Subaru EJ16 Tuning

"All you need to know about tuning the Subaru EJ16 engine!"

TorqueCars will examine EJ16 tuning and summarise the ultimate modifications. Subaru EJ16 are fantastic to work on and with the best uprated upgrades like a remap, turbo kits and camshafts you will greatly maximize your driving enjoyment.

History, Power & Specs 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

Tuning the Subaru EJ16 and best EJ16 performance parts.

Best EJ16 upgrades

Just because particular upgrades are are common on EJ16 it doesn't mean its worth having, we shall greatest upgrades that will give your EJ16 the best power gain for you money.

The camshaft profile plays a big part in the engines power output so camshaft upgrades make quite a large difference. The intake & exhaust durations will alter depending on the chosen camshaft profile, so large engines power gains are on offer for camshaft upgrades.

Fast road camshafts normally increase the performance through the rpm band, you may lose a little low down torque but your higher rpm power will be higher.

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

A Motorsport and race cam won't do well if driving around busy urban areas. This is because a competition cam causes a very lumpy idle, and makes the car more prone to stall or jerk along in stop start traffic, sadly though many ignore this and end up ruining a perfectly good car and having to revert back to a fast road, or OEM cam profile.

You should ideally optimize your torque band to your typical driving style so for a car driven daily stick with a fast road EJ16 cam

Different EJ16 engines respond better to more or less aggressive cam durations so view each engine as unique.

The map and fuel pump and injectors also will make differences on the power gains you'll get.

Longer valve 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.

Typical stage 1 mods often include: Intake headers, Remaps/piggy back ECU, Panel air filters, Sports exhaust manifold, Fast road camshaft, drilled & smoothed airbox.

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

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

The EJ16 units are fantastic to work on and we see that there are quite a few choices of modifications and performance parts around.

ECU flashing should help to to establish the full potential of all the parts you've fitted to your EJ16.

(In some cases, as the factory ECU is locked flashing is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it setup properly.)

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

Forcing air into each cylinder is vital to any performance tuning job.

Headers flow the air during the suck phase from the filter and allow it to be drawn into the engine cylinders with fuel for the squish phase.

The size of bore and shape and flow characteristics of the Intake manifold can make a noticeable effect on to fuel delivery on the EJ16.

Many mass produced engine air intake manifolds are ripe for aftermarket tuning parts, although a few makers provide decently flowing air intake manifolds.

Larger EJ16 valves, carrying out 3 or 5 angle valve jobs and porting and head flowing will also raise bhp, and significantly will allow you to get raising the bhp increase on other 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 EJ16 but we don't think it is worth the effort or cost.

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

Research these limits and install better quality components to utilize the power.

We see many tuners spending a lots of money on turbo upgrades on the EJ16 only to watch the engine block go up in smoke just after it's first rolling road session.

It is not unusual that there is a restriction in the air flow sensor AFM/MAF on the EJ16 when considerably 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 sapped bhp and torque at a much lower level.

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


When you increase the power you will need to uprate to the fuel system.

More power needs more fuel. We would recommend you to be generous with your flow rate on the injectors.

The accepted safe increase is to add another 20% when fitting an injector, this accounts for injector deterioration and affords a little 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.

All the following flywheel power targets will assume an injector duty cycle of 80% and a base of 58psi of fuel pressure at idle.

4 Cylinder turbocharged engines

  • 58 PSI 340cc/min 200hp
  • 58 PSI 511cc/min 300hp

4 Cylinder NASP engines

  • 58 PSI 285cc/min 200hp
  • 58 PSI 426cc/min 300hp


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

On most factory exhausts you'll find the 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 out of the engine but do not go too large or you could very well end up with a reduced flow rate. So generally speaking, keep to 1.5 to 2.5 inches as a rule of thumb.

Typically exhaust restrictions can be located the catalyst and filters installed, so adding a better flowing race alternative such as a sports catalyst pretty much removes this restriction, thanks to it's larger size and surface area, and will effectively raise the performance to levels you would expect without having a catalyst installed, but keeps the car road legal.

Weak spots Issues & problem areas on the EJ16

The EJ16 engines are generally reliable and solid as long as they are regularly serviced and maintained.

Carbon build up in the head, particularly around the valves which will sap power or create flat spots, this is a larger issue on direct injection engines but should be looked out for on all engines. We have tips on removing carbon build up.

Some of our members have had issues with flat spots or glitches after applying mods and upgrades or tuning, this is not usually related to this engines design, so instead see our article on diagnosing flat spots and problems after tuning which should help you get the bottom of this issue.

Regular oil changes are vital on the EJ16, especially when tuned and will help extend the life and reliability of the engine.

If you would like to know more, or just get some friendly advice 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.

Please help us improve these tips by sending us your feedback in the comments box below.

We love to hear what our visitors have got up to and which tuning mods work best for them on each model of car. Comments are used to improve the accuracy of these EJ16 articles which are continually updated.

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