Subaru EN engine

The EN series engine is used for kei cars sold by Subaru in Japan. It is a four-cylinder, four-cycle engine introduced in 1989 and discontinued in 2012. It was a replacement for the two-cylinder EK23 that was used in the Subaru Rex. While other manufacturers adopted a three-cylinder engine, the Subaru EN is a four-cylinder of only 547 cc. Subaru also did make a three-cylinder engine, called the Subaru EF engine which was used in the Subaru Justy, but the larger EF engine (which was based on the smaller EK23) was not modernized at the same time.

The following year, 1989, the Japanese Ministry of Transport revised the standards for kei cars. This resulted in the new 660 cc class series of four-cylinder engines, and the EN05 had its stroke increased to produce the EN07. The bore pitch remained 62.5 mm (2.46 in) as the changes were kept to a minimum. The increased stroke helped make up for the lack of low-speed torque, a weakness of the other four-cylinder 660 cc engines. While four-cylinder engines are not typical in kei class cars, Subaru still primarily uses this layout. Three-cylinder engines have proved to be on par with Subaru's four-cylinder designs; while not as smooth running they tend to be lighter and more economical due to lower friction losses. Nonetheless, the EN07 powered three of the five most fuel efficient kei passenger cars in 2009 (heading the list for the third year in a row), when the EN engine was its peak of development.

There was a turbocharged version of the predecessor, the EK23, used in the Subaru Rex, which competed with the Daihatsu Mira and Suzuki Alto. This was replaced with a supercharger for the EN-series. The four-cylinder EN engine was originally marketed as the Clover4, and Subaru engraved the head with a clover-leaf mark, to set it apart from its three-cylinder version. Subaru remained faithful to the EN-series until they stopped building kei car engines. Subaru uses Daihatsu three-cylinder units for the Sambar truck (now a rebadged Daihatsu Hijet) since 28 February 2012.

The EN05 was the first engine in the EN series. Variants include a naturally aspirated model with a carburetor, and the EMPi equipped with a supercharger. Cylinder dimensions are slightly oversquare.

The EN05 had its stroke lengthened to reach the new 660 cc limit set for kei cars by the Japanese government for March 1990, making it a decidedly long-stroked unit.

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Wikipedia