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The Subaru EJ20 Turbo Guide

The detailed evolution of the Subaru EJ20 turbo engine

By Michael Knowling

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At a glance...

  • Guide to Subaru EJ20 turbo engines
  • Mechanical specs
  • Power and torque figures
  • Driveline configurations
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In previous decades there was no such thing as a high performance Subaru engine. That is, until the quad-cam EJ20 turbo debuted in Japan during 1989. The EJ20 turbo engine has since had a massive impact on performance scene around the world; it’s seen many years of rally competition and is one of the most commonly modified engines in existence.

But not all EJ20s are created equal. In this article we’ll look at the evolution of the groundbreaking EJ20 turbo...

The First Generation EJ20 Turbo

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First appearing in the Japanese market BC/BF-series Legacy RS/GT of 1989, the EJ20 turbo engine was an immediate rival for the established Toyota, Nissan and Mitsubishi turbo engines. Using Subaru’s trademark horizontally opposed engine architecture, the engine doesn’t require a power-sapping balance shaft and, for the first time in a Subaru, the crankcase and heads are constructed from lightweight aluminium. Displacement is a shade under 2-litres thanks to the EJ20’s massively oversquare 92mm bore and 75mm stroke dimensions. Breathing is through a pair of DOHC 4-valve-per-cylinder heads (which make this a quad-cam 16-valve engine). Multi-point fuel injection, coil-on-plug ignition and knock sensing is also employed.

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With an 8.5:1 static compression ratio and a single IHI turbocharger teamed with a water-to-air intercooler system, the five-speed manual ’89 Legacy RS sedan produces 162kW at 6400 rpm and 270Nm at 4000 rpm. However, the auto transmission GT sedan and GT wagon variants (both manual and auto trans) are detuned to 147kW and 260Nm. We believe that output remained the same until the introduction of the twin-turbo engine in 1993.

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In late 1992 the EJ20 turbo engine was also slotted into the GC/GF-series Impreza WRX. In WRX guise, the engine is equipped with an air-to-air intercooler and, in most versions, a larger turbocharger. The static compression ratio remains the same (at 8.5:1). Again, the most powerful engine appeared in the five-speed manual sedan version of the WRX – you’re talking 176kW and 304Nm (at 6000 and 5000 rpm respectively). There was no auto trans option in the early WRX but you could buy a wagon version which was detuned to 162kW/280Nm (which means, at minimum, the WRX engine has equal or greater power and torque compared the contemporary Legacy models).

The Twin-Turbo EJ20 Appears

In late 1993, Subaru split its turbocharged EJ20 into two distinctly different versions – the single turbo version would continue in the Impreza WRX while a new twin-turbo version was introduced to the updated BD/BG-series Legacy GT/RS.

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The single turbo EJ20 engine always had poor bottom-end performance so, to remedy the situation, Subaru developed a sequential twin-turbo arrangement to improve the driveability of the high-performance Legacy (which is considerably heavier than the Impreza). Using a relatively complex control system, the EJ20 TT employs two small capacity turbochargers – the primary turbocharger boosts low rpm torque while the secondary turbocharger chimes in to increase performance at high rpm. The secondary turbo transition (the point where the secondary turbo begins to add intake airflow) is around 4000 – 4500 rpm.

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The twin-turbo engine also brings a completely new pre-turbo intake arrangement and a large top-mount air-to-air intercooler (replacing the water-to-air system previously used in the Legacy RS/GT). With the same 8.5:1 compression ratio coming from forged pistons, the EJ20 twin-turbo can push 184kW but, more importantly, there’s a substantial 309Nm of torque. Output is the same regardless whether you have a sedan or wagon with a manual or auto trans.

Meanwhile, the single turbo engine in the Impreza WRX carried on producing the goods. In late 1994, the five-speed manual sedan was elevated from 176kW at 6000 rpm to 191kW at 6500 rpm. Peak torque also swelled 5Nm. The wagon version remained at 162kW/280Nm.

Nineteen ninety-four also saw the release of the Version 1 and Version 2 STi Impreza. Released early in the year, the Version 1 STi makes 184kW/309Nm while the late ’94 Version 2 STi kicks 202kW/319Nm. These gains come from the fitment of forged pistons, a closed-deck block, lightweight hydraulic lash adjusters (HLAs), a low restriction muffler, improved intercooler plumbing, an intercooler water spray and a revised ECU.

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Two years later, a significant engine revision was performed for the updated MY97 WRX. Altered cylinder heads, an all new inlet manifold, a larger air-to-air intercooler (the same core used on the Legacy twin-turbo) and a different ignition arrangement are the major changes.

At last, these changes enabled the five-speed manual version of the WRX sedan to reach the Japanese regulation output - 206kW. And Subaru hadn’t achieved this high output by sacrificing bottom-end torque – an impressive 329Nm is accessible 1000 rpm lower than previously (at 4000 rpm).

The entire WRX range benefited from the MY97 engine update but, again, the wagon version isn’t as grunty as the sedan. Despite using a 9:1 static compression ratio, the manual and auto trans MY97 wagon makes 176kW/304Nm. In late 1997 (for the MY98), the wagon’s output was bumped up to 184kW/306Nm. Then, in late ’98 (for the MY99), the WRX sedan engine was boosted to 338Nm. A revised intercooler core, revised intake manifold and ECU mods can be thanked for the gain.

