The Subaru six-cylinder engines are a series of flat-6 engines manufactured by Subaru, made in three distinct generations. The ER27, derived from the Subaru EA first-generation flat-4, was used as the sole engine option in the premium model 1988–91 Subaru Alcyone VX (XT6 in the United States). The EG33, derived from the Subaru EJ second-generation flat-4, was used exclusively in the successor Subaru Alcyone SVX, again as its sole engine option, sold from 1991–96. The EZ series, consisting of the EZ30 and EZ36 models, was designed to be almost as compact as the EJ25 flat-4. The EZ30/36 were the first Subaru six-cylinder engines available outside the sport coupes, used as the uplevel option for Subaru Legacy (2002–19) and Outback/Lancaster (2001–19) as well as the sole option in the Subaru Tribeca (2006–14).

Created as a refined luxury engine with improved power over the EA82T, Subaru introduced the ER27 engine in November 1985 for the Subaru ACX-II concept car, shown at the Tokyo Motor Show and billed as the 'concept car of the near future.'^[2] The concept went into production as the Subaru Alcyone VX (Subaru XT6 in North America) in August 1987,^[3] the exclusive application for the ER27.

When the ER27 was introduced, it was the only water-cooled flat-6 automobile engine on the market.^[4] The ER27 designation was the first time Subaru incorporated the engine's displacement into the engine designation and all subsequent engine codes have retained this nomenclature.

Similar to how the six-cylinder ER27 is related to the earlier four-cylinder EA82, the EG33 shared bore and stroke dimensions with the contemporary four-cylinder EJ22.^[1] The EG33 was exclusively fitted to the Alcyone SVX, where it was paired with the 4EAT automatic transmission in both front- and all-wheel-drive configurations.^[13]

After the SVX was discontinued, Subaru did not offer a six-cylinder engine until the EZ30 was developed and released for the Subaru Outback.

In the United States, the EZ30 was introduced in the Outback H6-3.0 in November 2000 for the 2001 model year.^[25][26] In Japan, the EZ30 was introduced in the equivalent Lancaster 6 wagon in May 2000.^[27] A twin-turbo version of the EZ30 was produced for the Subaru B11S concept car, unveiled at Geneva in 2003.^[28] The EZ30 was refreshed in 2003, and when the Tribeca was introduced for the 2006 model year in January 2005, the EZ30 II was the sole engine option.^[29]

The EZ36 was introduced with the restyled Tribeca for the 2008 model year,^[30] and replaced the 3.0 L EZ30 in the Legacy and Outback starting in 2009 for the 2010 model year.^[31][32]

Starting with the 2020 model year, the six-cylinder EZ36 was dropped as the uplevel engine option for Subaru Legacy and Outback automobiles and instead the premium engine offered was the turbocharged four-cylinder FA24F, which was previously introduced for the 2019 model year as the sole engine option for the Subaru Ascent, the successor to the Tribeca.

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