The EN series engine is a four-cylinder, four-stroke engine used in kei cars sold by Subaru in Japan, succeeding the EK family of two-cylinder engines previously used in Subaru kei cars from 1958 to 1989. The EN family was introduced in 1989 (as the EN05) and discontinued in 2012.
Overview
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 to help keep the changes 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 kept using this layout until they stopped manufacturing their own kei vehicles in 2012. 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 Clover 4, and Subaru cast 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.
EN05
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.
Common to all EN05 variants: SOHC 8-valve Displacement: Bore × stroke:
EN05A (naturally aspirated carburetor) Compression ratio: 10.0 Output: at 7500 rpm, at 4500 rpm (KH2 1986 Subaru Rex)
EN05Z (supercharged) Compression ratio: 8.5 Output: at 6400 rpm, at 4400 rpm (KH2 1986 Subaru Rex)
EN07
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.
Common to all EN07 variants: Displacement: Bore × stroke:
EN07A (Naturally Aspirated carburetor) Installed in the Vivio Van.
SOHC 8-valve
Compression ratio: 10.0
Specification Reference: at 7000 rpm, at 4500 rpm (KW series Subaru Vivio)
EN07C (Naturally Aspirated carburetor) The engine was installed in the early Sambar van and truck. Compression ratio dropped slightly, and tuning emphasized low-rpm torque.
SOHC 8-valve
Compression ratio: 9.8
Specification Reference: at 6500 rpm, at 3500 rpm (KV3 series Sambar)
EN07L (LPG carburetor version) SOHC 8-valve Compression ratio: 9.8
Used in: Subaru Sambar Subaru Sambar Dias
EN07E (Naturally Aspirated EMPi) The EN07A engine (with a carburetor) became EN07E with EMPi.
SOHC 8-valve
Compression ratio: 10.0
Specification Reference: at 7200 rpm, at 5600 rpm (KK3 VIVIO MT version)
Used in: Subaru Rex Subaru Vivio Subaru Pleo
EN07F (Naturally Aspirated EMPi) The EN07C engine (with a carburetor) became EN07F with EMPi. The rocker cover on the delivery service version had a crimson ceramic coating.
SOHC 8-valve
Compression ratio: 9.8
Specification Reference: at 6400 rpm, at 3200 rpm (TV1 series Sambar)
EN07S (Naturally Aspirated SPI) Was installed in the Pleo Van EGI SPI (single point injection) engine design.
SOHC 8-valve
Compression ratio: 10.0
Specification Reference: at 6400 rpm, at 4000 rpm
Used in: Subaru Pleo
EN07V (Naturally Aspirated SPI) The EN07F with EMPi became an EN07V with SPI. The rocker cover on the delivery service version also had a crimson ceramic coating.