hybrid motors -- Basically, this is what the name says. You take two or more of the motors from above, and combine the parts you want. This requires more knowhow in terms of engine building, as you have to deal with changing compression ratios with different heads and ECU tuning, but its definitely worth it if you have the cash to do it right. One good combination is to get everything for a WRX swap, and use the EJ22t block with the WRX heads, turbo, etc. You can use an STi turbo with any of the above platforms, really whatever you want. As I said though, this requires more mechanical knowhow.
Transmissions
4EAT automatic -- I don't have much personal experience with this transmission, however I do know it doesn't handle much aftermarket power well. You also have to find a motor or ECU for your motor that had an automatic in it before, you can't get a manual ECU to work with an auto tranny as far as I know. Luckily for those of you who would want one (i havent met anyone yet, but im sure they exist), the USDM and JDM WRXs came in automatic form.
5 speed manual -- This is the standard 5 speed manual that subaru puts in most everything. If you have a 5 speed, chances are its built off of this platform. The strength of these transmissions, ive discovered, is all pretty much the same. Different gear ratios, rear end ratios, etc, all make a difference when putting a motorset together, but for the most part they are all the same. The exception to this (There always seems to be one haha) is the JDM STi 5 speed, which was available with the DCCD. This transmission is stronger than the regular 5 speed (Cryo treated gears). It also has the variable center diff (DCCD), which can be wired in to work if you get it with a front clip, or even a pulled motor with all the stuff.
6 speed manual -- USDM STi trans. Much more sturdy than the 5 speeds in any form, plus the DCCD. Don't be mistaken, its still a subaru transmission, you can still break it. Wiring the DCCD in can be a pain, especially if you are putting this in without the rest of the STi stuff (ie on a hybrid motor).
Dash/subframe swaps
The "I'll explain later" parts above are explained now. It is possible to swap the dash, subframes, suspension, gas tank, hubs, etc into your car, with some modifications. If you are more mechanically inclined and would rather spend the extra money on these parts and not do nearly as much wiring, it is definitley worth it. I had it done this way on my GC8 swap, and am extremely pleased. You avoid all the wiring harness splicing because you simply remove the old harness out of the car and weave the one from the donor car in, lock, stock, and barrell. You splice taillight connectors, window switches, and the like, but if you cant do that you shouldnt be doing your own engine swap to begin with. However, be prepared to do a lot of modification to make the dash fit, modification to make the subframes fit, shimming the control arms, switching driveshafts, re-assembling emmissions systems in the gas tank, etc. It is a LOT of work mechanically, and is in no way easier than doing the wiring. It's just as hard, just hard in a different way haha.
Let me know anything that should be added to this, I want it to be helpful so people don't ask the same questions every time hahaha
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Originally Posted by Dinka
