Subaru EJ15 Tuning

"All you need to know about performance tuning the Subaru EJ15 engine!"

The Subaru EJ15 are good project engines and with the ultimate uprated modifications like remapping, turbo kits and camshafts you will substantially increase your driving experience.

Let us examine the options for your EJ15 tuning and summarise the best modifications.

We look into EJ15 tuning and show the premier upgrades.

History of the Engine

EJ151

  • 96 bhp at 6000 rpm 95 lbft at 3600 rpm

EJ152

  • 101 bhp at 5600 rpm 101 lbft at 4000 rpm

EJ153

  • 94 bhp at 5200 rpm 103 lbft at 3600 rpm

EJ154

  • 99 bhp at 5200 rpm 105 lbft at 4000 rpm

Tuning the Subaru EJ15 and best EJ15 performance parts.

Best EJ15 tuning mods

Just because particular tuning parts are are common on EJ15 it doesn't mean you should fit it, we shall focus tuning parts that will give your EJ15 the biggest power gain return for your cash.

Significant gains on the EJ15 can be made from camshaft upgrades. Altering the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the power band and power output.

Fast road camshafts commonly increase the bhp through the rev band, you could sacrifice a little low down power but the top end will be better.

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

For a car used daily should ideally to optimize your engines power to your usage of the car.

I'd be shocked find a EJ15 Motorsport cam is a pleasure to live with when driving around busy urban areas.

Some EJ15 engines respond better to extreme camshaft durations check your engine on a rolling road.

The engine timing and injectors and fuel pump also will say much on the torque gains you'll make.

Altering valve 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.

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

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

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

The EJ15 engines are great to work on and thankfully there is an increase of mods and performance parts out there.

Remaps will help unlock the full potential of all the tuning parts you've done to your EJ15.

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

It is the whole point to any engine performance tuning project to push fuel and air into your EJ15

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

Design and rate of flow of the Intake headers can make a big change to fuel mixing and power on the EJ15.

Commonly we find the intake headers are improved through aftermarket parts, although some manufacturers provide fairly well optimized intake headers.

Larger EJ15 valves, doing some EJ15 port enlargement and head flowing will also improve bhp and torque, and importantly will give you an improved bhp and torque 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 EJ15

Frankly the work required to turbocharge and EJ15 could be much better spent elsewhere.

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.

It is important to find these limits and fit better pistons and crank to cope with the power.

We see many car owners spending a lots of money on turbo charger upgrades on the EJ15 only to experience the motor go up in smoke soon after it's finished.

Large capacity turbo chargers tend to suffer a bottom end lag, and small turbo chargers spool up much more quickly but won't have the high rpm torque gains.

Over the last 20 years the choice of turbo chargers is always increasing and we are seeing variable vane turbo chargers, where the vane profile is altered according to speed to lower lag and increase top end performance.

You'll commonly see there is a restriction in the air flow sensor (AFM/MAF/MAP) on the EJ15 when considerably more air is being sucked into the engine.

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

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

Fuelling

Don't forget to look at the fuelling when you are increasing the power - it makes the car more thirsty. It makes sense to over specify your injector capacity.

The accepted safe increase is to add 20% to the flow rate when specifying an injector, this takes into account injector deterioration and gives you some spare capacity should the engine need 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 NASP engines

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

Exhaust

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

On most factory exhausts you'll find the exhaust 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.

Please dont run with the biggest exhaust you can find this will slow up 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.

Typically exhaust restrictions are in the emissions filters installed, so adding a better flowing performance alternative will help avoid this restriction.

Weak spots Issues & problem areas on the EJ15

The EJ15 engines are generally reliable and solid as long as they are regularly serviced and maintained.

Regular oil changes are vital on the EJ15, especially when tuned and will help extend the life and reliability of the engine.

For more information on Tuning your EJ15 engine please join us in our friendly forum where you can discuss tuning options in more detail with our worldwide members with the EJ15 engine, or read our ej15 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 modifications work best for them on each model of car. Comments are used to improve the accuracy of these EJ15 articles which are continually updated.

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