Subaru EK20 Hybrid How-To - Engine Swap

Hybrid No. 14: Almost Any Subaru Chassis, GDB WRX Engine

What And Why
Why? Maybe you wanted a WRX back when they weren't available here, and now that they are, you can't muster the same excitement. Maybe it's the styling, the dynamics (most agree the old car offered livelier handling), weight, cost, or some neurotic desire to own a fast Forester or Legacy. Don't be ashamed, you aren't alone.

Well, unless you're the Forester guy.

Besides these obvious benefits, the older, naturally aspirated cars also offer shorter gearing, turning the turbocharged EJ20's boost into thrust far more effectively than the long-legged WRX gearbox does.

Picking The Chassis
The Impreza body goes all the way back to 1993, so the options are nearly endless. Here are some guidelines, though.

Start with an all-wheel-drive car. Unless it's free, the cost and effort to convert a front-drive car to all-wheel drive won't be worth it. Unless, that is, you want a front-drive WRX. In that case, knock yourself out.

Cars from 1996 and later are easier (and all of them are AWD) because they share the basic OBDII wiring architecture with the WRX. This swap is possible with earlier cars, but more splicing and connector swapping is necessary.

Most of this Hybrid How To is actually based on a WRX-powered Legacy swap performed by i-Speed USA. These guys do WRX swaps all day long, and they say the procedure is effectively the same for a Legacy as it is for Imprezas or Foresters.

Picking The Engine
If you want your car to be legal in California, you'll need to get a U.S. engine from a car that's the same year or newer than yours. You also might want to shy away from engines newer than 2002 as we've noticed they tend to make a little less power (about 10 hp) than earlier engines.

If California legality isn't an issue, you can also consider a Japanese engine. There have been countless versions of the WRX engine in Japan. If you choose to go this route, though, you can only use this Hybrid How To as a rough guide. Early GC8 chassis (1993 to 2001) Japanese engines had a completely different wiring harness and engine management system than the U.S. cars. The GDB (2002 to current) engines have the same basic architecture, but are missing the evaporative emissions controls and have extra wires for the AVCS variable valve timing.

With either U.S. or Japanese engines, be absolutely sure you get a complete wiring harness and ECU with your engine. For U.S.-spec GDB WRX engines, you'll need the entire vehicle wiring harness, not just the underhood part. For earlier Japanese GC8 engines, you can just get the engine harness.

On its way to the turbo, A WRX's exhaust squeezes between the crossmember and the passenger's side cylinder head. You will need a crossmember from a WRX or 1990-to-1994 Legacy Turbo to provide clearance.

Picking The Transmission
Aside from the gear ratios, we couldn't find any definitive info about differences between the WRX and lesser Subarus. They all look the same, and the iSpeed boys know only that it seems to take about the same amount of time to break a regular Impreza transmission as it does to break a WRX tranny. As with any transmission, durability depends on how you treat it. i-Speed's Adam Levy, whose brain was the source for most of this information, has been running a 2.5 RS transmission behind his 260-whp WRX engine for 30,000 miles without problems. He knows others, however, who with only slightly more power, go through a transmission every other month. Your mileage may vary.

If you can treat the gearbox with respect, you want anything but a WRX transmission. WRX gears are way too tall, and the ratios in the naturally aspirated cars are much shorter. If you do switch to a WRX box, be sure to switch to a WRX differential as well, otherwise the front and rear wheels will go different speeds and you'll break the gearbox before you get out of the driveway.

The other option, of course, is an STi six speed. If you do this, remember that you'll need an STi diff, all four axles, and all four hubs. Everything STi is substantially beefier.

Whichever you choose, be sure to use a clutch designed for your transmission. Naturally aspirated cars use a push-style clutch, while WRXs use a pull-style; the two are not interchangeable. You'll need a stronger aftermarket clutch, of course, if you use the naturally aspirated transmission.

Engine Removal And Prep Work
Removing the engine is fairly simple and is best done through the top with a hoist. If you're using the stock transmission, you can leave it in the car. i-Speed does this with a simple transmission support built from a 4x4 piece of lumber, a few angle brackets and an eyebolt. The beam rests on the inner edges of the front fenders and supports the transmission via the pitching rod bracket on the top of the bell housing.