The WRX-type engine was also installed into the high-performance Subaru Forester from 1997. Initially, these go-fast Forester models enjoyed the same output as the contemporary WRX – 184kW/306Nm. But in late ’98 (for the ’99 model year), peak power was dropped to 176kW. We believe this is due to the fitment of a pre-turbo cat converter and Tumble Generator Valves (TGVs).

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And what about the evolving STi Subies, you ask?

Well, the MY97 WRX brought the STi Version 3 which incorporates low friction forged pistons and an IHI RHF5 turbocharger. This firecracker produces 206kW (and a bit!) together with 343Nm of torque at 4000 rpm. Next, in late ’97, the STi Version 4 was released with essentially the same engine featuring a bit more boost. Although there is no claimed difference in power, peak torque is increased from 343 to 353Nm.

The MY99 and MY00 Version 5 and 6 STis have exactly the same 206kW/353Nm output but we believe there may have been some minor changes (such as camshaft profile). A limited number of 22B STis were also released in Japan during 1998 – the 22B having a rare 2.2-litre over-bored version of the EJ20 turbo. According to official claims, the 22B generates 360Nm of torque - and peak power is still apparently 206kW...

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Not to be outdone, the Legacy twin-turbo engine met the Japanese regulation 206kW output during 1996. The Legacy GT-B manual wagon runs an 8.5:1 static compression ratio and achieves the ‘golden’ 206kW along with 338Nm of torque. Interestingly, the auto version of the GT-B wagon and all other Legacy GT models (sedan or wagon) use a 9:1 static compression ratio and generate 191kW/319Nm. We believe revisions to the twin-turbo system can be thanked for the improvement.

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Everything remained the same in the Legacy twin-turbo range until the 1998 introduction of the BE/BH-series Legacy. The existing RS/GT identification of the sedan models was dropped and, instead, there’s the B4 RSK sedan. In 1998 Legacy RSK spec, the twin-turbo EJ20 generates 206kW/343Nm in manual guise. The same engine is shared with the contemporary Legacy GT-B manual wagon. Auto versions throughout the Legacy twin-turbo range stay pegged at 191kW/319Nm.

The 2000s

In mid 2000, the GD/GG-series (aka ‘bug-eye’) WRX was introduced in Japan and, for the first time in the EJ20 turbo’s history, power output took a step backward.

With tightening emission standards, Subaru revised many aspects of the engine design and added its Active Valve Control System (AVCS) which, in other words, means variable inlet cam timing. We believe the Tumble Generator Valves (TGVs) are also installed. The MY01 WRX maintains the high 9:1 static compression ratio of late ‘90s Rexes but, still, max power falls to 184kW while torque holds near-constant at 334Nm. These figures apply to WRX sedans and wagons with a manual or auto trans. Curiously, there have been no major changes to the WRX engine up to the current model.

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For real performance in the new series Impreza you need to look at the STi Version 7. With a static compression ratio of just 8:1, AVCS and a large IHI RHF5 turbocharger, the STi Version 7 punches out 206kW at 6400 rpm and 373Nm at 4000 rpm. A six-speed gearbox also comes standard. And if that’s not enough, an update was released in December ’01 bringing 384Nm, another update came in late ’02 bringing 394Nm and yet another update in late ’04 brought a huge 412Nm. A slightly larger intercooler, a twin-scroll turbo, aluminium pistons and other internal mods are incorporated in these running changes. The current STi (with its dramatically new nose) generates 422Nm of torque and, still, peak power is deceptively listed at 206kW.

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The twin-turbo Legacy range continued well into the new millennium. Despite a static compression ratio increase to 9:1, the existing B4 RSK sedan and GT-B wagon continued to generate 206kW/343Nm in manual guise. There were no changes to the auto trans engine (rated at 191kW/319Nm) until the twin-turbo engine was axed in 2003. It appears that it was becoming difficult for the TT engine to meet tightening emission laws.

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For the ’04 model year Subaru replaced the twin huffer engine with a single turbo set-up boasting a fast-response twin-scroll turbine housing and a titanium turbine wheel. A high 9.5:1 static compression ratio and AVCS also contribute to the 206/343Nm output of the manual gearbox Legacy GT. Auto versions produce the same peak torque but top-end power is limited to 191kW. These engines are still current in Japan.

Meanwhile, the go-fast Forester maintained its 176kW/309Nm output until the release of the new-look MY02 version. The Japanese-spec MY02 Forester XT/Cross Sports incorporates AVCS and a 9:1 static compression ratio to deliver a mild 162kW but with a healthy 309Nm of torque. These engines (which are still being sold new) are fitted to either a five-speed manual or four-speed automatic. The current STi Forester is sold with a 2.5-litre engine.

Australian Spec EJ20 Turbo Engines

Be aware that the Australian delivered versions of the EJ20 turbo are very different to their contemporaries in Japan.

