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Turbo Upgrade 1998 Subaru Legacy GT Wagon

Motor Trend logo Motor Trend 5/5/2015 Mike Sabounchi

We've been making progress on our 1998 Subaru Legacy GT wagon (see the embedded links throughout this post for proof). Now that we have the JDM 2.0-liter turbo motor successfully transplanted and the chassis components installed, it's time to take things to the next level and install some serious parts. We weren't going to be happy with the 190 horsepower that the '05 JDM motor made out of the box, so we turned to our good friends at Garrett and TurboSmart USA to help us breathe a little more power into Project Legacy.

1998 Subaru Legacy GT Wagon Project - BP5 Engine Swap

MotorTend Image© Provided by MotorTrend MotorTend Image First, new up- and downpipes had to be made. We turned to the masterful hands of Ubersport Performance to fabricate one from scratch, and it turned out beautiful. (Note: We went with V-band clamps on all piping. Not only will it ensure a proper fitment, but it will allow us to upgrade our components at anytime if need be.)

1998 Subaru Legacy GT - Suspension Upgrade

MotorTend Image© Provided by MotorTrend MotorTend Image As you can see from the double openings at the top of the up-pipe, we are going for an external wastegate setup. Without gettin' too technical, the main reason is simple:
1. We don't have to worry about plumbing a wastegate through our exhaust.
2. We want to shoot flames out of the wastegate as this death wagon comes screaming down the track under full boost!

Subaru Legacy Depo Headlight & JDM Taillight Install

1998 Subaru Legacy Gt Turbo Upgrade Turbosmart Wastegate© Provided by MotorTrend 1998 Subaru Legacy Gt Turbo Upgrade Turbosmart Wastegate That being said, we couldn't have been happier that we choose to go with Turbosmart on our wastegate/blow-off valve setup. Not only do both components come with all the parts needed to properly weld and install to any setup, but Turbosmart is a local company here in SoCal—if we ever needed to rebuild components, it would just be a quick ride up the freeway to get all the parts we needed.

Subaru Legacy Vinyl Wrap

1998 Subaru Legacy Gt Turbo Upgrade Wastegate Piping© Provided by MotorTrend 1998 Subaru Legacy Gt Turbo Upgrade Wastegate Piping We really wanted to route the piping for our external wastegate out the hood or out of the fender, but we knew that could lead to issues down the line if it were to rain. The safest place to route our wastegate piping was alongside our downpipe.

1998 Subaru Legacy GT Brake & Suspension Upgrade

MotorTend Image© Provided by MotorTrend MotorTend Image After all of our wastegate and up-pipe components were finished; it was time to wrap our DC Sports headers and move on to the intercooler piping and blow off valve.

MotorTend Image© Provided by MotorTrend MotorTend Image We chose to wrap our headers for two reasons:
1. It keeps hot exhaust gases inside the exhaust chambers, which will help spool up the turbo faster.
2. It keeps underhood temps much cooler. (Note: Look how close the headers are to the oil pan. We don't want to risk overheating our oil, especially on a track day.)

MotorTend Image© Provided by MotorTrend MotorTend Image Before any cutting or welding took place, we mocked up our front-mount intercooler in place just to see where all the piping would go. And look at the size of that core! It almost makes us want to run the car with no bumper and go full-blown Mad Max style!

MotorTend Image© Provided by MotorTrend MotorTend Image After we took measurements and got all the pieces mocked up, it was time to build some brackets and secure everything in place. Kelly of Ubersport went to work welding and fabricating, which gave time for us to focus on other things.

