Subaru EJ205 Engine

Introduction

Subaru’s EJ205 was a 2.0-litre horizontally-opposed (or ‘boxer’) four-cylinder turbocharged petrol engine. In Australia, the EJ205 was available in the SF.II Forester GT from August 1998 and the GC.II/GM.II Impreza WRX from September 1998. As member of the Subaru’s EJ Phase II engine family, the EJ205 engine had a newly designed cylinder head with ‘tumble swirl’ intake ports, while the crankshaft thrust bearing was relocated to the rear of the crankshaft.

Key features of the EJ205 engine included its:

• Die-cast aluminium, open-deck block;
• Die-cast aluminium cylinder head;
• Belt-driven double overhead camshafts; and,
• Four valves per cylinder.

Please note that this article the EJ205 engine as it was supplied in Australian-delivered models; specifications for other markets may vary.

EJ205 block

The EJ205 engine had a die-cast aluminium alloy cylinder block with 92.0 mm bores and a 75.0 mm stroke for a capacity of 1994 cc. The cylinder block had an open-deck design to enhance cooling efficiency and dry-type, cast iron cylinder liners.

Crankshaft, connecting rods and pistons

For the EJ205 engine, the crankshaft was supported by five bearings that were made from aluminium alloy. For the EJ Phase II engines, the crankshaft thrust bearing was relocated to the rear of the crankshaft (previously the no. 3 bearing).

The EJ205 engine had cast pistons and connecting rods. For the EJ Phase II engines, lighter and lower-friction pistons were introduced with the following properties:

• Reduced piston pin offset;
• Solid type piston skirts;
• Molybdenum coating; and,
• Reduced top land to cylinder clearance.

The EJ205 engine did not have oil jets in the cylinder walls for lubrication, instead relying on oil splash.

Cylinder head

The EJ205 engine had a die-cast aluminium cylinder head with double overhead camshafts (DOHC) per cylinder bank. A single timing belt was used to drive the four camshafts – it consisted of a strong and inflexible core wire, wear-resistant canvas and heat-resistant rubber material. For quiet operation, the teeth on the timing belt had a round profile. The EJ205 cylinder head had four valves per cylinder that were actuated by solid valve lifters.

The recommended replacement interval for the cam belt was 100,000 kms or four years, whichever occurred first. A self-adjusting, hydraulic tensioner maintained timing belt tension and valve clearance checking/adjustment was only necessary every 150,000 kms.

AVCS: GD.II/GG.II Impreza WRX

For the GD.II/GG.II Impreza WRX, the EJ205 engine had Subaru’s ‘Active Valve Control System’ (AVCS) which adjusted the opening and closing timing of the intake valves by changing the phase angle of the camshaft sprocket relative to the camshaft; for the GD.II/GG.II Impreza WRX, it is understood that the maximum range of adjustment was 35 crankshaft degrees. Under the control of the ECM, an oil flow control valve would move its spool to switch the hydraulic passage to/from the advance and retard chambers in the camshaft sprocket to vary the phase angle between the camshaft sprocket and camshaft.

Based on input signals from the air flow sensor, engine coolant temperature sensor, throttle position sensor and camshaft position sensors, the engine control unit could use three computer maps to achieve the following –

• Optimum valve timing for stable idling: minimal intake and exhaust valve overlap);
• Improved fuel consumption at medium engine speeds and low loads: intake valve timing was advanced to reduce intake air blow back and improve fuel consumption. Furthermore, increasing intake and exhaust valve overlap enhanced exhaust gas recirculation (EGR) for a reduction in NOx emissions. When engine load increased, advancing the intake closing time utilised the inertia of the intake air to create a supercharging effect; and,
• Maximum power at high engine speed and load: intake valve timing was further advanced to maximise overlap and utilise the scavenging effect produced by exhaust gas pulsations to draw intake air into the cylinder. Since the intake valve was closed at the end of the intake stroke, air intake efficiency was improved and power increased.

Intake

The intake ports for the EJ205 engine were designed to create a ‘tumble swirl’ air motion as the air and fuel entered the cylinder – this action improved mixing of the air and fuel for more uniform flame travel and faster combustion. According to Subaru, the tumble swirl intake ports enabled maximum gas pressure (downward force) to be applied to the piston 10-15 degrees ATDC when the maximum turning moment on the crankshaft occurred, resulting in a greater power output.

For the GD/GG Impreza WRX (October 2000) and the SF.II Forester GT (December 2000), Tumble Generator Valves (TGV) was introduced for lower exhaust gas emissions at low speed cold engine conditions. Specifically, the TGV worked by closing a butterfly valve in the intake manifold to create a tumble air motion at low intake air speeds, thereby improving air/fuel mixing for improved combustion efficiency and emissions.

Impreza WRX: TD04 and TD04L turbochargers

Like the EK20K engine, the EJ205 engine for the Subaru GC/GM Impreza WRX was fitted with a Mitsubishi TD04 turbocharger.

For the Subaru GD/GG Impreza WRX, the EJ205 engine had a Mitsubishi TD04L turbocharger. Compared to the TD04 unit in the GC/GM Impreza WRX engine, the TD04L turbocharger had an approximately 10 per cent larger turbine. According to Subaru, the TD04L turbocharger:

• Had an A/R ratio of 13.0:1 for quick turbo response at low rpm;
• Provided maximum sustained boost pressure of 700 mm Hg (i.e. 0.933 bar or 13.5 psi) at 4800 rpm at full load); and,
• Had a maximum turbine speed of 190,000 rpm.

Forester GT: Mitsubishi TD035 turbocharger

In contrast to the Impreza WRX, the Subaru SF Forester GT had a smaller, Mitsubishi TD035 turbocharger which provided lower boost pressure and had a greater emphasis on mid-range (rather than top-end) performance.

Intercooler

For both the Impreza WRX and Forester GT, the EJ205 engine had an air-cooled intercooler that was mounted on top of the engine. Since the turbocharging process increased the temperature of the intake air, it was then passed through an air-cooled intercooler that received air via the bonnet duct; the intercooler reduced the temperature of the intake air to increase its density for greater power.

For the EJ205 engine in the Subaru GC/GM Impreza WRX, the intercooler had a cooling capacity of 6.9 kW (refrigeration kilowatt). For the Subaru GD/GG Impreza WRX, however,

• The intercooler was 12 per cent larger;
• The angle of the intercooler relative to the bonnet was revised;
• The bonnet duct was reshaped to increase airflow through the intercooler; and,
• Cooling capacity was 13.2 kW.

Injection and ignition

The EJ205 engine had computer controlled, multi-point sequential fuel injection system with full direct ignition control. The ignition coil was positioned in the cylinder head, directly above the platinum tipped spark plug which had replacement intervals of 100,000 kilometres. The injection and firing order for the EJ205 engine was 1-3-2-4.

The knock control system for the EJ205 engine had ‘fuzzy logic’ which enabled the maximum ignition advance angle to be used without detonation since the ignition program continually adapted to changes in environmental conditions and fuel quality. The EJ205 engine required 95 RON premium unleaded petrol or higher.

Compression ratios for the EJ205 engine were as follows:

• Subaru SF Forester GT: 8.5:1;
• Subaru GC.II and GM.II Impreza WRX: 8.0:1;
• Subaru GD.I and GG.I Impreza WRX: 8.0:1; and,
• Subaru GD.II and GG.II Impreza WRX (from November 2002): 9.0:1.

December 2000: Forester GT changes

In December 2000, a range of changes for the Forester GT’s EJ205 engine were introduced:

• To comply with Euro STEP3 emissions standards, a pre-catalytic converter was fitted between the exhaust port and the turbocharger;
• Equal length intake manifolds were introduced for more progressive on-boost performance
  The intake ports were revised for greater efficiency;
• As detailed above, a Tumble Generator Valve (TGV) was introduced in the intake manifold to create tumble air motion for better air/fuel mixing and lower emissions on cold starts. At higher loads or when engine temperatures exceeded 63 degrees Celsius, the valve would open for greater air flow;
• The TD035 turbocharger had an increased diameter turbine housing inlet for improved exhaust glow;
• A four coil, direct ignition system was introduced; and,
• Engine diagnostics were upgraded to meet the European E-OBD standard.

October 2000: GD/GG Impreza WRX changes

With the release of the Subaru GD/GG Impreza WRX in October 2000, the following changes were introduced for the EJ205 engine:

• The TD04L turbocharger replaced the GC/GM Impreza WRX’s TD04 turbocharger;
• A 12 per cent larger intercooler which was repositioned relative to the bonnet and had a re-shaped bonnet duct for greater air cooling. As a result of these changes, the cooling capacity of the intercooler increased from 6.9 kW (for the GC/GM Impreza WRX) to 13.2 kW;
• A new intake manifold with a Tumble Generator Valve (TGV) which created a tumble air motion for better air/fuel mixing and lower emissions on cold starts;
• The combustion chambers were revised;
• A four coil, direct ignition system was introduced; and,
• A pre-catalytic converter was fitted between the exhaust port and the turbocharger.

November 2002: GD.II/GG.II Impreza WRX changes

With the release of the GD.II/GG.II Impreza WRX in November 2002, the following changes were introduced for the EJ205 engine:

• Subaru’s ‘Active Valve Control System’ provided variable intake valve timing;
• The compression ratio was increased from 8.0:1 to 9.0:1;
• The bonnet scoop/duct was redesigned for better airflow; and,
• The pre-catalytic converter that was introduced in October 2000 was discontinued.