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The ER series is a flat-6 engine with a displacement of 2.7L manufactured by Subaru, a division of Fuji Heavy Industries. The ER series has aluminium engine blocks and aluminium cylinder heads.
Created as a refined luxury engine with improved power over the EA82T, Subaru introduced the ER series engine in 1988 exclusively to be featured in the Subaru Alcyone VX. Like the EA series engines, the ER series engine featured 2-valve cylinder heads with hydraulic lash adjusters and the block shared the same bore and stroke. While recognised as bearing many similarities to the Subaru EA82 engine, there are numerous differences in design between the two engines and a large portion of parts are unique to the ER27. The oil and water pumps are unique to the ER27, sharing similar bolt patterns and design to the EA82, but being of a higher flow in both cases. The intake manifold uses a two piece design with a lower section bolting to the heads containing the coolant bridge, injectors and various vacuum lines. The upper intake manifold then bolts to the lower section and is unlike the EA82 or EJ22 "spider" manifold designs in that there is no central plenum chamber. The valve timing system is belt-drive using two individual timing belts, curiously one belt uses a spring tensioner (like the EA82) whilst the other uses a hydraulic tensioner (like the EJ22). Both JDM and USDM versions of the ER27 used multi-point electronic fuel injection. The ER27 designation was the first time Subaru incorporated the engine's displacement into the series name and all future engines have retained this nomenclature.