DIY : Turbo Swap Info

[John]

TURBO FAQ


I've seen and answered countless questions online about turbo charging a non-turbo Subaru vehicle. Hopefully this helps clear up some of the mysteries about it. I wrote this quite some time ago to post on a Legacy site....so most of this information is directed towards older Legacy owners, but it crosses over to the other years / models too.


If I have missed anything, please feel free to suggest something for me to add to this FAQ. I will edit it as I see fit.


Wiring Harness Merge - HOW TO


Can I turbo charge my Legacy?

Short answer is no, you can not. However, keep reading and I will explain ways that you are able to have boost in your car.

Why can't I turbo charge my car?

I can go on for days explaining this. However I'll try to keep it short and to the point. The EJ25D is an open deck engine. It is NOT a strong engine and does not handle boost well. There have been people who have been able to run about 4 - 5psi on them though. This is typical for a TD04 turbo, and to be honest isn't enough power for the money you will spend doing it. You also run into other problems like weak internals and compression ratio. The EJ22E is a little bit of a stronger engine and can handle about 10psi, however the money thing comes into play here as well. You can do a swap for just a little more then it will cost you to boost your EJ22E and have considerably more power.

What about the JDM second generation Legacys? They are twin turbo!

Unlike our USDM Legacys, the JDM Subaru Legacy has an engine designed to withstand the extra power of the turbos. The EJ20R has forged internals, and VERY good heads...

I've seen Legacys online that have a turbo. How did they do it?

Most people do some kind of WRX or STI swap. This includes just about all of the WRX / STI guts. Engine, transmission, rear diff, ecu, wiring, subframe, etc. I'll go into more details later on.

What other options do I have besides a WRX or STI swap?

There are a few other options out there. Most of the JDM drivetrains can be bought on Ebay for a reasonable price. Personally, I'm running an EJ20R setup with a stand alone ECU. You can also use the older USDM Turbo Legacy engines.

What about my transmission?

The 4EAT and the 5MT are not strong transmissions. They do excellent under stock horsepower, but when you start adding the power of forced induction to them...they don't last for very long. They may work for a little while, but they will have severe problems A LOT sooner then then should.

So if my transmission isn't strong enough, what should I do?

The easiest thing to do is to find a wrecked donor car. Or you can find a transmission / rear diff combo online. I'm currently running a JDM STI v3 5 speed with a stage 1 clutch. Its good up until about 400awhp.

What about my exhaust? I've installed a turbo engine and I can't make the exhaust fit around the subframe. It looks like I have to cut part of it out!

Our stock subframes were not designed to accomadate for the turbo exhaust. The work around for this is to either use an 04 STI or any 02-07 WRX subframe. DO NOT cut your stock subframe. It will not be as strong as it needs to be if you do this. You can also run any of the USDM turbo Legacy subframes.

So can you just give me a quick list of the parts I need to do a turbo swap?

This depends on what route you go. If you do a WRX / STI swap, you will need the following

• Engine
• Transmission
• ECU
• Wiring
• Rear Diff
• Turbo
• Exhaust
• Subframe
• Custom Driveshaft

If you do some kind of JDM swap, you will need all the same stuff listed, except you will not be able to run a stock ECU. With a JDM swap, your best bet is a stand alone ecu system like AEM or Megasquirt. Piggyback systems are an option, but are more trouble then its worth.

So I did a JDM swap with a stand alone ECU, but my car doesn't run right. What do I do?

You need to get your car dyno tuned at this point. Every ECU has parameters and settings for the engine to run within. With any kind of stand alone ECU, you have to "tune" these settings to your specific setup. Its not hard to do, its just hard to get it right. If you screw up when you do it, it will cost you your engine. If you really did a swap and didn't know the answer to this, you should probably build model cars instead.

I want to do a swap, but I'm concerned about my stock axles. Will they be able to handle the extra power of a turbo engine?

You should be fine within reason. You're not going to be able to put 500awhp to stock axles, but the 200awhp area is fine on stock Legacy axles. A decent upgrade is STI or WRX axles. They are able to handle a little more abuse then the Legacy parts.

I want the EJ20R twin turbo JDM engine in my car! It will bolt right up....right?

Wrong. Its VERY difficult to run the twin turbo setup on our USDM Legacys. The reason for this is the difference between right and left hand drive. Our steering linkage, brake booster, etc gets in the way of the second turbo. I have seen a USDM Impreza run the twin turbo EJ20R, but they had to heavily modify it. My personal EJ20R has been converted to a single rotated turbo. I HIGHLY recommend the EJ20R because its an excellent engine, but expect to NOT have a twin turbo system with it.

So whats the hardest part about doing a turbo swap?

The wiring in our cars is a nightmare. If you do a WRX / STI swap with the WRX / STI ECU, you have to "splice" the stock Legacy wiring harness, and the WRX harness together. If you run a stand alone ECU, you will have to make a custom wiring harness. Trust me, there are A LOT of wires.

