Block and crankcase
The Subaru EJ20X and EJ20Y engines had an aluminium alloy block with 92.0 mm bores – with cast iron cylinder liners – and a 75.0 mm stroke for a capacity of 1994 cc. The cylinder block for the EJ20X and EJ20Y engines had an open-deck design whereby the cylinder walls were supported at the three and nine o’clock positions.
The crankcase for the EJ20X and EJ20Y engines had five main bearings and the flywheel housing was cast with the crankcase for increased rigidity. The EJ20X engine is understood to have a forged crankshaft and connecting rods, but cast aluminium pistons with forged crowns.
Cylinder head and dual AVCS
The EJ20X and EJ20Y engines had an aluminium alloy cylinder head with cross-flow cooling, double overhead camshafts (DOHC) per cylinder bank and four valves per cylinder that were actuated by roller rocker arms.
The EJ20X and EJ20Y engines were the first EJ engines to be equipped with Subaru’s ‘Dual Active Valve Control System’ (‘Dual AVCS’) which provided variable intake and exhaust valve timing.
Turbochargers and intercooler
For the BL.I Liberty GT, the EJ20X engine was fitted with a twin-scroll IHI VF38 turbocharger; the EJ20Y engine, however, had a larger twin-scroll Mitsubishi TD04 HLA 19T turbocharger. For the BL.II Legacy GT (i.e. MY07), both the EJ20X and EJ20Y had an IHI VF45 turbocharger, though these EJ20X/EJ20Y engines were not offered in Australia (hence the reference to Legacy rather than Liberty).
In a twin-scroll turbocharger, the exhaust manifold separates the channels for cylinders that can interfere with each other, so that the pulsating exhaust gases flow through separate spirals (or scrolls). As a result, the low pressure tail component of an exhaust pulse can be used to: 1) extract all the combustion products from the cylinder head; and, 2) induct the intake charge during periods when both intake and exhaust valves are partially open.
After the turbocharger, the compressed air was passed through a low-restriction, transversal flow intercooler to reduce its temperature and thereby increase its density for the intake charge. For mass reduction, the intercooler had a lightweight resin tank.
Injection and ignition
The EJ20X and EJ20Y engines had multi-point sequential fuel injection and centrally located spark plugs. Furthermore, the EJ20X and EJ20Y engines had two ignition coils (one for each pair of cylinders, i.e. 1-2 and 3-4) which fired the spark plugs directly twice per cycle.
For the EJ20X and EJ20Y engines, the injection and firing order was 1-3-2-4; its compression ratio was 9.5:1