The radiator should also be removed, as the engine must move forward to disengage the clutch from the transmission input shaft before being removed.

Once the engine is out, the crossmember will have to be removed. To do so, you'll first need to unbolt the control arms and steering rack from the crossmember and unbolt the steering shaft from the steering rack. The rack can then drop down and hang from the steering arms.

Mounting The Engine
Installation of the new crossmember is the opposite of removal, with one critical exception. The newer generation GDB chassis has a wider bushing on the front lower control arm, and the control arm slot on the crossmember is correspondingly wider. You must use a carefully selected stack of washers to fill the gap. Just a hint, though. Call them a shim stack, not a washer stack. It makes you sound smarter.

Exhaust
A downpipe and cat for a WRX should fit in any Subaru the engine fits. If you're swapping into an Impreza, in fact, the entire WRX exhaust will fit, with the exception of the front muffler hanger, which you can just leave off. A Forester or Legacy will require a custom or modified Impreza exhaust after the cat.

Cooling System
WRX radiator hoses almost fit. In fact, in most cases, the lower hose can be installed with only minor trimming. The same is true of the upper hose on '99-and-newer cars, while the earlier cars require you to make a new upper radiator hose out of two 90-degree bends and a few inches of pipe.

The WRX's pressure cap is on the engine, so the pressure cap on the radiator needs to be modified to allow coolant to flow from the old cap to the engine-mounted tank. Remember, this hose will be pressurized, so use a reinforced, high-pressure hose.

Miscellaneous
On the off chance your car doesn't have a hood scoop, you better get one. If you already have a hood scoop, you'll need the proper diverter and seal that mate the scoop to the intercooler. The intercooler won't do much good if the air can just blow around it. A WRX diverter will work with some minor trimming and drilling, or you can try to find one for a Japanese hood.

Cars that are '99 and newer have a shorter throttle cable, but creative use of the cruise control cable bracket can make it work-assuming, of course, that you don't want cruise control.

One last detail: You'll also have to find a place to mount the WRX power-steering reservoir.

The Wiring Job
This is a big job. There isn't all that much cutting and splicing, but there is a lot of identifying, unwrapping, and relocating of wires and connectors. We'll cover the basics of what you have to do, but details like wire color or connector shapes may change from year to year. The only way to be sure of what you're doing is to invest in two wiring diagrams, one for the car your donor engine and harness came from, and another for your car.

Prepping The WRX Harness
The WRX doesn't have separate engine and chassis wiring harnesses like most cars. The two are integral, with the critical engine-related portions entering the engine compartment in three different places. To do this swap properly, i-Speed starts with a complete WRX harness, from the engine all the way back to the fuel pump.

If you can, buy a harness that's already out of the car. If you have to remove it yourself, the main branch of the harness is under the dash along the firewall. Pull the dash, the dash bar, the heater core, and then pull the extremities of the harness in toward this section. If nothing else, it'll be good practice for when you do the same thing to integrate the WRX harness into your car.

First, you should identify and label every engine-related part of both the WRX harness and the one in your car. On the WRX harness, there are two firewall grommets. The passenger's-side grommet contains wires for the MAF, boost control solenoid, EGT probe, front O2 sensor, and passenger's-side tumble generator valves. Keeping the engine compartment portion intact, you should be able to strip this portion of the harness down until it's one clean bundle from those connectors to the ECU.

The grommet behind the intercooler has the wires for the rear O2 sensor, gear position sensors, and speed sensors. You'll want to keep the O2 sensor plug, but the plugs on the transmission tend to be different between the WRX and the earlier cars, so it's simpler to cut these wires and splice the new engine harness to the car's transmission harness.

A third branch of the harness runs down the left front fender and terminates in two large connectors, one brown and one black. For simplicity, we've dubbed this branch of the harness the Very Important Branch (VIB), and the brown and black connectors the Very Important Connectors (VICs). The VICs house wires for the oil pressure switch, power-steering oil pressure sensor, driver's-side tumble generator valves, idle air-control valve, coolant temp sensors, Throttle Position Sensor, Manifold Air Pressure sensor, the ignition coils, engine ground, purge control solenoid, and fuel injectors. This VIB also carries power from the main power relay. All of the VIB, except the main power wires, go to the Super Multiple Junction or SMJ, (Subaru's phrase, not ours) a large connector under the left side of the dash that allows the VIB to be separated from the rest of the harness fairly easily.

