2004 Engine Epic - Subaru Engines

We look at the most desirable modern engines from Subaru...

By Michael Knowling

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One of the biggest recent movers in the high performance scene has been Subaru (aka Fuji Heavy Industries). Since the release of the Liberty (Legacy) RS side-by-side with the SVX, Subaru has continued to build grunty engines with a reputation for reliability.

Modern Subaru engines are identified by a fairly simple four-character code system. The first two characters are letters that indicate the engine family and the second two characters are numbers relating to engine capacity.

Here’s some common Subaru engine codes and what they identify...

Engine Code

Engine Configuration/ Capacity

EJ18

Flat-four/1.8 litre

EJ20

Flat-four/2.0 litre (available in naturally aspirated and turbocharged form)

EG33

Flat-six/3.3 litre

ER27

Flat six/2.7 litre

EN07

In-line four/660cc (available in naturally aspirated and turbocharged form)

Subaru Sixes...

The most potent six-cylinder release from Subaru is the EZ30-R 3.0-litre DOHC, 24-valve flat-six as fitted to the current top-line Japanese Legacy Touring Wagon, B4 and Outback (the latter also available in Australia). This all-alloy motor features AVCS+ continuously variable inlet valve timing (across a 50-degree range) along with variable valve lift. As far as we can determine, variable valve lift in this engine is a first for Subaru. Using a 10.7:1 compression ratio, this sporting engine is rated with a healthy 184kW at 6600 rpm and 304Nm at 4200 rpm. In Australian delivered guise (in the new Outback 3.0R) it delivers 4kW and 7Nm less. A very desirable engine.

Almost as powerful – thanks to a capacity advantage – is the early ‘90s EG33 3.3-litre DOHC, 24-valve flat-six, as fitted to the Subaru SVX coupe. The engine uses a variable induction system, twin knock sensors, 10.0:1 compression and - in Japanese guise - it generates an impressive 179kW at 6000 rpm together with 309Nm at 4800 rpm. Australian delivered examples make 172kW. Like most Subaru engines, the EG33 has many engineering ties to the EJ-series flat-four of the same era.

Next most powerful is the EZ30 3.0-litre, DOHC, 24-valve flat-six as fitted to the mid-range version of the Japanese Legacy. Using the same 10.7:1 compression ratio as the hot EZ30-R engine and with a variable induction system, this motor puts out 162kW at 6000 rpm and 289Nm at 4400 rpm. Australian-delivered EZ30s (non AVCS+) make 154kW and 282Nm at the same revs as the Japanese version.

Reaching back into history, the Japanese model mid ‘80s Subaru Vortex was released with an optional 2.7-litre flat-six. The SOHC fuel injected ER27 was no powerhouse at 112kW, but it was Subaru’s first attempt at a mass produced six-cylinder. Things have improved!

Subaru Fours...

Subaru has earned an enviable go-fast image in the past 10 – 15 years.

The real action started in Japan during 1989, when the local market received the Legacy RS. The RS debuted the now-famous EJ20 2.0-litre turbo engine with DOHC, 16-valve breathing, single turbocharger and an intercooler (which was water-to-air in those early days). Using 8.0:1 compression, the first Japanese-spec Legacy RSs could crank out 147kW at 6000 rpm and 260Nm at 3600 rpm. The same output was claimed by the Australian-delivered Liberty RS of the early ‘90s (essentially a facelift of the original Liberty/Legacy design).

The EJ20 turbo engine has since evolved with various different compression ratios, camshafts, turbocharger sizes, intercoolers and more. There is a bewildering number of variations, but the more common later-model EJ20 turbo engines are rated at 162, 176, 184 and 206kW. These outputs became available in GC-series Impreza WRX sedans and wagons.

Today, the latest Japanese-spec WRX EJ20 turbo engine uses 9.0:1 compression, AVCS variable inlet cam timing and makes 184kW with 333Nm. The current Legacy GT also uses a single (twin scroll) turbo with AVCS and makes up to 206kW and 343Nm at a low 2400 rpm.

In Australia, the ’94 – ‘96 EJ20 turbo engine used a large TD05 turbocharger to make 155kW at 6000 rpm and 270Nm at 4800 rpm. The ‘97/’98 model got a smaller, more responsive turbocharger and a larger intercooler (amongst other things) but output remained at 155kW – though peak power was now at a more accessible 5600 rpm and there was an extra 20Nm 800 rpm lower than before. For the ‘99/’00 power increased to 160kW – with no explanation of how... Power remained at 160kW until the release of the ’03/’04 Australian-spec WRX.