I chose to do a WRX / STI swap, but I want a little more power out of the stock WRX / STI drivetrain. What can I do?

Before you start upgrading the stock WRX / STI setup, you should look into some kind of piggyback system like a CobbAP. This way, you're able to tune your car to whatever mods you have installed and get all the power out of it. After a piggyback, you can do a rotated turbo setup with something bigger then the TD04 or VF39. Bigger injectors, exhaust, MSD, boost controller, etc are all good upgrades.

I always look on my local Craigslist classifieds for a wrecked WRX / STI, but I never see one. Where can I find one at?

The best places to look are local Subaru forums, ******, and car auctions.

I want to use X block with X heads for my turbo build. Can I do this?

YES! This is whats known as a "hybrid" build. Usually, you can pair any EJ series head with any EJ series engine. I would recommend using ARP head studs if you plan on running a lot of boost.

I'm going to install a WRX engine, but I want to use the STI 6 speed transmission. Is this possible?

Yes it is. Just like the heads, you can mix-match engines/transmissions. Transmission mounts may be different for each transmission however. The STI 6 speed has the DCCD that will need to be wired in though, and I'm not sure how to do it...but I do know that it has been done on our cars.

Can I use my stock Legacy clutch?

Probably. I would suggest otherwise though. It will likely shatter on launch or slip under power.

What about gas mileage after a turbo swap?

Your gas mileage will suffer some. I know our cars are not the most fuel efficient cars on the road already....but any time you add more power to a vehicle, it gets worse gas mileage. My Legacy turbo isn't THAT bad on gas. The worst part of is is that I have to run 93 octane.

What else do you suggest?

I suggest some suspension and brake work to be done with your swap. If you're anything like I am, you take advantage of the AWD system and haul *ss through the corners. Now that you have more power under the hood, you're going to be able to come into these corners a lot faster. Better suspension and better brakes are a MUST. I have WRX brakes and D2 Racing coilovers. I'm pretty happy with the suspension, however I am wanting to upgrade the brakes even more so then they already are.

What is your current turbo setup?

I have a 1995 Subaru Legacy L. It has the JDM EJ20R engine in it paired with the JDM STI v3 5 speed and a limited slip rear diff. I have a Megasquirt stand alone ecu, port/polished heads, 252 cams, upgraded fuel pump, MSD, 660 injectors, front mount intercooler, rotated TD04, full 3 inch turbo-back exhaust, etc. I'm happy with my current setup, but its only good up until about 400awhp.

There isn't much space under my hood. Are you sure all this turbo stuff will fit?

Yes it will fit

Mechanically, you can bolt up any EJ series engine to any EJ series transmission, and drop the two into any car that was designed with any EJ series engine.

The exception to this EJ series engine rule is the EJ20R (JDM 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.

This is true, however you can use the EJ20R on left hand drive Subarus if you convert it to a single turbo setup. This will require using any stock or aftermarket WRX exhaust. The twin turbo setup does not fit around our left hand drive steering rack and linkage. It can be made to work with heavy custom modifications though, but doesn't seem to be worth the trouble.




The following is a list of Subaru EJ Turbo Charged engines that are able to fit into the second generation Legacy / Outback / Impreza


2.0L Single Turbo

-EJ20G JDM 93-96 STI, WRX 92-96
-EJ20K JDM 97-99 STI
-EJ205 JDM 99-01 WRX Wagon, 01-11 WRX, USDM 02-05 WRX
-EJ207 JDM 98-11 STI

2.0L Twin Turbo must be converted to single turbo

-EJ20H JDM 93-98 Legacy
-EJ20R JDM 96-98 Legacy
-EJ206 JDM 98-03 Legacy
-EJ208 JDM 98-03 Legacy

2.2L Single Turbo

-EJ22T USDM 90-94 Legacy
-EJ22G JDM Impreza STI GC8

2.5L Single Turbo

-EJ255 USDM 06-11 Impreza, 04-11 Forester, 03-11 Legacy, 04-06 Baja
-EJ257 USDM 04-11 STI

- If you turbo your existing engine, it'll probably break.


- If you turbo your existing engine, it'll probably be slow.


- If you plan on doing a full swap, just buy a rolled STi. The end result will be much cleaner, much more reliable, much more durable, and much faster than any piecemeal hodgepodge you put together otherwise. If you REALLY want to have a turbo second-gen that you could actually consider marginally reliable, this is pretty much the best way to go.


- If you DO plan on doing a WRX swap (EJ20 from a USDM donor), set aside funds to replace the EJ20 short block. Stock EJ20 heads on a stock STi shortblock with an 18G is a simple recipe for TONS of torque and lots of fun.


- If you are going to do it, don't skimp. You'll regret every corner you cut when the car breaks down.

A good read about swaps http://www.modified.com/tech/0403scc...ine/index.html