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1995 1.8L Impreza Coupe
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192 Posts
Typically you can just swap your current intake/wiring onto the alternate engine and put it right back in; that solves most of the wiring issues. I don't know what engine you have, or what it's going in; so I can't tell you anything for sure. I will note though, that going from an n/a 2.5 to an n/a 2.0l you're going to have a noticeable power loss.
 

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'96 OBS
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374 Posts
Might need to reuse your compressor and alternator as well. Also, if your PS reservoir is mounted on top of your pump you might need to get a separate reservoir and different PS hardlines and make a bracket for it. Depending on what year car you have you might also need to move your crank and cam trigger wheels (and sensors?) over. What engine do you have now? What year car is it? Are you ok losing 30hp or so?
 

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13 Posts
You CAN put the 2.0 in, but do you WANT to

the EJ251 although not exciting is one of the more powerful NA motors Subaru built. As others mentioned you will lose significant street power and torque as well. The EJ20 really needs a turbo to help it out.
In short, stick EJ25 unless you go turbo. Easier, faster, and probably cheaper if you do it right
 

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'96 OBS
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374 Posts
I mean, there are N/A EJ20s that make more power than an EJ251 (not torque though), but that EJ203 is not one of them. For example, an EJ204 out of an 03-09 Legacy 2.0R should make 180-190hp, but that swap is very far from plug n play.
 

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95 L, 96 OUTBACK
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2,916 Posts
I did this exact thing with my dads outback. He isnt happy with how it runs but he wasnt happy with how it ran with the 2.5L. His makes no power off idle which I think is a function of the ECU chasing the oxygen sensor. That might not be it but something the ECU is doing to make no power.

He also pulls a trailer which makes it very noticeable on the power loss but I would think the difference wouldnt be that noticeable in a lighter Impreza.

What happened to the original 2.5L? If you bent valves you can likely use the block with the 2.0L heads for a compression bump. Though I dont know what head gasket you would need.
 

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Cluster Specialist
1999 Impreza RS - WRB
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504 Posts
Will i need a ej20 wiring harness or can i keep my ej25 wiring harness the only diffrence in the engine is the liters one a 2.5 and the other a 2.0 and the website the engine is for sale on says the engine should fit and that i could use my wiring harness heres the webite SUBARU IMPREZA (1999-2005) JDM REPLACEMENT FOR 2.5L ENGINE - EJ20 SOHC 2.0L
To answer your question:

You re-use your original intake manifold onto the new motor. This includes the harness.

Depending on the year of your car, you may need to swap the driver side cam gear, too.

It's preferable to re-use your original accessories (PS Pump, Alt, A/C Compressor)...unless you know how to install the newer ones into your vehicle.
 
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