The current model Australian WRX uses a 9.0:1 static compression ratio, AVCS variable valve timing and makes 168kW and 300Nm (at 6000 and 3600 rpm). The local Liberty GT also carries over the EJ20 single turbo design but generates a tidy 180kW at 6400 rpm and 310Nm at just 2400 rpm. At 9.5:1, its static compression ratio is high for a turbocharged engine.

A twin-turbocharged version of the EJ20 - as previously fitted to the Liberty/Legacy B4 – was also introduced in Japan in about 1994. Using a sequentially staged pair of turbochargers and an air-to-air intercooler, these engines started off generating 194kW but soon rose to the regulation 206kW output. Note that output depends on whether the vehicle is fitted with a manual or auto transmission – and whether it is detuned for the Australian market. One thing to plague all EJ20 twin-turbo engines is a mid-range torque hole that occurs as the secondary turbocharger comes into action. Subaru has now dropped the sequential twin-turbo engine...

But the most desirable EJ20 turbo engines are those tweaked by STi. Bigger turbochargers, improved intercoolers with water sprayers, stronger engine internals and a more aggressive overall tune are hallmarks of a STi rework...

Today, the latest Japanese-spec Impreza STi uses 8.0:1 compression, a twin-scroll turbocharger and AVCS variable inlet cam timing to reach 394Nm at 4400 rpm and the regulation 206kW output. Note that the same 206kW output has been achieved by most Impreza STis since late ’96. In comparison, the current Australian-spec STi (with the same mechanicals) is rated at a more modest 195kW and 343Nm.But there’s nothing modest about the Impreza STi that’s currently on offer in North America! The North American STi uses a 2.5-litre capacity (a 25 percent advantage) and thrusts out a substantial 224kW and 408Nm...

Outside of the American Impreza STi, the turbocharged 2.5-litre flat-four – the EJ25-T – can be found in the current Australian Forester XT. Tuned for maximum driveability, this DOHC turbo engine generates 155kW at 5600 rpm and 320Nm at 3600 rpm. In Japan, meanwhile, a Forester STi is available pushing out a massive 195kW – as seen in this graph.

The hottest atmo version of the 2.5-litre flat-four is the Japanese-spec EJ25 DOHC, 16-valver with AVCS that makes 125kW and 238Nm at 6000 and 2800 rpm respectively. Unfortunately, Australia has never received this engine – we get the SOHC version, which currently makes 121kW and 226Nm. Earlier Australian-spec 2.5s made just 119kW and 211Nm.

You might also be interested in another motor not seen in Australia - the highly tuned atmo version of the EJ20. Factory fitted to the current Legacy 2.0R 5-speed manual, this engine employs a high 11.5:1 compression ratio and DOHC, 16-valve heads with AVCS. Output is an impressive 140kW at 7100 rpm (!) with 196Nm at 4400 rpm.

On the smaller side of things, the Subaru EN07 engine flies the flag. Displacing just 660cc, the EN07 is available in various different guises but the hottest is fitted to the Japanese Pleo and R2-S Kei-classer. With DOHC, 16-valve breathing, a 9.0:1 static compression ratio and the aid of a supercharger and intercooler, this in-line four-banger slogs out 47kW at 6000 rpm. Peak torque is 103Nm at 3200 rpm. A naturally aspirated DOHC version with AVCS is also available – this makes 40kW at 6400 rpm.

For those with a good memory, Subaru also dabbled with turbocharging in the early/mid ‘80s with their EA-series flat-four. The ‘ultimate’ OHC version of the EA82 1.8-litre turbo came non-intercooled and producing up to a meagre 101kW at 5600 rpm. While it's no powerhouse, these engines are tough-as-nails – something Subaru has built its reputation on.

Subaru Performance Motors at a Glance...

Sixes
EZ30-R 3.0 litre flat-six DOHC (AVCS+)
184/180kW

EG33 3.3 litre flat-six DOHC

179/172kW

EZ30 3.0 litre flat-six DOHC

162/154kW

ER27 2.7 litre flat-six SOHC

112kW

Fours
EJ25 2.5 litre DOHC Turbo (US STi)

224kW

EJ20 2.0 litre DOHC Turbo

147 - 206kW

EJ20 2.0 litre DOHC Twin Turbo

194 - 206kW

EJ25 2.5 litre DOHC Turbo (Forester STi)

195kW

EJ25 2.5 litre DOHC Turbo

155kW

EJ20 2.0 litre DOHC (11.5:1 CR)

140kW

EJ25 2.5 litre DOHC

125kW

EJ25 2.5 litre SOHC

121/119kW

EA82 1.8 litre SOHC Turbo

101kW

EN07 660cc DOHC Supercharged

47kW

EN07 660cc DOHC AVCS

40kW

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