There should be a fourth branch of the harness going back to the fuel pump and evaporative controls. You'll need this whole branch, the WRX fuel pump, and the fuel pump controller. The controller varies the fuel pump voltage, giving more pressure when the ECU asks for it. Naturally aspirated Subarus run the same fuel pump voltage all the time.

With these four branches isolated, there should still be several wires scattered throughout the harness that you need to identify and free from the harness. Double check with that wiring diagram you got, but you should be looking for wires for the defroster, illumination, OBDII connector, the ECU reflash plug, and the check connector used for Subaru's diagnostic tool. For many of these, it's easiest to cut the wire and splice it to the existing wire in the new car.

Installing The Harness In The New Car
Most of the work happens inside the car, so remove the dash, dash bar and heater core. Now that you're good and pissed off, take a break before tackling the wires.

There are two basic branches of the ECU harness; one goes to the engine compartment and the other scatters throughout the chassis. First, you'll want to pull the engine compartment wires into the interior, identify them, and determine which need to be replaced with wires from the new engine harness.

Next, mount the new ECU and connect the new ECU connector to it. You can feed the engine compartment wires through the firewall one at a time, routing them neatly to their final destinations. As you do this, keep them bundled neatly; you'll eventually wrap these and they'll become your new harness.

Finally, one by one, you'll need to identify all the chassis wires and splice them to the chassis harness. As you do this, you'll be trimming these wires from the car's original ECU harness. After somewhere between 30 and 50 splices, you'll find the only thing left connected to the old ECU connector are the engine compartment connectors you already replaced.

You did it. You should test start the car before wrapping up the harness and re-installing the interior. By now you'll be dying to crank up the boost and go break off some Camaros, but have patience. Be sure to bolt the steering shaft back in properly and have some wrench-savvy friends check over your hack job before you crank the boost. And one last thing: Shift gently.

Swap Basics
*Chassis: First-Generation (GC8) Subaru Impreza, Outback Sport, or Forester, or 1995 or newer LegacyThough not as rigid as the current model, the first Impreza was significantly lighter. Depending on trim, the difference can be as much as 400 pounds. Other than that, the two cars are substantially the same, with virtually the same suspension, brake and steering systems. The Outback Sport is just an Impreza with two-tone paint; the Forester an Impreza with a taller, boxier body on it; and the Legacy basically an XL Impreza. Mechanically, they're all brothers.

*Engine: EK20, Pulling the engine from a U.S.-spec WRX and doing the conversion thoroughly will allow you to register the car legally, even under the strict eye of the California smog man. If that's not an issue, pulling the engine from a Japanese model can get you substantially more power, but be warned; the wiring can be very different on Japanese cars.

*Concerns: Mechanically, this is as simple as swaps get. Electrically, though, it's a mess. You don't have to do anything fancy to put a WRX wiring harness in your Impreza, but you do have to fearlessly disassemble both your harness and the donor harness. Be sure you can read a wiring diagram.

Subaru Gearboxes
  2000-2001 FORESTER/IMPREZA 2000-2003 LEGACY/GT/OUTBACK,
2002-2003 FORESTER/IMPREZA
2002-2004 WRX STI 6-SPEED
1 3.545.:1
3.454:1
3.454:1
3.636:1
2 2.111:1
2.062:1
1.947:1
2.375:1
3 1.448:1
1.448:1
1.366:1
1.761:1
4 1.080:1
1.088:1
0.972:1
1.346:1
5 0.780:1
0.780:1 (Outback=0.871:1) 0.738:1 0.971:1
6 na
na
na
0.756;1
Final 4.111:1 4.111:1 (front)3.900:1
(internal reduction) 1.100:1
(rear final) 3.545:1
3.900:1
SOURCEBOX
i-Speed USA
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