Primary engineering on the EJ series was done by Masayuki Kodama, Takemasa Yamada and Shuji Sawafuji of Fuji Heavy Industries,[2] Subaru's parent company.

At the 46th Tokyo Motor Show in October 2019, Subaru announced it would conclude production of the EJ20 by the end of March 2020.

All these engines have the air-to-water intercooler setup (chargecooler) and close deck blocks equipped with piston oil squirters.

This updated type of EJ20G was used in all WRX models since early 1992, cylinder head is equipped with hydraulic lifters compared to the rocker arms used in the previous EJ20G.

These engines can be identified by smooth valve covers, plug leads and a wasted spark coil in the middle of the intake manifold.

To identify an EJ205: Usage: Impreza WRX Forester Cross Sports, S/tb, STI NOTE: The Australian Spec MY00 EJ205 does not have coil on plug but can be identified from the VIN of the vehicle (if known) where the tenth digit will be Y (for year 2000) and the sixth digit will be 8 (for the 2000yr/EJ205) It started its life for the 9/98–8/99 GC8 in Japan, UK, Australia.

To identify a 9/98–9/2000 EJ207 (v5/v6 WRX STI GC8/GF8) V7 are single scroll, AVCS, throttle by cable, top-feed injectors, engines.

The engine speed is limited from the factory at 8000 rpm When compared with the USDM A/C compressor, the JDM Sti is of a different part number and smaller in size.

The Pistons were lighter with a shorter skirt than the WRX EJ20T to allow for higher engine speed.

The hydraulic pressure of the lash adjuster must be overcome during operation and during the most critical time of engine start.

To overcome this situation and to contribute to the total reduction of friction loss, 1997 and later SOHC engines have solid valve adjusters.

Engines with the earlier HLA are recommended to use 10W30 or 10W40 oil year-round; 5W30 can be used at very low winter temperatures.

The carbon composition head gaskets with integrated O-rings are interchangeable from left to right on 1990 to 1994 NA engines only.

Factory boost pressure on the EJ22T is 8.7psi (.59 Bar) Phase two closed deck, based on the North American 1991–94 Legacy Turbo EJ22T engine uses the same casting marks but with a updated thrust bearing to position #5 instead of #3.

It Uses identical cylinder heads and IHI RHF 5HB turbocharger[11] as a EJ20K STi but with a unique closed deck crank case.

That version of the engine used Hydraulic Lash Adjuster (HLA) heads, was recommended to be run on 91 octane fuel, had lower power and torque ratings than the later 1997–1999 EJ25D, and was only offered with an automatic transmission.

In 1997 a revised engine was introduced that used heads with shimmed bucket lifters (rather than the HLAs), was designed to run on 87 octane fuel, and was available with either a manual or automatic transmission.

Because of the DOHC valve architecture, the spark plugs are more difficult to service in comparison to SOHC variations.

[15] Usage: The EJ251 was the first version of the 2.5L single overhead cam (SOHC) engine line by Subaru for the US market.

While Subaru has not provided a direct list of revisions between the EJ251 and less common EJ252, there is some degree of information suggesting the EJ252 was simply an alternate version of the EJ251 made to meet California Emissions Standards when the SOHC EJ engines were first introduced in North America.

Power output has been reported as ISO 115 kW (156 hp) but is often speculated to share the same specs with the largely identical EJ251.

1998–2004 — DOHC with 165 hp (123 kW; 167 PS) at 6000 rpm and 235 N⋅m (173 lb⋅ft) of torque at 2800 rpm Usage: DOHC 16-valve turbo with sodium-filled valves originally designed for North American market, now sees usage in some European Imprezas and Legacy models destined for South Africa and Liberty models for Australia.

It has Dual-AVCS, 9.5:1 CR pistons, E25 heads with provisions for a scavenge oil pump turbo.

2004–2007 STI models used the same shortblock, B25 heads, and valvetrain as the EJ255 in MY 2005–2006 Legacy GT and the same block as the 2004–2005 Forester XT.

Later years used revised block, piston, connecting rods, crankshaft and heads to further improve performance and durability.

MY19 variants of the engine feature a further revised piston design cast from a new alloy for increased strength, further improvements to the general valvetrain, a new ECU and revised engine programming that improved response and widened the torque curve.

Engine has a unique setup, most notable is the oval, single port exhaust, three catalytic converters and five air/fuel and oxygen sensors.

These engines were also all drive by wire (DBW), and had a three piece intake manifold with a tumble valve in the center section.

When those ABS Speed signal are removed, the ECU will force the Engine to run in limp home mode.

[citation needed] The following table has details on a few of the commonly modified Subaru engines: