Subaru EJ208 Engine

Introduction

Subaru’s EJ208 engine was a 2.0-litre horizontally-opposed petrol engine with sequential turbochargers. In Australia, the EJ208 engine was introduced in the 2001 Subaru BE Liberty B4 which, with a manual transmission, produced peak outputs of 190 kW and 320 Nm. From 2002, the BE Liberty B4 was offered with an automatic transmission for which the EJ208 engine was detuned for ‘smooth torque delivery’ and to avoid ‘shift shock’ on gearchanges.

Please note that this article considers the Subaru EJ208 engine as it was available in Australian-delivered vehicles; specifications for other markets may vary.

EJ208 block

The EJ208 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 (the outer surfaces of ‘dry type’ liners are in complete contact with the cylinder walls).

Crankshaft, connecting rods and pistons

For the EJ208 engine, the crankshaft was supported by five bearings that were made from aluminium alloy. For the EJ Phase II engines like the EJ208, the crankshaft thrust bearing was relocated to the rear of the crankshaft (previously the no. 3 bearing).

The EJ208 engine had cast connecting rods and forged aluminium pistons which weighed 162 grams each. For the EJ Phase II engines, friction reduction measures for the pistons included:

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

The piston crowns for the EJ208 engine had flat tops for a compression ratio of 9.0:1.

Cylinder head and valves

The EJ208 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 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.

The EJ208 cylinder head had four valves per cylinder that were actuated by solid valve lifters. The intake valves had hollow stems to reduce mass and inertia, while the exhaust valve stems were filled with sodium. At high temperatures, the sodium would liquefy and its motion within the stem would effectively transfer heat from the valve head to the valve stem, contributing to faster cooling of the valve head. The intake valves weighed 48.4 grams each, while the exhaust valves weighed 46.7 grams each.

Sequential turbochargers

The EJ208 engine had two sequential turbochargers – a primary IHI VF33 turbocharger and a secondary IHI VF32 turbocharger – which operated in three stages:

• Primary stage single turbo operation: at low to medium engine speeds, boost pressure was provided solely by the smaller, ‘primary’ turbocharger. The boost pressure generated by the primary turbocharger was controlled by a wastegate which operated in response to signals from the ECM;
• Intermediate preparatory stage: at medium engine speeds, the exhaust control valve was partially opened – in response to signals from the ECM – so that the secondary turbocharger would begin to rotate. Initially, pressure generated by the secondary turbocharger was redirected to the inlet side of the air intake. Furthermore, the ECM uses a differential pressure sensor to measure the difference in boost pressure between the intake manifold (generated by the primary turbocharger) and the secondary turbocharger; and,
• Secondary stage twin turbo operation: when the ECM determined that engine operating conditions were suitable, the relief valve would close and the exhaust gas control valve would fully open. When the intake control valve was opened, pressure from the secondary turbocharger was supplied to the intercooler. During this stage, boost pressure control was regulated via the primary turbocharger’s wastegate.

In its promotional materials for the Subaru BE Liberty B4, Subaru acknowledged:
‘a slight reduction in the rate of acceleration in the preparatory or intermediate phase that occurs between 4000 to 4500 rpm. During this phase, exhaust pressure previously only supplied to the primary turbocharger is now supplied to both the turbochargers, leading to a temporary and slight reduction in primary boost pressure.’

In testing by Autospeed, however, a ‘significant dip in manifold boost pressure’ of 0.25 to 0.30 bar was observed during the 4000-4500 rpm transition. It is understood that peak boost pressure for the EJ208 engine was 0.933 bar at 4800 rpm.

Intercooler

To reduce the temperature of the intake air after it was compressed by the turbocharger, and increase the density of the intake charge, the EJ208 engine had a Sanden intercooler which had a cooling capacity of 13.37 kW.

Intake

The intake ports for the EJ208 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.

Injection and ignition

The EJ208 engine had computer controlled, multi-point sequential fuel injection system with 550 cc injectors. The injection and firing order for the EJ208 engine was 1-3-2-4.