First I want to say this is not going to be a short write up on swapping the EJ203 into a 2.5RS. This is a step by step guide as information on this swap is crazy hard to find.
I own a 2005 Subaru Impreza 2.5RS. I noticed one day while driving that the engine started knocking and making noise. The diagnosis ended up being a spun rod bearing. So therefore there are 2 choices. Rebuild or swap. Rebuilding would take a lot of time and money due to machining, lots of new parts, etc. so I decided to swap. There are 2 engine options for this swap. Either swap another EJ253 SOHC or the EJ203 SOHC swap. I went with the EJ203 SOHC from JDM Racing Motors in Montreal, Quebec. The EJ253 was 1800 from another place and the EJ203 was 1150$ from JDM Racing Motors. The prices includes shipping and are in Canadian dollars however, all prices on their website is US and they ship to nearly anywhere. This thread is a full swap guide with pics and I will do my best to put it step by step to make it simple. This swap is fairly easy providing you have some knowledge on how to work on cars. The entire swap took 5 hours to pull the engine and about 6 hours to put the new one in. Could be done in more or less time depending on experience level. Click on pictures to make them bigger.
You need to re-use all the bolts from the USDM engine. I suggest putting them in a bag and mark the bag to not lose any.
EJ253 makes 165 HP
EJ203 makes 155 HP
New parts ordered
- clutch kit (includes flywheel bearing, release bearing, clutch and pressure plate).
- Intake and exhaust gaskets
Flywheel 53ft lbs
Flywheel adapter plate 50ft lbs
Clutch pressure plate 15ft lbs
Intake manifold 18ft lbs
Exhaust manifold 26ft lbs
To engine 26ft lbs
To cross member 63ft lbs
To start things off, put the front of the car on ramps. Easier to access everything. Remove the battery to ensure that there is no chance of shorting anything out (10mm).
1) Take the hood off. Makes it easier to access everything from front to back. (12mm bolts).
2) Take off the air intake, filter box and tubing. Disconnect mass air flow sensor and the hoses from the head to the intake box. (One per side)(12mm bolts)
3) Drain coolant and engine oil (17mm drain plug for oil). Drained coolant from bottom radiator hose by disconnecting it from the engine.
4) Disconnect the fans on the radiator. Remove hoses and the radiator brackets. Remove radiator and set it aside. Also disconnect the 2 hoses on the driver’s side the firewall for the coolant going to the heater core inside the vehicle.
5) Disconnect the 2 main wiring that connect from the ECU connectors to the intake manifold. They are located passenger side near the strut tower. Also disconnect the O2 sensor.
6) Loosen the tensioners for the 2 belts (the one for the A/C compressor and one for the alternator/power steering) (12mm) and remove the belts. Keep the A/C belt it needs to be re used. The alternator/power steering belt, you can use the JDM belt. (A/C compressor on the JDM has a smaller pulley so the belt is shorter. Does not work with the USDM A/C compressor.) Once that is done, remove the tensioners and set them aside. Makes it easier to remove the A/C and power steering pump.
7) I reused the power steering pump and A/C compressor. A/C compressor must be used as JDM and USDM the connections are at different places. However, contradictory to my research, the USDM A/C and power steering pump does bolt up directly to the JDM engine block. The power steering pumps are the same for JDM and USDM.
8) The power steering pump has 3 bolts, 1 on top and 2 in the front of the block. Remove them and set the pump aside. Also make sure you disconnected the connector to the pump.
9) Disconnect the crank position sensor, cam position sensor, the 4 spark plug wires, knock sensor, and a few other sensors that I am not 100% sure what they are called. And a sensor near the firewall under manifold. The coolant temperature sensor can only be disconnected once the intake manifold is lifted up as it is right under it. Also disconnect the fuel hoses that are located on the driver’s side that connect to the intake manifold. I tied then up with zip ties out of the way.
10) Once everything is disconnected, including the 2 hoses on the throttle body and the hose from the brake booster to the manifold. Before removing the bolts holding the intake, remove the copper tube that connects to the rear of the engine to the rear of the intake manifold.
Remove the 4 bolts on each side of the intake and remove the intake slowly. When I removed mine, I pulled it slowly and disconnected whatever hoses and connections I couldn’t get to with the intake on. Set it aside as you need to re-use the USDM intake for the swap. Be sure that you do not completely take off the manifold until all sensors and hoses are disconnected as you will have to re-wire then if you break them.
11) The A/C compressor has 4 bolts. 2 on top and 2 on the front on the block. Remove the 2 front ones and the 2 on top. The back one can only be accessed once the intake is off. So make sure to take the intake off first. And set the compressor aside.
12) Remove the 3 nuts on each exhaust flange off and the nuts on the motor mounts
13) Remove the 7 bolts that hold the engine to the transmission as well as 2 nuts on the bottom of the transmission. The 2 nuts connect to the guide posts at the bottom of the engine. These are all 14mm and are fairly accessible. The only one that is difficult is the driver’s side nut which is behind the front axle shaft. I used a small breaker bar and the 14mm short socket.
14) Once the bolts are removed, the engine is essentially free. I attached the hoist to the engine using the middle front intake holes and bolts. Hoist the engine up until the engine is just to say supported by the hoist. If you go too high the entire car will lift as the tranny is still attached. I used a hammer and hit the driver’s side top corner of the engine to start to break it loose from then transmission. Once it was loose, use a hammer and flat screwdriver to open the gap all around the engine and separate it. Once it is separated, pull back on the hoist and the engine should come away from the transmission. Hoist it out and set it aside but make sure it’s accessible. A couple parts need to be swapped.
