My Subaru Engine Swap Project

 Introduction:

 I purchased this 1999 Subaru Impreza 2.5RS in 2003 with 48thousand miles. Less than 40thousand miles later the engine spun a rod bearing and started showing severe rod knock. With a blown engine, the choice was to either purchase a new car, or repair this one. I decided that I liked the car too much to let it go, and went about trying to find a way to fix it myself, cheaply.
 I was shocked to find that prices for the EJ25 engine (the original motor in the car) are roughly as follows:
$4500 New
$3000 Subaru Remanufactured Longblock
$2995 Rebuilt
$600 - $1600 used (60 - 100k miles)

 Disappointed with the engine, and shocked with the prices, I decided it was time to think outside the box and and drop in a REAL engine in the car. Something that would not only last a lot longer than my old engine, but also make my car really, really fast.

 The EJ20 Engine and JDM VS USDM:

Since I wasn't about to replace a used blown engine with another, identical used engine, and there was no way around spending a couple thousand dollars whichever way I went about this, I decided I needed a stronger powerplant. Subaru has been developing their 2 liter turbo engine for many years now (the 2.5 liter naturally aspirated engine has far less development behind it). In the US, the 2L turbocharged design found in the 2002 - 2005 US WRX makes a very respectable 227 Horsepower. However, in Japan, a very similar iteration of this block makes 280HP out the door, totally stock. This is accomplished through a larger turbo, better flowing heads, different cam profile, different injectors and better internal components all around allowing more boost, sooner and making better use of the available fuel (Japanese engines are made to run on what is roughly the equivalent to 95 / 96octane in the US).
 Swapping in a US WRX engine into a non WRX car will net a car that is perfectly compliant with emissions testing, but the engine's complex wire harness will require a professional 45 hours of installation, at a cost of about $4000 from a tuner shop.
 Swapping in a Japanese (JDM) engine, however, will not only be much easier (as the wiring harness is smaller, simpler and separated from the rest of the car), but it can also be done cheaper and make 53extra horsepower STOCK. The downside is that there is no such thing as OBD2 in Japan, netting such a swap an instant fail at most computerized emission tests.

Since there is no emissions testing where I live,  the JDM (Japanese Domestic Market) engine was my first choice. I was lucky enough to find a 1999 JDM engine, which simplifies the wiring job somewhat as most of the connectors will be the same and the fuse box is also the same.
 The engine I found is a 1999 EJ207 JDM WRX Type RA (Race Altered), engine code "EJ207DW1KE". Specs are as follows:

 Turbocharged 2-Litre 4 cylinder boxer engine. VF29 Turbo running 15PSI, 8-1 compression.

Factory Specifications: 280HP@6500rpm, 260ft torque@4,000rpm, redline 8250rpm.

 Here is a comparison between the old engine and the new one:
 

	Engine Code	Displacement	Compression	Boost	Horsepower	Torque	Redline
Stock	EJ25	2.5L	9.7:1	0	165	166	6250
New	EJ207	2.0L	8:1	15PSI	280	260	8250

 Interestingly enough, virtually all Subaru engines are interchangeable: Mechanically, this engine will bolt right up to my Chassis needing only the turbo front crossmember from the donor car... The electrical side of it, however, is a different story...

 Wiring Harness.

All modern engines are run by a Engine Control Unit (ECU). The ECU monitors all engine parameters (air intake, air fuel ratio, exhaust gases, crank position, knock, oil / water temperature, etc) and controls all aspects of the engine (idle / fuel cut, governor, injector duty cycle, air fuel ratio, etc). It also receives data from the rest of the car (ignition, air conditioning, alarm) and outputs data to the dash and elsewhere. As a result, there are a LOT of wires coming in an out of the ECU.
 Unfortunately different engines use different ECUs (and some times even the same engine uses different ECUs) and the differences between the ECU of a turbo car and that of a non turbo car can be quite significant.

 So, in order for the Japanese motor to work inside my US car, I need the Japanese ECU and the Japanese wiring harness. It is on the picture to the left.
 Fortunately even though the bulk wiring harness consists of hundreds of wires for virtually everything electrical on the car, I am only concerned with the engine control part of it (the engine harness). Everything else has to go. In order to do that, the harness is first split:

 Then all the ECU wires are traced to their end, bundled together with tape and tagged out on their end connectors:

 And all unnecessary wires are cut off. There are considerably more non-ECU related wires in the car than engine harness wires.

