EJ204 block and crankcase
Like the EJ202, 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 GD/GG Impreza 2.0R and BL/BP Liberty 2.0R had a compression ratio of 10.0:1, the EJ204 engine for the GE/GH Impreza had a compression ratio of 10.2:1.