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The first EJ20 turbo engine seen in Australia was in the snout of the 1992 Liberty RS sedan and wagon. This engine uses the same water-to-air intercooler arrangement as Japanese models except a lowly 8:1 static compression ratio and conservative tuning drops output to 147kW/260Nm. The Liberty RS disappeared from showrooms during 1994.

In 1994, the first Australian spec WRX was released. Like its Japanese cousin, the Rex engine uses an air-to-air intercooler and a large capacity turbo – but, still, the Australian-spec engine trails by a considerable margin. There’s just 155kW/270Nm instead of 176kW/304Nm.

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The MY97 WRX update (with a completely new inlet system and various other changes) maintains the same 155kW power output but brings it down from 6000 to 5600 rpm. Peak torque is also improved to 290Nm at 4000 rpm. Further alterations to the MY99 WRX bring power up to 160kW and, for the first time, an auto version was available. The manual and auto WRXs have identical engine output.

For the 2001 model year, the GD/GG-series Impreza WRX was introduced. The engine in the new model includes a pre-turbo cat converter, a larger air-to-air intercooler, a larger turbine wheel and wastegate bypass and the cylinder head ports are modified to include Tumble Generator Valves (TGVs). A five-speed manual came standard in the MY01 WRX but a four-speed auto could be optioned for the MY02 WRX. Power output across the MY01 and MY02 WRX is 160kW and there’s 292Nm of torque (at 5600 and 3600 rpm respectively).

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When the bug-eye appearance of the early GD/GG-series WRX was dropped in the MY03 facelift there were also changes under the bonnet. In Australia, the MY03 is the first non-STi WRX to employ the AVCS cam timing system. The compression ratio is also elevated from 8 to 9:1 for improved drivability. This results in an extra 6kW (168kW at 6000 rpm) and torque increases by 3Nm (there’s 300Nm at 3600 rpm). Ninety-eight RON unleaded is recommended for this engine and, for the first time, a sequential automatic transmission was introduced.

WRX output remained the same until the 2005 introduction of the limited edition WRX WRP10. Using an upgrade ECU and free-flow exhaust, output is increased to 175kW (a gain of 8kW over the base WRX). The WRP10 goes into the record books for having the most powerful EJ20 turbo engine in an Australian-spec WRX; the MY06 model uses a 2.5-litre engine.

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In the STi range, Australia first received the MY99 Version 5 two-door and MY00 Version 6 four-door models. These engines retain the Japanese-spec mechanicals but are detuned to suit Australian fuel – so actual output is probably less than the claimed 206kW/353Nm.

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For the ‘02 model year, the bug-eye series STi Version 8 was shipped to Australia (we missed out on the Japanese Version 7 STi). Interestingly, Subaru Australia took extra with the tune of this later model STi engine – instead of generating a claimed 206kW (as previously) output was slashed to 195kW. This was the first EJ20 turbo to appear in Australia with AVCS and an operational intercooler water spray system. There were no mechanical changes in subsequent STi models until the introduction of the 2.5-litre engine in the MY06 STi.

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In took a long while but the twin-turbo EJ20 engine emerged in Australia onboard the MY02 Liberty B4. The Liberty B4 has the same mechanical configuration as the Japanese-spec version but, again, the engine mapping is detuned to suit 98 RON fuel. Output is 190kW and 320Nm - with 278Nm available from just 2000 rpm. A five-speed manual or a four-speed auto was offered. Interestingly, the B4 twin-turbo never got properly established in the Australian marketplace and was axed following the MY03 version.

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Replacing the B4 is the Liberty GT sedan and wagon which were released in late 2003 (for the 2004 model year). The Liberty GT reverts back to a single turbo system together with AVCS cam timing control and a 9.5:1 static compression ratio. There are also numerous internal changes. Output isn’t as strong as the superseded B4 – but it’s not far off. The single turbo Liberty GT pushes 180kW and 310Nm at a low 2400 rpm (just 10kW and 10Nm down on the B4). A five-speed Sportshift auto comes standard in the MY04 Liberty GT – there was no manual option until the MY05 version. The MY05 Liberty GT manual also offers more grunt than the auto versions – 190kW and 330Nm.

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Oh, and don’t forget the local Forester GT which appeared for the 1999 model year. The Forester GT uses a relatively low output version of the EJ20 turbo – it uses an 8.5:1 static compression ratio, a small turbocharger and intercooler, relatively tame camshafts and a conservative ECU tune. Max output is 125kW and there’s 240Nm at just 3200 rpm. A five-speed manual or four-speed auto comes fitted. For the MY01 version output was increased 5kW and 5Nm. This came from altered cylinder head intake ports with Tumble Generator Valves, a larger turbine housing, fitment of a pre-turbo cat converter and updated engine management and ignition systems. The 2.5-litre engine replaces the EJ20 in the current Forester XT.

At the time of writing, the EJ20 turbo is used in only the Liberty/Legacy GT and the Japanese-spec Forester/Cross Sports and Impreza STi. The 2.5-litre engine may be taking over the glamour role but there’s no denying the EJ20 turbo is one of the most important engines in the modern era. And it will continue to prove its worth in the hands of tuners.

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