 This leaves us with JUST the engine harness. This is all the ECU needs to control the engine:

 This required 7 hours of SOLID work. The process was as follows: Once all the wires were free, I held on to all the wires coming from the ECU plugs and taped them together. I kept taping all ECU wires together as I separated them from wires that did not go into the ECU until all wires had been run into their respective plugs. There, I tagged all the ECU wires out, then cut and removed everything that was not ECU related. The reasoning behind this is simple: If it does not go into the ECU harness, then it is going into the rest of the car. Since all I am replacing is the engine, there is no reason to replace any of the other wires. It was not difficult, but it took a very long time, and a LOT of focus and discipline.

  I do not believe this swap would be possible without a wiring diagram; the wires going into the ECU from the dash and fuse box go into plugs that do not necessarily correspond with the RS plugs, so I can neither use the JDM harness on the dash (nor would I want to: THAT would be a wiring nightmare) nor figure out from just the plugs which RS plugs correspond to it. With both the RS and the JDM wiring diagrams I can simply pull the dash wires from the RS ECU and splice them into the JDM ECU though. Much easier.
 Only two plugs in the engine harness are different: AT/MT neutral position switch and MT/AT identification (I reused those). 4 wires leave the engine and do not go into the ECU: Those are Ignition power (red/yellow), Ground (black) and the a thin red/white and a red/green one. Those go into the dash.
 Below, for comparison purposes, is the stock 2.5RS ECU (left hand side) and the JDM ECU. Notice how the plug size, shape, and pin geometry are all different. The mounting points are also mirror images of one another (RHD issue).

This is the ECU identification. AE480 = Version 5 WRX Type RA.

In-Car Wiring.

 With the AC unit out the rightmost firewall feed through is pushed back into the passenger compartment and the wires going from that engine harness to the ECU are cut. Anything specific to the 2.5RS engine can be removed, anything coming from the fuse box, the dashboard, the fuel pump, relays, etc has to be spliced into the JDM harness. I made the pinout matrix below to make my job easier; every sensor/connector is named, identified, and put next to its plug location on the JDM ECU:

Content	Type	2.5 RS Plug	2.5 RS Connector	JDM Plug	JDM Connector
Crank Pos Sensor	Signal (+)	B135	1	B136	5*   or 6
Crank Pos Sensor	Signal (-)	B135	8	B136	23
Crank Pos Sensor	Shield	B135	10	B136	30
Cam Pos Sensor	Signal (+)	B135	2	B136	6* or 7
Cam Pos Sensor	Signal (-)	B135	9	B136	23
Cam Pos Sensor	Shield	B135	10	B136	30
MAF	Signal	B136	5	B136	1
MAF	PSU	B136	15	--------	-------- --------
MAF	Shield	B136	25	B136	30
MAF	GND	B136	8	B136	31
Throttle Pos Sensor	Signal	B136	17	B136	20
Throttle Pos Sensor	PSU	B136	15	B136	12
Throttle Pos Sensor	GND	B136	16	B136	24
Front O2 Sensor	Signal (+)	B136	7	B136	21
Front O2 Sensor	Signal (-)	B136	20	--------	-------- --------
Front O2 Sensor	Shield	B136	23	B136	30
Rear O2 Sensor	Signal	B136	18	--------	----------------
Rear O2 Sensor	Shield	B136	24	--------	----------------
Rear O2 Sensor	GND	B136	16	--------	----------------
Front O2 Sensor Heater	Signal 1	B134	22	--------	----------------
Front O2 Sensor Heater	Signal 2	B134	23	--------	-------- --------
Rear O2 Sensor Heater	Signal	B134	21	--------	-------- --------
Engine Cool temp sensor	Signal	B136	14	B136	28
Engine Cool temp sensor	GND	B136	16	B136	24
Vehicle Speed Signal		B135	24	B135	26
Starter Switch		B135	28	B135	2
A/C Switch		B135	27	B135	11
Ignition Switch		B135	7	B136	25
Neutral Pos switch MT/AT		B135	26	B135	29
Test Mod Connector		B135	14	B135	22
Knock Sensor	Signal	B136	4	B136	26
Knock Sensor	Shield	B136	25	B136	29
AT/MT Identification		B135	25	B135	4
Back Up PSU		B136	9	B135	17
Control Unit PSU		B136	1	B136	9
Control Unit PSU		B136	2	B136	8
Sensor PSU		B136	15	--------	-------- --------
Line end Check 1		B135	20	--------	-------- --------
Ignition Control	#1, #2	B134	25	B134	7
Ignition Control	#3, #4	B134	26	B134