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I stole this from another site,,it is great information.
Alot of people ask about converting to Subaru, so I'm going to attempt answering what I know about this subject. I've had lots of Information on the Subaru's and because of my age and time I have I want to post as much as I can here in hopes it will help someone. I am happy to help answering questions, but I am a busy boy trying to build 3 cars before my time runs out. What I'm mostly going to be talking about is the EJ series subaru engines, however most of the principles also apply to other Subaru boxer engines.
What follows is my opinion. I say MY opinion, which is not to say it is the right or only way to do things.
As I see it, the Subaru engine is a modern VW which is on steroids.
Benefits of Subaru power:
Subaru boxer engines are 50 YEARS ahead of air-cooled VW boxers in design and technology.
They run smoother and rev quicker.
They have two more main bearings than a VW and a full flow oiling system.
Standard features EFI, electronic engine management and multiple camshafts/valves per cylinder.
They are plentiful and parts are easily available.
Extreamly reliable.
They are under stressed and so make a great engine for mild to wild performance modifications.
Aftermarket tuning parts available are readly availble.
Dollar for dollar they are cheaper and more reliable than a VW boxer engine of the same capacity/power rating.
Disadvantages of Subaru power:
Subaru boxer engines are a bit heavier due a bigger case, extra oil and water cooling.
Subaru boxers are physically bigger than VW boxer engines, but not really that much.
Parts are more expensive than VW boxers in general.
The oil sump needs modification to be safe in most conversions.
What does a 'Subaru conversion involve?
Depending on weather your doing a Subaru to VW or mid-engine will determine what needs to be addressed
Things that need to be addressed are which engine you'll be using, fuel system, exhaust system, cooling system, engine mounts, Bell housing, flywheel, clutch, ECU and wiring and other bits and pieces.
Fuel system:
Putting a Subaru engine to your VW is going to take some different thinking and needs. as far as your fuel tank goes. I use two pumps. 1 in the tank is a low pressure and high volume and a inline high pressure high volume to feed the injectors. The need to provide fuel to the pump at all times is very important, and to avoid starving them of fuel during hard cornering or acceleration. The fuel needs to be collected in a reserviour.
The tank should have return supply fittings on it and a vapour line fitting. Two extra solid lines are needed to service the EFI system. One is a return line from the engine to the fuel tank. The second is a vapour line that draws fuel vapour off the top of the tank for the emission control system on the inlet manifold. In reality, the best option is to fit two new solid lines for the fuel supply and return and use the old fuel line as a vapour line.. Do NOT use COPPER tube, it work hardens due to vibration and will crack allowing high-pressure fuel to spray all over the place. The tube should be rubber mounted had have grommets around it when it passes through any panel (other wise it will wear through and leak). Running the lines under the car is ok as long they have a guard of some sort over them. Through the tunnel is ok as well. Do not run the lines through the passenger compartment. Don't weld them either, it will lead to localised brittleness and cracking Also, make sure you have good clamps and high-pressure hose between the EFI pump/injectors/return-line, etc.
Filters
EFI demands well filtered fuel. I use two filters. One low pressure one near the tank outlet, and a hi pressure one after the high pressure pump and before the fuel rail.
Cooling System.
If you can use the original one great but chances are you'll be using a different one. Most of my cars use multi radiators. I usually mount one on each side in front of the rear wheels out of harms way.
As for a place to mount the radiator, the best place is in front of the car. You can put the radiator under the car with a scoop to direct air into it. In this set-up it may even be laid flat racing car style. Angling radiators forward when mounting them is also good, as it slows down the air flow and helps it to remove more heat. Have an accurate water-temperature gauge. make sure enough air gets to the radiator to keep it reasonably cool at highway speeds.
I have seen radiators mounted in about every place you can think of and the best one is the one that keeps the engine at operating temps all the time. You'll also need a big fan on the radiator to cool the engine in traffic or on hot days. The fan should NOT be operating continually. This will actually restrict airflow in certain circumstances. It is also a constant and unnecessary drain on the electrical system and only used when needed.
