Tuning the Subaru EJ20

"Comprehensive guide to tuning the Subaru EJ20 engine!"

The Subaru EJ20 provide a fun base for your project and with the ultimate performance modifications like remaps, turbo kits and camshafts you will greatly maximize your driving fun.

TorqueCars will look into EJ20 tuning and provide tips on the best modifications for your car.

Just because particular mods are are common on EJ20 it doesn't mean its worth having, instead we will focus mods that will give your EJ20 the best power gain for you money.

Altering your EJ20 cam will make a dramatic difference to the engine torque. Choosing a higher performance cam profile raises the torque accordingly.

NB: Fast road cams usually raise the bhp throughout the rev band, you might lose a little low end power but your high end rpm power will improve.

Competition cams, raise the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

In a daily driver must carefully try to optimize your engines power to your usage of the car.

You will never find a EJ20 Race cam is a pleasure to live with when on the daily commute.

Each engine responds better to more aggressive cam durations check your engine on a rolling road.

The ECU mapping and fuelling also have an effect on the power gains you'll make.

Extending exhaust or intake durations can alter the power band and on most engines the exhaust and intake durations do not need to match, although most cams and tuners use matched pairs there are some advantages to extending the intake or exhaust durations.

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Stages of Tune

Stage 1 mods: Drilled & smoothed airbox, Sports exhaust manifold, Fast road camshaft, Remaps/piggy back ECU, Panel air filters, Intake headers.

Stage 2 mods: fuel pump upgrades, high flow fuel injectors, induction kit, Fast road cam, Sports catalyst & performance exhaust, Ported and polished head.

Stage 3 mods: Engine balancing & blueprinting, Competition cam, Twin charging conversions, Crank and Piston upgrades to alter compression, Internal engine upgrades (head flowing porting/bigger valves), Adding or Upgrading forced induction (turbo/supercharger).

ECU flashing should help to release the full potential of all the tuning parts you've fitted to your EJ20.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but power output will depend much on the tuning parts you've carried out and the condition of your engine.

We found the following spec list for the EJ20 engine which has been compiled from the most popular mods.

• Garrett T04E/T3 Ball-Bearing Turbocharger
• 3" Downpipe (Cat can be removed for off road use) (For T3/T04E Turbo)
• Cold Air Intake K&N Filter (For T3/T04E Turbo)
• HKS Racing External Wastegate
• Up-Pipe (Cat-Less) (For T3/T04E Turbo and HKS Wastegate)
• 785cc Fuel Injectors with the resistor pack

Other options include the PE1820 or VF30 and a FMIC is a good idea, the top mount position is not the most efficient design out there.

It is vital to any engine performance tuning project to feed more fuel and air into each cylinder

The intake plenum transmit the air during the suck phase from the air filter and allow it to be sucked into the engine cylinders with fuel for the squish phase.

Design and flow characteristics of the Intake manifold can make a substantial difference to to fuel atomisation and engine efficiency on the EJ20.

I usually find intake manifold are crying out for aftermarket tuning parts, although a few car makers provide reasonably good intake manifold.

Adding a EJ20 larger valve kit, doing some port work and head flowing will also raise bhp and torque, and more importantly will make space for a better bhp and torque increase on other tuning parts.

Turbo upgrades

NASP engines need quite a lot of work when you add a turbo, so we have a separate guide to help you take into account the pros and cons of going this route on your EJ20

The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes major power gains.

If the engine is fitted with a turbo parts are giving better power gains and you will discover turbocharged engines are built using uprated components.

There are practical limits for every engine, with some being extremely strong and some only able to handle stock power

Discover these restrictions and fit better quality components to handle the power.

We've seen tuners spending a fortune on turbo upgrades on the EJ20 only to suffer the indignity of watching the motor explode just after it's used on the roads.

Big turbochargers tend to experience no power at low rpm, and little turbochargers spool up more quickly but don't have the peak end power band gains.

Thankfully the world of turbo chargers is always moving on and we now see variable vane turbo chargers, where the vane profile is altered according to speed to lower lag and increase top end bhp.

Twin scroll turbo chargers divert the exhaust gases into a couple of channels and flow these at differently profiled vanes in the turbo charger. They also improve the scavenging effect of the engine.

