The Subaru EJ204 was a 2.0-litre horizontally-opposed (or 'boxer')
four-cylinder petrol engine with double overhead camshafts.
aspirated E204 engine was initially introduced in the 2005 Subaru GD/GG Impreza
and 2006 Subaru BL/BP Liberty
as a more powerful alternative to the
single overhead cam
, but effectively replaced the EJ202 when
the GE/GH Impreza was released in 2007. The EJ204 engine was also fitted
with Subaru’s ‘Active Valve Control System’ (AVCS) which provided variable
intake valve timing.
EJ204 block and crankcase
, the Subaru EJ204 engine had an aluminium alloy block with 92.0 mm
bores – with cast iron dry-type cylinder liners – and a 75.0 mm stroke for a
capacity of 1994 cc. The cylinder block for the EJ204 engine had an
open-deck design whereby the cylinder walls were supported at the three and
nine o’clock positions.
The crankcase for the EJ204 engine had five
main bearings and the flywheel housing was cast with the crankcase for
increased rigidity. Like the EJ202 engine, the crankshaft thrust bearing was
positioned at the rear of the crankshaft.
Cylinder head and camshafts
The EJ204 engine had an aluminium alloy cylinder head with cross-flow
cooling. It is understood that the intake ports for the EJ204 engine created
a ‘tumble swirl’ motion for air as it entered the cylinder for better mixing
of the air and fuel for more uniform flame travel and faster combustion.
The EJ204 engine had belt-driven double overhead camshafts (DOHC) per
cylinder bank which actuated four valves per cylinder by roller rocker arms.
Furthermore, the EJ204 was fitted with Subaru’s ‘Active Valve Control
System’ (AVCS) which could rotate the intake camshaft relative to the
camshaft sprocket within a maximum range of 50 crankshaft degrees to provide
variable intake valve timing.
Injection and ignition
The EJ204 engine had multi-point sequential injection and centrally located
spark plugs. The injection and firing order was 1-3-2-4. The EJ204 engine
had an ignition coil for each cylinder that was positioned directly above
the platinum-tipped spark plug; the replacement interval for the spark plugs
was 112,500 kilometres. The EJ204 engine had an ignition knock control
facility with fuzzy logic that enabled the maximum ignition advance to be
used without detonation by constantly adapting to changes in environmental
conditions and fuel quality.
It is understood that the EJ204 engine
had cast aluminium pistons with a molybdenum coating, solid-type piston
skirts and a flat top combustion surface. While the EJ204 engine for the
BL/BP Liberty 2.0R
had a compression ratio of 10.0:1, the EJ204 engine
had a compression ratio of 10.2:1.