As for hoses and water pipes I used wire to make a pettern and then have tubing of the right size bent and couple the tubing with rubber hoses. Use as little rubber hose as possible. Also try and keep the hot pipes out of the way so no one gets burnt.
Also, don't forget to hook the heater pipes up to each other so the coolent circulates through the system properly. Just blocking them off will make the engine overheat.
Exhaust system.
OutFrount makes headers for the non-turbo and turbo'd engines. Remember, the catalytic converter should be about the same distance from the engine as the standard system is if you want to use the factory ECU. Also, you will need to make sure that the exhaust oxygen sensor is in place and working. After that make it as loud as you like.
For the turbo engine work with a turbo specialist till you get the hang of how it works. If you do go the turbo route be ready to experance the rush of your life.
Engine mounts and bellhousing.
Subaru engine have engine mounts. These need to supported from underneath to mount the engine properly. The standard four engine/gearbox bolts will not hold an EJ properly and You will need to fabricate something to support the engine using the factory mounts in some way. The mounts will need to be solid also. Subaru boxers have a lot of torque and can move around quite a bit.
Bellhousing.
For me this is the easy part. I use the Subaru transmission, clutch and bellhousing as my cars are mid engine cars and use a Bremar adaptor to convert my transmission to a mid engine setup. For everyone else there are a number of companies make good quality conversion kits. Kennedy from what I hear make a good kit.
Clutch
Once again I use the Subaru Clutch with there 5 speed transmission, but Kennedy and Outfront have anything you'll need. My understanding is the Adaptor comes with a flywheel so 1/2 the problem is done.
In keeping with a modern setup I use a hydraulic clutch. Makes installation simple.
Sump.
For most cars, the standard EJ sump will need too be modified, shortened. Outfront and Kennedy sell these, or you can have a shop fabricate you a unit that will do. It's important, not to compromise the volume as this can shorten engine life.
ECU and Wiring Loom.
You have two choices when it comes to ECUs. Both have good and bad points. First using the standard ECU. The standard ECU is a highly developed and tuned computer w/self diagnosis, closed loop functions and smooth operation with no programming needed. The ECU will operate best when the engine is setup as close to standard as possible. What I'm saying is the inlet, exhaust and sensors need to stay as close to original as possible. Also, your pretty much stuck with the factory tune. You'll also need to strip down the factory loom and wire it up properly. For those needing to meet emissions laws this is your only option.
The other option is to use an aftermarket, programmable ECU. Many of these are available as a plug-in unit for the N/A and turbo engines. The tuning possibilities available are infinite, But for the best tune, you really need dyno time and an experienced tuner for the ECU in question. John over at Outfront or Paul here on DBA can help you with your stand alone ECU's
Gearbox and drivetrain.
Which gearbox? Myself I use the Subaru 5 speed transmission in the Mid-engine setup so alot of my problems are solved. I'm also going to the Subaru automatic transmission so I can set it up even better. But for those of you that are going to use the VW transmission, your going to need something with moderate to high strength.
For people using IRS (independent rear suspension) For non turbo engines (EJ20, 22, 25) the 002 or 091 Kombi boxes are strong enough in standard form if treated with some respect. These are ideal for offroad work. For road cars the box of choice is the single side-plate Lbug (1303) box with the 3.88 diff ratio. If you want to go drag racing you will want a super-diff and maybe different ratios, but this box is a great place to start.
For turbo engines (EJ20t, EJ20tt), plan on spending some money. No standard VW box will handle 200hp for long, and all EJ turbo motors make more than 200hp stock. Using one of the gearboxes mentioned above, with all the tricks here apply. Hardened keys, welded 3rd and 4th gears, strengthened side plate and a super-diff are mandatory for longevity. This will cost thousands of dollars and that is before you go putting special ratios in. That said, once the box is built properly it should last.
Some people prefer Porsche 5 speeds but be prepare to spend big dollars.
_________________  If your clutch ain't slippin,, you probably got it adjusted right!!!!!
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