You'll commonly see there is a limit in the air flow sensor MAP/MAF/AFM on the EJ20 when loads more air is being fed into the engine.

We note 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped torque at a much lower level.

Adding a supercharger or additional turbo will make large performance gains, although harder to setup. We have this feature on twinchargers if you want to read more.

Fuelling upgrades and mods

You will need to ensure that the engine is not starved of fuel so will need to ramp up the fuelling when you start going beyond 20% of a bhp and torque increase.

The Walbro 255 pump is a good solid option for most projects.

We strongly recommend you to be generous with your injector capacity.

As a rule of thumb add 20% capacity when fitting an injector, which takes into account injector deterioration and affords a bit of spare capacity should the engine require more fuel.

We think this one is common sense, but you'll need to match your fuel injector to the type of fuel your car uses as well.

Exhaust upgrades and mods

You should look to uprate your exhaust if the current exhaust is creating a restriction.

On most factory exhausts you should find that the flow rate is still good even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Don't go with the largest exhaust you can buy this will reduce the exhaust flow rate - the best exhausts for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Usual exhaust restrictions come around the catalysts installed, so adding a higher flowing high performance alternative will help avoid this restriction.

Weak spots, Issues & common problem areas on the EJ20

Camshaft cover seals regularly fail, so should be examined and replaced to avoid leaks.

The water cooling supply to cylinder 4 is not as good as to the others, so it will typically fail first. The first sign of a problem is an engine tapping noise, sadly a strip down and repair is the only option here.

The Turbocharged engines such as the EJ20G, EJ205 and the EJ20K are quite highly tuned, and need to be treated with care and regularly maintained.

As piston rings wear they can seep and this results in high oil consumption and burning of oil. Check the exhaust for blue smoke.

The EJ20 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the EJ20, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

History of the Engine

EJ20E SOHC naturally aspirated

• Legacy JDM '89-'94
  125ps (92kw 123hp )
  BC - BF series
  '93-'99 135ps (99kw 133hp )
  BD - BG series( ECU code EURO, D3 Asia 4H)
  '98- '04 155ps (114kw 153hp )
  BE - BH series( ECU code EURO, D3 Asia 4H)
  '03- '09 140ps (103kw 138hp )
  BL - BP series Europe
  '91-'99 115ps (85kw 113hp )
  BC, BD, BF series
• Impreza JDM'93-'99
  135ps (99kw 133hp )
  GC - GF series
  '08-current 140ps (103kw 138hp )
  GH - GE series
  Europe
  '94-'99 115ps(85kw 113 hp)
  GC, GF series
  Isuzu Aska ('90–'93)'90-'93 125ps (92kw 123hp )

EJ201

• Subaru BE/BH Liberty
  92kW @5600rpm184Nm at 3600rpm '98-03
• Subaru GD/GG Impreza
  92kW @5600rpm 184Nm at 3600rpm '00-03

EJ20D DOHC naturally aspirated

• Legacy JDM '89-'99 150ps (110kw 148hp ) BC - BF and BD - BG series

EJ202 SOHC naturally aspirated

• Forester JDM SF series, 138ps('97 - '02)

EJ203 SOHC naturally aspirated

• Forester JDM SG series, 140ps( '03 - '08)
• Legacy JDM 2.0i BP/BL series, 140ps( '03 - '09)
• EJ204 DOHC naturally aspirated AVCS
• Legacy B4 TSR JDM BE - BH series'99- '01 155ps (114kw 153hp )
• Legacy JDM BL - BP series '03- '09 190ps (140kw 187hp )
• Legacy (Europe) BL - BP series '03- '07 165ps (121kw 163hp )
• Impreza JDM GC - GF series'93-'99 155ps (114kw 153hp )
• Impreza GE - GH series '07-2011 150ps (110kw 148hp )
• Forester (Europe) SG Series '05- '07 158ps (116kw 156hp )
• Forester JDM SH Series '08-2011 150ps (110kw 148hp )
• Exiga JDM YA Series '08 - 2012 150ps (110kw 148hp )

