Modding tuning and best performance upgrades on the Subaru EJ15 engine!

The Lowdown on "EJ15 Modifications"

How to modify and upgrade the Subaru EJ15

"Comprehensive guide to performance parts and tuning the Subaru EJ15 engine!"

Popular tuning sites like TorqueCars are frequently getting messages requesting info on how to improve the EJ15 from people wanting to know what are the things tuners are recommending when it comes to EJ15 mods that work. So let us look into Subaru EJ15 parts and outline the best modifications on this great engine and point out some problems along the way.

Now we will review and look at EJ15 tuning and provide tips on the optimum modifications. Subaru EJ15 have loads of potential and with the ultimate motorsport parts like a remap, turbo improvements and camshafts you will dramatically improve your driving opportunities.

When talking about the optimum parts for your EJ15 engine, we are going to concentrate on the tuning parts that give the biggest return for your cash.

EJ15 induction kits

Improving air intake on the EJ15

You need air and fuel for an engine to work. If there is little supply of fuel then it will run lean, if there is not enough air it runs rich losing power which risks damage to the EJ15. We'll pick up on fuelling later in this article but for now we shall look at air supply.

So Getting air into your EJ15 is the primary aim to any engine modification project.

It is not unusual that there is a limitation in the air flow sensor AFM/MAP on the EJ15 when a lot more air is being drawn into the engine.

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

Engines intake headers transmit the air from the air filter and allow it to be drawn into the engine cylinders.

Design and rate of flow of the Intake headers can make a big improvement to fuel engine efficiency on the EJ15.

We often see plenum chambers are begging for a performance upgrade, although some car makers provide reasonably good plenum chambers.

Increasing the EJ15 valve size, doing a bit of EJ15 port enlargement and head flowing will also boost torque, and importantly will allow you to get a better torque increase on other upgrades.

EJ15 performance cam tips.

Different EJ15 engines respond better to different cam durations so view each engine as unique.

The ecu map and injectors and fuel pump also will say much on the bhp gains you'll achieve.

Altering 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.

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 power band gains are on offer for camshaft upgrades.

NB: Fast road camshafts usually raise the power through the rpm range, you could sacrifice a little low down torque but top end will be better.

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

In a daily driver you must carefully try to match your torque band to your typical driving style.

I would be surprised if you find a EJ15 Motorsport and race cam is a pleasure to live with when driving around busy urban areas.

Stage 1, 2 and 3 mods for the EJ15

Before we break the best tuning upgrades down into stages of tune, let's list the most effective tuning upgrades for you.

  1. Suspension Upgrades - always improve your cars handling
  2. Brake Upgrades - Even before adding power improve those brakes
  3. Intake - make sure the intake is not restricted, use filters and intake upgrades to improve this
  4. Exhaust - as with 3 ensure there is not restriction in the exhaust, cats are the usual bottleneck
  5. Tunes - remapping, piggyback ECU's and aftermarket ECU's can all make decent gains
  6. Fuelling - when you've increased power you'll need to match this with more fuel
  7. Turbo upgrades - Improving the intake with a large turbo and better flowing intercooler will be the biggest power gain you'll see (but one of the most complex).

This video guide to tuning cars is a great starting point to work from in your project.

Stage 1 EJ15 parts:

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

Tuning tips and articles Engine tuning Transmission tuning Care care Intake & exhaust mods Improve handling Forums

Stage 2 EJ15 parts:

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

Stage 3 EJ15 parts:

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

The EJ15 engines are fantastic to work on and thanks to their popularity there is a growing number of upgrades and tuning parts out there.

ECU mapping should help to release the full potential of all the parts you've done to your EJ15.

You will typically expect to see gains of approximately 20-30% 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 done and the condition of your engine.

Turbo modifications on the EJ15

To get a turbo working on a NASP engine there is a lot involved, from lowering compression ratio to improved fuel supply and mapping, so we have found a great guide to helpavoid the common pitfalls or end up with an unfinished project because you were not told what you were getting into by doing this on the EJ15.

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

If the engine is turbocharged, parts are relatively easy and you will discover turbo engines are built using more solid components.

However you'll find engines have limits

See where you'll find these restrictions and install stronger pistons, crank and engine components to cope with the power.

We've seen tuners spending a a stack of money on turbocharger upgrades on the EJ15 only to suffer the indignity of watching the engine catastrophically fail when it's been finished.

Big capacity turbos commonly experience no power at low rpm, and small turbos spool up quickly but won't have the peak end power band gains.

We are pleased that the world of turbo chargers is always developing and we commonly find variable vane turbo chargers, permitting the vane angle is altered according to speed to lower lag and increase top end bhp.

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

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large bhp and torque gains, although harder to setup. We have this article covering twinchargers if you want to read more.

Tips about fuel supply on the EJ15

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

More power needs more fuel. It is important to be generous with your flow rate on the injectors.

As a rule of thumb add 20% capacity when fitting an injector, which takes into account injector deterioration and affords a bit of spare capacity should the engine need more fuel.

Don't forget that different fuel grades will usually require different settings, a high octane fuel will burn more efficiently than lower octane fuel for example. A car will trim fuel supply to keep within the ideal air fuel mix but at the extreme ends you may need to adjust your injector capacity, or the mapping or you'll get flat spots and potential lean or rich fuel issues..

Recommended EJ15 performance exhaust upgrades

The only time you should look to boost your exhaust system with an upgraded one is if your exhaust is actually creating a restriction in flow.

On most factory exhausts you should find that the flow rate is still ok even on modest power gains, but on a serious tuning project with a big boost in power you will certainly need to get a better flowing exhaust.

Sports exhausts generally help improve air flow through the engine but avoid an exhaust that is too large or you could will reduce the flow rate. Stick to one and a half to two and half inches as a rule of thumb.

Usual exhaust restrictions can be traced to the catalyst and filters installed, so adding a higher flowing high performance alternative will help avoid this restriction.

Decats (NB:catalysts reduce harmful engine emissions) is illegal in most countries and regions.

Faults issues and things to look out for on the EJ15

Like most engines an EJ15, should have few issues if it gets properly serviced and looked after.

We cannot stress enough the need for oil changes with the correct grade of oil on the EJ15, failure to do this will exacerbate engine wear, on a tuned EJ15 this is more important than ever and close attention should be paid to your maintenance schedule.

If you are interested in learning more or getting impartial tuning advice for your EJ15 why not pop over to the forums at TorqueCars where you can chat about EJ15 tuning options and read about others projects who may be planning to do similar modifications on their EJ15.

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