Swap City: Part 1

Several months ago, Eddie came to me with a proposition.  He was looking to get a more powerful engine for his ‘03 WRX — which meant a spare stock WRX engine — and he knew I was looking to get a used WRX.  He offered to swap his stock WRX engine into his ‘01 Impreza 2.5RS and sell it to me.  I would get the best of both worlds, the timeless body-style of the GC Impreza, with the internals of a WRX.

Let’s make it clear, though the swap was mainly for the increased power, upgrading other parts of the car to handle the power was essential.  Here’s a list of upgrades that are going into the car:

  • EJ205 engine
  • WRX Downpipe
  • WRX Up pipe
  • Turbo Crossmember
  • Stock WRX Intake
  • WRX Alternator
  • WRX Power Steering Pump
  • Nissan 300ZX Brake Calipers (same as WRX calipers)
  • STi Brake Master Cylinder
  • STi Rear Subframe
  • WRX Rear Differential
  • WRX Rear Axles
  • WRX Driveshaft
  • Cusco Zero-1 Coilovers
  • 17” Rota Tarmac 2 — Gold (of course)
  • WRX Pedal Assembly

By looking at the list, it’s obvious that this GC is going to mean business.  I also intend to take it to the track a few times a year. So after months of gathering parts and waiting for Eddie to finish swapping his ‘03 WRX, it was time to start swapping the 2.5RS.

Day 1

On the first day, Arthur — a friend who volunteered to help out — and I were in charge of stripping the interior of just about everything (seats, center console, dash, and the carpet). Stripping interior was necessary because we’d be completely pulling out the wiring harness of the car and replacing it with one from a WRX, since the RS harness wouldn’t be compatible with some of the upgrades.

The amount of little tabs and screws holding the carpet and dash was infuriating, that was coupled with the fact that we’d be reusing them, so we had to make sure to be careful not break or lose any of them.  A couple hours and numerous sighs later, we had the dash, center console, and all the tabs that held the carpet in — except for one, which gave us so much trouble we decided to move on.

While we were doing this, Eddie took the wheels off, drained all the fluids from the vehicle, and began working on the rear of the vehicle.  First, he took the entire exhaust off, from the headers to the tailpipe.

He then took off the stock rear axles and discovered something quite alarming, the CV joint housing on one axle was broken, exposing the joint and grease inside.  This could’ve been bad, as the joint could have dried out, potentially causing a serious break.  He’s tracked this car in the past, most likely with the tear in the CV joint housing.  Just a reminder for everyone to thoroughly inspect their car every now and then, especially if you plan on bringing it to the track.

Then he started unbolting the rear differential and driveshaft from the body.  The rear diff is attached to a subframe (which would also come off) and also held into place by a plate bolted onto the body.  After he took out the rear diff, we noticed our first major issue of the day.  He noticed the WRX diff didn’t have the 2 studs that allow it to be mounted to the rear subframe.

Transferring the studs from the RS diff to the WRX diff would seem like an obvious solution, and we would’ve done that, if it weren’t for the fact that we were going to swap in an STi rear subframe, and the mounting points for the diff are different.  So off to Lowe’s we went to find bolts to fit in the WRX diff.  After we came back with the bolts I thought would fit, we discovered the threading was different.  It turns out the stud in the RS diff had 2 separate threads; the inside that goes into the diff is different than the outside thread used to secure it to the subframe.  And, of course, I brought a nut that screws onto the outside — the side that doesn’t go into the diff.  After getting the correct threaded bolts, we continued.

Before we could put the WRX diff on, the stock subframe had to come out and be replaced by the STi subframe that Eddie had lying around (this guy is like a Subaru pick and pull).  I’m pretty excited about having the STi subframe back there; when comparing the RS subframe with the STi one side by side, it’s obvious the STi subframe will be much more rigid.

The 4 inserts which are directly bolted onto the body are metal on the STi, whereas they’re rubber on the RS.  Also, the STi one is a double layer of metal throughout almost the entire body, while the RS is all one layer.  The lateral links for the STi subframe were also more stiff, they were a few millimeters thicker than the RS ones; and two of the RS links were just thin, rolled pieces of metal, not solid tubes like the rest.

After we got the STi subframe bolted on, it was time to connect the WRX driveshaft with the WRX diff.  They are connected by 4 medium-sized bolts, a little smaller than I’d think since they go under a lot of stress transferring power from the driveshaft to the diff.  There didn’t seem to be a huge difference between the RS and WRX driveshaft, visually.  Except the WRX driveshaft used a ball joint instead of a pin joint.

Once the diff and driveshaft were connected, we used a jack to raise the diff into place and began bolting it into the rear subframe.

Then it was time to install the WRX axles; first, installing one end to the wheel hub, then shoving the other end into the diff.

After that, we called it a day.  We accomplished a good amount in the 7 hours we worked.

 Day 2

This day wouldn’t be as productive as the previous.  We planned to lift the stock RS engine out and drop in the WRX engine.  However, we couldn’t get the turbo crossmember — the frame the engine sits on — in time, so we just swapped the stock fuel pump for the STi pump.

The fuel pump is located under a plate directly behind the back seat, in the trunk.  There are a few lines coming from the top of the gas tank, these needed to be disconnected before getting the fuel pump apparatus out.  Disconnecting the lines were the most difficult part of swapping the pump; pliers and a couple screwdrivers were needed to pry the rubber lines from the metal connectors.

Once the lines were off, we unbolted the plate and took out the fuel pump apparatus.

Next, it was time to switch out the actual fuel pump.  Visually, the pumps look exactly the same, the difference is, essentially, that the STi one pumps more fuel into the engine since turbo engines have a higher thirst for fuel.  There is a rubber hose connecting the top of the pump with the assembly that proved to be pretty stuck on.  Unfortunately, we weren’t able to remove the hose without breaking off the top of the fuel pump.

Getting the STi pump in and the assembly back into the tank was much easier than removing it.  And since we couldn’t do much else, that’s all we did that day.

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