MotorTend Image© Provided by MotorTrend MotorTend Image One of the most overlooked areas in every engine swap has to be the wiring. There are too few people who actually know what they are doing that it is becoming more and more difficult to find a good "wiring guy" these days. Since we were going outside of the mold a bit and throwing an '05 JDM Legacy 2.0 GT drivetrain into an older model, we had to bring in the big guns for this job. Our friend Kevin Wentzel from Garage Tuning came to our rescue. The key with any wiring project is to get the ECU pinouts and diagrams from the manufacturer so you can either merge or create a new harness from the factory ECU pin locations. Unfortunately, our motor isn't a commonly used swap, so finding the exact pin locations and wiring information was a major hassle. Eventually, a phone call to our friends at AVO Turbo World Japan got us all sorted out, and they faxed us over the information we needed. Two major elements we wanted to retain for this build was the drive-by-wire manifold on the new motor and the engine's AVCS (Vari

The key with any wiring project is to get the ECU pinouts and diagrams from the manufacturer so you can either merge or create a new harness from the factory ECU pin locations. Unfortunately, our motor isn't a commonly used swap, so finding the exact pin locations and wiring information was a major hassle. Eventually, a phone call to our friends at AVO Turbo World Japan got us all sorted out, and they faxed us over the information we needed.

Two major elements we wanted to retain for this build was the drive-by-wire manifold on the new motor and the engine's AVCS (Variable Valve Timing). Since the '98 Legacy never cmae with these features, merging the two harnesses wasn't a walk in the park and required some extra parts.

MotorTend Image© Provided by MotorTrend MotorTend Image Luckily for us, Garage Tuning has been building Subarus for quite some time and had the treasure chest of extra wiring harnesses and parts stowed away. Once we found all the parts needed to complete the wiring, it was time for Kevin to start making sense of it all.

MotorTend Image© Provided by MotorTrend MotorTend Image While Kevin was sorting out the wiring, we checked back in with Kelly and he had the majority of the intercooler piping welded up, plus the new turbo setup assembled. Just look at those welds on the blow-off valve section! We decided to go with Turbosmart's "Race Port" valve. Aside from it's construction quality being second to none, we really liked how easy it was to change or add different valve springs so we could adjust its sensitivity accordingly, plus it just looks damn cool.

MotorTend Image© Provided by MotorTrend MotorTend Image All this fabrication work would mean nothing if we didn't choose the right turbo for our build. Since our goal was around the 300-whp range, we ended up going with a Garrett GTX2863R turbo.

MotorTend Image© Provided by MotorTrend MotorTend Image The key with this turbo size is that we're looking for 300 usable horsepower—not just one big number at the end of the rpm curve. That's where the GTX comes in. Its new 11-blade billet compressor wheel will spool up faster than previous-gen turbos, and it also has the ability to produce up to 450 hp if we ever needed it. And since we planned on keeping the internals of the motor untouched, we wanted to keep the build as balanced as possible. Yes, we could've slapped on a much larger turbo and went for the "wow" factor on the dyno, but that's not the point. We want this wagon to go fast, but we also want it to last!

MotorTend Image© Provided by MotorTrend MotorTend Image While all the piping and wiring was getting dialed in, it was time to tackle cooling. Let's rewind back to the reason why we got into this swap in the first place was because of a blown head gasket on the original motor. The head gasket was so blown and the motor got so hot, that it caught on fire!

MotorTend Image© Provided by MotorTrend MotorTend Image We weren't going to make the same mistake twice so to ensure proper cooling, Koyo provided us with an extra large radiator intended for a '05 STi.

MotorTend Image© Provided by MotorTrend MotorTend Image This bad boy is massive and will have the capacity to keep water temps at a respectable level in any condition whether daily driving or abused on the track. Not only does Koyo do a fantastic job with the cooling performance of its products, but also the quality of construction is top notch. Just look at those welds! This is the kind of stuff that gives us confidence when pushing a car to its limits.

MotorTend Image© Provided by MotorTrend MotorTend Image Now that the engine and all of its go-fast bits have been sorted out, it's time to prep the car for track time! Stay tuned, because we got some big plans that involve a major makeover. We'll give you a hint...things are about to get a whole lot wider!

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