15) I ordered a new clutch kit and flywheel because my old one was finished. However you need to remove the old clutch to get to the old flywheel as the old flywheel has an adapter plate that needs to be put on the new flywheel and also need to press out the old bearing and press in the new one. You also need to re-use the bolts for the clutch pressure plate and flywheel. For the bolts you need a special star socket. Luckily I had it so if you need it not sure where you could find it.
16) Remove the adapter plate from the old flywheel, press out the old and press in the new bearing and install the plate on the new flywheel. Torque it down. I torqued it to 50 ft-lbs.
17) In order to get the JDM engine ready, repeat steps 6 to 11. Set the parts aside because you won’t be re using most of them, however keep them for spares for the future such as sensors, coil packs, plug wires, etc.
This is the JDM engine on the hoist when i first got it.
18) Install new bearing in the adapter and install new flywheel. Then install clutch and pressure plate using the alignment tool on the JDM engine and (flywheel 14mm, clutch pressure plate 12mm) torque down to specs listed above.
19) When I received my JDM engine, the motor mounts were torched off, so remove them and swap them for the motor mounts off the EJ253. They are the same mounts (14mm).
20) Take the 2 clips off on the clutch release bearing and remove the old one. Install new one and put the clips back on.
21) Attach the hoist to the JDM engine and hoist it up. And bring it to the car.
22) Lower the engine slowly to avoid hitting anything. Once in the engine bay, slowly push it back towards the transmission and lower it. I also jacked up the transmission to ease the process of clearing the studs for the exhaust as well as the motor mounts. If you don’t, you will not be able to line the transmission with the clutch because the motor mounts will hit the cross member.
23) Once the engine is close, line up the 2 alignment studs in their respective holes and push the engine back. Once the engine is pushed back ensure it is level with the transmission and the clutch is lined up and push it all the way. If it doesn’t go back fully, use a bolt that connects the transmission to the engine to bring it back slowly and evenly.
24) Re-install all the bolts and 2 nuts that hold the transmission and engine together.
25) Keep the engine suspended by the hoist and take the jack out from the transmission.
26) Install new exhaust gaskets and lower the engine. Make sure to line up the exhaust and the motor mounts. Install the nuts that hold the exhaust to the engine and the motor mount nuts. Torque down to specs.
27) There is only 1 sensor that is different from USDM and JDM. The coolant temperature sensor USDM is 3 wires and the JDM is 2. Swap the USDM from the old engine to the JDM engine. This sensor is on the coolant tube mounted on the top of the block. On USDM, it is facing the firewall. On the JDM, it faces the front towards the radiator.
JDM coolant temperature sensor and location
USDM coolant temperature sensor and location
28) Install the A/C compressor and power steering pump. The A/C has to be installed before the intake manifold however the power steering pump can be done before or after the manifold is installed.
29) Install new gaskets for the intake and install the intake manifold. Reconnect all the sensors, spark plugs, main wiring harness (both of them) and the O2 also re attach the hoses to the manifold and throttle body. Reconnect the spark plug wires. Torque the intake manifold to specs. Also reconnect the copper tube to the intake as well as the fuel lines and the 2 heater core hoses. NOTE: MAKE SURE TO SWAP THE PCV VALVE FROM THE INTAKE MANIFOLD. THE USDM ENGINE HAS THE PCV BUILT INTO THE BLOCK. THE JDM ENGINE HAS IT IN AS A STAND ALONE BETWEEN THE TUBE THAT COMES OUT OF THE BLOCK (SAME PLACE AS THE USDM) AND WHERE IT CONNECTS TO THE INTAKE MANIFOLD.
This picture shows where the JDM PCV valve will be located and connected to the USDM intake manifold.
30) Re-install air intake box, hoses and connect mass air flow sensors. Also reconnect the 2 hoses that go from the heads of the engine to the air box (one each side). The air box I am talking about is the one connected to the throttle body.
31) Re-install radiator, reconnect hoses and connectors for the rad fans and re-bolt the rad support brackets.
32) Add coolant and oil to engine. I was recommended and I highly agree to use Shell Rotella T6 5w40 engine oil with a NAPA gold filter. Will ensure the prolonged life of your new install.
33) Re-install battery and you are now ready to start your new engine. Crank it over a few times. If it starts, turn it off and repeat. I did this to make sure oil was spread around before running it fully. Once I did this 3 to 4 times, I let the car run. Bring it outside and let it run in case there is any smoke. Let it run and check for any lights warnings. Listen for exhaust leaks, ticks, knocking etc. The engine runs good.
The EJ203 max RPM’s are higher than the EJ253. The exact max RPM I am still unsure. I ordered a cable to program the open sourced ECU in the RS. This will allow you to modify max rpm as well as map out your performance and modify many different parameters to get max power. I will be using ROMRAIDER and ECU Flash to do this. I will make another thread once I do the flashing.
Also be cautions if putting a new clutch. Run it as softly as you can for at least 500 km’s to 1000 km’s to allow proper break in time. Last thing you want is to burn out a brand new clutch and have to redo this all over again.
This swap was a new one for me. I have done a few swaps but never a Subaru. I have a friend who knows a lot about Subaru’s and he has a friend who did this very swap so they were very helpful. There is very little info on the EJ203 so I figured I would put it online as it is a great alternative to the EJ253 and direct drop in swap. This swap is also a great way to save money while not losing a ton of HP.
P.S. I took way more pictures than this but I could only upload so many. I will try and upload more when I am able to.
Thanks for reading. if you have questions feel free to ask anything.