Subaru EJ22 Tuning

"All you need to know about tuning the Subaru EJ22 engine!"

The Subaru EJ22 are awesome to work on and with the ultimate performance upgrades like remapping, turbo upgrades and camshafts you will maximise your driving fun.

In this article we examine EJ22 tuning and show the premier modifications for your car.

History, Power & Specs of the Engine

EJ22E Naturally Aspirated


  •  130 bhp (97 kW 132 PS) at 5800 rpm  (137 lbft) at 4800 rpm


  •  135 bhp (101 kW 137 PS) at 5800 rpm 140 lbft) at 4800 rpm


  • 137 bhp (102 kW 139 PS) at 5400 rpm  (145 lbft) at 4000 rpm

('89-97 Australia)

  • 100 kW (134 hp 136 PS) at 6000 rpm  (139 lbft) at 4800 rpm

EJ222 Naturally Aspirated (1999-2001)

  • 142 bhp (106 kW 144 PS) at 5600 rpm (149 lbft) at 3600 rpm


  •  183 bhp (136 kW 186 PS) fully closed deck
    Legacy 1991-1994


  • 280 PS (206 kW 276 bhp) at 6000 rpm 268 lbft at 3200 rpm
    Impreza STi 22B GC8 series (JDM)

Tuning the Subaru EJ22 and best EJ22 performance parts.

Best EJ22 upgrades

Just because particular upgrades are are common on EJ22 it doesn't mean its worth having, instead we'll best upgrades that will give your EJ22 the best power gain for you money.

Significant gains on the EJ22 can be made from cam upgrades. Altering the cam profile alters the intake and exhaust durations on the engine and can dramatically change the engines power and power output.

Fast road cams commonly increase the bhp over the rev range, you could drop a little bottom end torque but the higher rpm power will be lifted.

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 you need to match your engines power to your driving style.

I'd be amazed if you have ever thought or claimed that a EJ22 Motorsport camshaft is a pleasure to live with when driving in heavy traffic. The low end idle will be very lumpy and irregular, so something you would notice on a track when you drive in the upper third of the rpm band, but on roads this is a serious issue and we've heard from lots of drivers lamenting their decision to add an extreme competition cam profile to their engine.

Some EJ22 engines respond better to more or less aggressive camshaft durations so view each engine as unique.

The ECU mapping and injectors and fuel pump also will say much on the power gains you'll hit.

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.

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Best Engine Mods for your car

  1. Mapping - remapping provides the most advantage in terms of cost savings,  aftermarket ECUs, and piggyback ECUs are all alternatives.
  2. Fast road cams are one of the most significant mechanical changes, but they must be installed by someone who knows what they're doing and they are not always easy to source but you might find a local firm to regrind a stock camshaft.
  3. Intake and Exhaust - Note that on their own these mods will NOT ADD POWER in most cases, but they can help enhance power after other mods by removing the restriction.
  4. Upgrades to turbochargers and superchargers - forced induction is the most efficient approach to increase air supply, allowing you to burn more fuel and make more power. It is one of the most costly upgrades but provides the best gains.
  5. Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.

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

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

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

The EJ22 engines respond well to upgrades and we're happy to report there is a growing number of parts and performance parts out there.

Mapping should help to fully realize the full potential of all the upgrades you've fitted to your EJ22.

(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 NA (naturally aspirated) engines, but your results will rely on the upgrades you've carried out and the condition of your engine.

Pushing air into the EJ22 engine is the main goal to any engine modification job.

Intake take the air from the intake filter and allow it to be drawn into the engine and mixed with fuel.

The bore size, shape and flow rate of the Air Intake manifolds can make a large effect on to fuel atomisation on the EJ22.

Most air intake manifolds are begging for aftermarket tuning parts, although some car makers provide reasonably well designed air intake manifolds.

Increasing the EJ22 valve size, getting EJ22 port enlargement and head flowing will also lift performance, & more importantly will afford you a better performance increase on other upgrades.

Turbo upgrades

NA (naturally aspirated) 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 EJ22

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

If an engine has forced induction parts are going to net you a larger power gain and you'll see that turbocharged engines are made using better components.

However you will find an engines will have power limits

It is important to find these limitations and fit better pistons and crank to survive the power.

There are many people spending a lot of money on turbo upgrades on the EJ22 only to watch the engine explode just after it's been enthusiastically driven.

Large turbos tend to suffer no power at low rpm, and smaller turbos spool up more quickly but do not have the top end engines power gains.

Over the last 20 years the market of turbochargers is always evolving and we commonly find variable vane turbochargers, allowing the vane profile is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbochargers divert the exhaust gases into 2 channels and feed these at differently designed vanes in the turbo charger. They also boost the scavenging effect of the engine.

It is common that there is a limitation in the air flow sensor AFM/MAF on the EJ22 when loads more air is being sucked into the engine.

You'll see that 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor limited bhp and torque at a much lower level.

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


When you increase the torque you will need to uprate to the fuel delivery.

More torque needs more fuel. We would recommend you to over specify your injector capacity.

As a rule of thumb add 20% capacity when specifying an injector, this 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.

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
  • 58 PSI 682cc/min 400hp
  • 58 PSI 1022cc/min 600hp

4 Cylinder NA (naturally aspirated) engines

  • 58 PSI 285cc/min 200hp
  • 58 PSI 426cc/min 300hp
  • 58 PSI 568cc/min 400hp
  • 58 PSI 853cc/min 600hp


You may need to upgrade your exhaust if your current exhaust is creating a flow problem.

On most factory exhausts you should find that your 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.

Sports exhausts can help balance the flow of gases through the engine.

But if your exhaust pipe is too large, ie: it's over 2.5 inches bore, you will lose much of the exhaust flow rate and end up lacking power and torque.

Common exhaust restrictions come around the 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 EJ22

The EJ22 engines are generally reliable and solid units, as long as you follow the manufacturers service schedules, and use a good quality oil to ensure longevity. Few problems should happen 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 EJ22, 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 EJ22 engine please join us in our friendly forum where you can discuss tuning options in more detail with our tuning articles to get a full grasp of the benefits and drawbacks of each modification.

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