Tuning the Subaru EJ16

"Comprehensive guide to tuning the Subaru EJ16 engine!"

We shall provide a guide to EJ16 tuning and provide tips on the best mods that work. Subaru EJ16 are popular tuning projects and with the right enhancements like a remap, turbo upgrades and camshafts you will really improve your driving pleasure.

The ultimate EJ16 upgrades on an engine are as we have found the ones that give the best value for money.

We won't be swayed by popular EJ16 upgrades, they need to be cost effective.

Significant gains on the EJ16 can be made from cam upgrades. Altering the cam profile alters the intake and exhaust durations on the engine and can dramatically change the torque and power output.

NB: Fast road cams normally increase the power across the rpm band, you may lose a little bottom end torque but higher rpm power will improve.

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

On a road car must carefully try to match your engines power to your driving style.

I'd never have found a EJ16 Race camshaft is a pleasure to live with when driving around busy urban areas.

Different EJ16 engines respond better to mild cam durations check your engine on a rolling road.

The engine timing and injectors and fuel pump also will make differences on the bhp gains you'll make.

Longer valve durations can alter the bhp 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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Guide to the Best Tuning Mods & Upgrades

  1. Mods that Remove a Restriction

    If the intake or exhaust are restricted in any way this will have an impact on your cars performance, so use an induction kit/filter upgrade and better flowing exhaust whenever your tuning creates a flow restriction.

  2. Mods that Improve Handling

    Braking, Suspension and general alignment of the suspension components is vital for any tuning project even before you start increasing power.

  3. Fit Stronger Parts

    Tuned cars will show up weaknesses, typically in the turbochargers, clutch and internal engine components. Whilst most engines can cope with mild tuning mods, TorqueCars recommend that you upgrade the internal components before these weak spots manifest themselves.

  4. ECU Tunes & Remapping

    While some cars can be easily remapped, others may require piggyback ECU's or aftermarket ECU's but this is the most vital step of your tuning project as it fully releases the power from all of your mods and upgrades. Expect 10-20% on NASP engines and 30-40% on turbocharged units.

  5. More Power Needs More Fuel & Air

    Every tuning project will aim to increase the air supply, but fuel supply is just as vital and will need to match the air the engine can utilise. Fuel to Air ratio is vital so upgrade the fuel pump & injectors. Also you can look to perform head mods (flowing and porting), bigger valves, fast road cams and forced induction upgrades to improve fuel.

Stages of Tune

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

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

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

Review your options and then buy your tuning parts and set yourself a power target to avoid wasting your time and money.

ECU mapping helps fully realize the full potential of all the parts you've fitted to your EJ16.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but the outcome will rely on the parts you've done and the condition of your engine.

Feeding fuel and air into each cylinder is the main goal to any engine performance tuning job.

The intake plenum carry 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.

The shape and rate of flow of the Intake manifold can make a noticeable improvement to fuel atomisation and engine efficiency on the EJ16.

We often see plenum chambers are needing motorsport parts, although some car makers provide decently flowing plenum chambers.

Fitting big valve kits, carrying out EJ16 port enlargement and head flowing will also improve power, and significantly will make space for a greater power increase on other upgrades.

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 EJ16

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 a car is fitted with a turbocharger tuning parts are going to make more power and most turbo engines use harder and stronger components.

However you will find an engines have limits

See where you'll find these restrictions and upgrade to forged components to handle the power.

We see many car owners spending a loads on turbocharger upgrades on the EJ16 only to see the car throw a rod when it's been enthusiastically driven.

Larger turbo units commonly suffer low end lag, and little turbo units spool up much more quickly but do not have the peak end engines power gains.

In recent times the choice of turbos is always evolving and we commonly find variable vane turbos, allowing the vane profile is altered according to speed to lower lag and increase top end performance.

Twin scroll turbos divert the exhaust gases into two channels and feed these at differently angled vanes in the turbo. They also help the scavenging effect of the engine.

You'll commonly see there is a limit in the air flow sensor MAF/MAP on the EJ16 when a lot more air is being drawn into the engine.

Going up you'll find 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor limited performance at a much lower level.

Adding a supercharger or additional turbo will make large bhp gains, although more challenging to configure. We have this article covering twinchargers if you want to read more.

Fuelling upgrades and mods

Don't miss you'll need to ramp up the fuel system when you are increasing the torque - it makes the car more thirsty. Don't forget to over specify your flow rate on the injectors.

The accepted safe increase is to add 20% to the flow rate when specifying an injector, this accounts for injector deterioration and gives you some 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 increase your exhaust if your exhaust is actually creating a restriction in flow.

On most factory exhausts you should find that your flow rate is still fine 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 biggest exhaust you can get you'll slow the exhaust rate - the best for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

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

Weak spots, Issues & common problem areas on the EJ16

The EJ16 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the EJ16, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

History of the Engine

  • Impreza 93-94 (JDM only) GC4 series
  • Impreza 93-06 (Europe & Middle East)
  • Impreza 93-97 (Australia)
  • Impreza 93-06 (Latin America)
  •  89–97 bhp @6000 rpm  102 lbft at 4500 rpm

For more information on Tuning your EJ16 engine please join us in our friendly forum where you can discuss tuning options in more detail with our worldwide members with the EJ16 engine, or read our ej16 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 tuning mods were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our EJ16 guides and tips are kept up to date.

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