Modding and performance tuning parts for the Subaru EJ18 engine!

The Lowdown on "EJ18 Modifications"

How to modify and upgrade the Subaru EJ18

"Comprehensive guide to tuning the Subaru EJ18 engine!"

TorqueCars often are getting emails requesting information on how to improve the EJ18 from people wanting to know what are the things tuners recommend when it comes to EJ18 upgrades. So let us look into Subaru EJ18 modifications and outline the best modifications on this great engine and point out some potential pitfalls along the way.

Now we will consider EJ18 tuning and provide tips on the best modifications. Subaru EJ18 really good project engines and with carefully chosen tuning tuning mods like a remap, turbo kits and camshafts you will definitely enhance your driving experience.

Just because particular mods are are common on EJ18 it doesn't mean you should fit it, instead we will focus on the top mods that will give your EJ18 the best value for money to power increase.

Without us subscribing to the mentality of 'if it's shiny and makes more noise it must be good' you seem to get in many tuning magazines and on car forums'.

EJ18 induction kits

Improving air intake on the EJ18

You need air matched to fuel for an engine to work. If there is insufficient fuel then it will run lean, if there is little flow of air it runs rich losing power . We'll pick up on fuelling later in this article but for now we shall look at air supply.

So Forcing air into your EJ18 is the main goal to any car tuning task.

It is common that there's a limit in the air flow sensor AFM/MAP on the EJ18 when considerably 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 sapped performance at a much lower level.

Engine intake manifolds carry the air during the suck phase from the filter and allow it to be pulled into the engine cylinders with fuel for the squish phase.

The bore size, shape and flow rate of the Headers can make a big effect on to fuel atomisation on the EJ18.

On popular production engines air intake manifolds are improved through aftermarket tuning parts, although some makers provide reasonably good air intake manifolds.

Adding a EJ18 larger valve kit, doing some EJ18 port enlargement and head flowing will also boost torque, and as an added benefit will allow you to get raising the torque increase on other mods.

EJ18 performance cam tips.

Some EJ18 engines respond better to more aggressive cam durations than others.

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

Extending exhaust or intake 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.

Altering your EJ18 cam will make a dramatic difference to the engine torque. Choosing a higher performance cam profile raises the torque accordingly.

NB: Fast road cams commonly push up the performance over the rev band, you could sacrifice a little low end bhp but the higher rpm power will be lifted.

Competition cams, push up the higher rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

For a road car you need to optimize your torque band to your typical driving style.

I'd never find a EJ18 Race cam is a pleasure to live with when driving in heavy traffic.

Stage 1, 2 and 3 mods for the EJ18

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 EJ18 parts:

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

Stage 2 EJ18 parts:

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

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

Stage 3 EJ18 parts:

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

Plan your options and then acquire your parts and set yourself a power target to avoid costly mistakes.

A remap will help release the full potential of all the mods you've done to your EJ18.

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 results may depend much on the mods you've applied and the condition of your engine.

Turbo modifications on the EJ18

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 EJ18.

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.

When an engine is turbo charged parts are more reliable and we find turbo charged engines are made using uprated components.

However every engines have weakspots

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

There are many car owners spending a lots of money on turbo charger upgrades on the EJ18 only to see the car explode soon after it's completed.

Larger upgraded turbos commonly experience a bottom end lag, and smaller turbos spool up really quickly but won't have the peak end bhp gains.

Thanks to progress the choice of turbos is always evolving and we commonly find variable vane turbos, allowing the vane angle is altered according to speed to lower lag and increase top end power.

Twin scroll turbos divert the exhaust flow into two channels and push these at differently designed vanes in the turbocharger. They also help the scavenging effect of the engine.

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large torque gains, although more difficult to install. We have this article on twincharging if you want to read more.

Tips about fuel supply on the EJ18

When you improve the bhp and torque you will need to pay attention to to the fuelling.

More bhp and torque needs more fuel. Experienced mechanics will tell you to be generous with your injectors flow rate.

The accepted safe increase is to add 15% capacity when specifying an injector, this accounts for injector deterioration and allows some spare capacity should the engine require 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 EJ18 performance exhaust upgrades

The only time you should look to improve your exhaust system with an upgraded one is if the current exhaust is actually creating a flow problem.

On most factory exhausts you'll find the flow rate is still fine 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.

Note that with the largest exhaust you can find you'll slow up the exhaust flow rate - the best for power gains are usually between one and a half to two and half inches. Your exhaust design, the bend angles and construction are what have more effect on flow rates than your pipe width to a certain extent. So the exhaust design is a big factor.

Typically exhaust restrictions can be traced to the catalyst installed, so adding a higher flowing race alternative will help avoid this restriction.

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

Faults issues and things to look out for on the EJ18

Like most engines an EJ18, 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 EJ18, failure to do this will exacerbate engine wear, on a tuned EJ18 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 EJ18 why not pop over to the forums at TorqueCars where you can chat about EJ18 tuning options and read about others projects who may be planning to do similar modifications on their EJ18.

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