Rocker-style HLA EJ20G

• Legacy RS 89-93
• Legacy RS-RA 89-93

Bucket-style HLA EJ20G

• Impreza WRX 92-96
• Impreza WRX Wagon 92-96Impreza WRX Wagon AT 96-98
• Subaru Impreza WRX RA 93-96
• EUDM Subaru Impreza Turbo 94-96

Closed deck

• EJ20GDW1HD '92-May to '93-Aug WRX.EJ20G
• EJ20GDW1HE '92-May to '93-Aug WRX.EJ20G
• EJ20GDW1HJ '92-May to '93-Aug WRXRA.EJ20G
• EJ20GDW1HR '92-May to '93-Aug WRXRA.EJ20G
• EJ20GDW2HD '93-May to '94-Sep S.WRX.MT.EJ20G
• EJ20GDW2HE '93-May to '94-Sep S.WRX.MT.EJ20G
• EJ20GDW2HJ '93-May to '94-Sep WRXRA.EJ20G
• EJ20GDW2HR '93-May to '94-Sep WRXRA.EJ20G
• EJ20GDW4HJ '93-Jun to '95-Aug WRXRA.EJ20G
• EJ20GDW5HJ '95-Sep to '96-Aug WRXRA.EJ20G (STI)

Open deck

• EJ20GDX1ND '93-May to '94-Sep AT.EJ20G
• EJ20GDX1NE '93-May to '94-Sep AT.EJ20G
• EJ20GDW1ND '93-May to '94-Sep W.MT.EJ20G
• EJ20GDW1NE '93-May to '94-Sep W.MT.EJ20G
• EJ20GDW4HD '94-Jun to '95-Aug S.WRX.EJ20G
• EJ20GDW4HE '94-Jun to '95-Aug S.WRX.EJ20G
• EJ20GDW4ND '94-Jun to '95-Aug W.WRX.MT.EJ20G
• EJ20GDW4NE '94-Jun to '95-Aug W.WRX.MT.EJ20G
• EJ20GDX4NE '94-Jun to '95-Aug WRX.AT.EJ20G
• EJ20GDW5HE '95-Sep to '96-Aug S.WRX.EJ20G
• EJ20GDW5NE '95-Sep to '96-Aug W.WRX.MT.EJ20G
• EJ20GDX5NE '95-Sep to '96-Aug AT.EJ20G
• EJ20GDX5HD '95-Sep to '96-Aug S.WRX.EJ20G
• EJ20GDW5PE '95-Oct to '96-Aug W.WRX.MT.EJ20G (STI)
• EJ20GDW5PE '95-Oct to '96-Aug WRXSTI.EJ20G
• EJ20GDW5PJ '95-Oct to '96-Aug WRXRASTI.EJ20G

EJ20K

EJ20K engines fall into either shim under or shim over bucket design

Shim-over-bucket style EJ20K usage

• JDM WRX 96-97
• Impreza WRX wagon MT '97-'98
• Impreza WRX type RA or R MT '97-'98

Shim-under-bucket style EJ20K usage

• Impreza WRX STI MT 97-98
• Impreza WRX STI wagon MT 97-98
• Impreza WRX STI type RA or R MT 97-98

EJ205

• Impreza WRX
• 99-01 (JDM Wagon Body only)
• 01-06 (all JDM)
• 02-05 (USDM)
• 05 SAAB 9-2X AERO
• 99-06 (all other markets)
• Forester Cross Sports, S/tb, STI

EJ20H EJ20R EJ206 and EJ208 were fitted to the Legacy and each had differences, with the EJ208 regarded as a new engine design thanks to revised Camshaft, intake manifold injectors and fuel/timing.

NOTE: EJ20T and EJ20TT were not official engine codes, they were used by customers to describe the Tubo and Twin Turbo engines in high performance models.

For more information on Tuning your EJ20 engine please join us in our friendly forum where you can discuss tuning options in more detail with our worldwide members with the EJ20 engine, or read our ej20 tuning articles to get a full grasp of the benefits and drawbacks of each modification.

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This article is flagged for an update, so please pass on specific tips below that I can include. All articles, and content was written by me, Waynne Smith TorqueCars founder. Some outlines are just too general so I appreciate your feedback and suggestions. This entry was filed under Subaru. You can leave a response below or join our forum to discuss this article and car modification in detail with our members.

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