Tuning the Subaru EJ18

"Comprehensive guide to tuning the Subaru EJ18 engine!"

Our aim here is to look at EJ18 tuning and provide tips on the premier modifications for your car. Subaru EJ18 are awesome to work on and with a few sensible motorsport upgrades like ECU maps, turbo improvements and camshafts you will certainly increase your driving experience.

When talking about the best greatest for your EJ18 engine, we are going to focus on the upgrades that give the best value for money.

Significant gains on the EJ18 can be made from camshaft upgrades. Altering the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the bhp and power output.

NB: Fast road cams normally raise the bhp throughout the rev band, you could drop a little low end power but higher rpm power will be better.

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

On a daily driver must carefully try to match your engines power to your cars usage.

I'd be amazed if you have ever thought a EJ18 Race cam is a pleasure to live with when driving in heavy traffic.

Different EJ18 engines respond better to more aggressive camshaft durations so set your engine up on a rolling road.

The ecu map and injectors and fuel pump also will make differences on the torque gains you'll achieve.

Extending exhaust or intake durations can alter the torque 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: Fast road camshaft, Intake headers, Sports exhaust manifold, Drilled & smoothed airbox, Remaps/piggy back ECU, Panel air filters.

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

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

ECU flashing helps release the full potential of all the upgrades you've fitted to your EJ18.

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 often differs on the upgrades you've fitted and the condition of your engine.

It is the main goal to any tuning task to force more air into your EJ18

Headers take the air from the air cleaner and allow it to be fed into the engine cylinders.

The shape and rate of flow of the Intake headers can make a big change to fuel atomisation on the EJ18.

Commonly we find the intake manifold are improved through aftermarket tuning parts, although some OEM provide decently flowing intake manifold.

Adding a EJ18 larger valve kit, doing some 3 or 5 angle valve jobs and porting and head flowing will also improve power, & more importantly will afford you a better power increase on other mods.

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 EJ18

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

When your car is fitted with a turbocharger parts are more reliable and we find turbo engines are built with better components.

There are reliable limits for every engine, with some being incredibly solid and some only just able to handle stock power

Discover these limits and fit forged components to survive the power.

There are many guys spending a fortune on turbocharger upgrades on the EJ18 only to suffer the indignity of watching the car go up in smoke just after it's completed.

Big upgraded turbos will usually experience a bottom end lag, and smaller turbos spool up more quickly but do not have the high rpm bhp gains.

Thanks to new tech the range of turbo chargers is always moving on and we are seeing variable vane turbo chargers, where the vane angle is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbo chargers divert the exhaust flow into 2 channels and flow these at differently profiled vanes in the turbocharger. They also boost the scavenging effect of the engine.

You'll commonly see there's a limitation in the air flow sensor AFM/MAP on the EJ18 when a lot more air is being drawn into the engine.

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

Adding a supercharger or additional turbo will make large bhp gains, although more difficult to configure. We have this guide to 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 pay attention to the fuelling when you start going beyond 20% of a power increase.Don't forget to over specify your injectors flow rate.

As a rule of thumb add 20% capacity when buying an injector, which takes into account injector deterioration and gives 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 existing exhaust is actually creating a restriction.

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

Sports exhausts generally help improve air flow through the engine but do not go too large or you may end up will reduce the flow rate. Stick to 1.5 to 2.5 inches as a rule of thumb.

Common exhaust restrictions come around the catalyst installed, so adding a better flowing sports alternative will help avoid this restriction.

Weak spots, Issues & common problem areas on the EJ18

The EJ18 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the EJ18, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

History of the Engine

• Impreza 93-99 GC6 series
• Legacy (except USA) 90-96 BC2, BC3, BD2, BD3, BG3 series
• Isuzu Aska (1990–1993)

EJ181

• 108 bhp @6000 rpm 110 lbft @ 3200 rpm

EJ182

•  113 bhp @ 6000 rpm 114 lbft @4500 rpm

EJ183

•  118 bhp @5600 rpm 121 lbft @3600 rpm

For more information on Tuning your EJ18 engine please join us in our friendly forum where you can discuss tuning options in more detail with our worldwide members with the EJ18 engine, or read our ej18 tuning articles  to get a full grasp of the benefits and drawbacks of each modification.

We need your help improving this article, so please send us your feedback in the comments box below and pass on any tips, points or facts we have wrong or have not covered.

We really like hearing from our readers, and hearing about which modifications were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our EJ18 guides and tips are kept up to date.

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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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