Tuning the Subaru EZ engine

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

Carref prides itself on providing the latest tips and guides to your modification project.

The Subaru EZ engine are popular engines and with carefully picked performance enhancements like remapping, turbo upgrades and camshafts you will noticeably enhance your driving experience.

Here we provide a guide to EZ engine tuning and point out the ultimate mods that work.

We rely on our visitors to pass on tips and tell us about their projects and what worked on their car, and this article is the culmination of the feedback we have received. First let us look at the history and specs of this engine and then consider which tuning modifications work best on it.

History of the Engine

Flat-six, 24-valve, quad-cam engine

EZ30D saw two generations

2000-2003 EZ30D 217 hp @6000 rpm 213 lbft @4400 rpm

• 2000–2004 Subaru Outback H6
• 2002-2003 Subaru Legacy GT30
• 2000–2003 Subaru Legacy Lancaster 6
• 2002-2003 Subaru Legacy RS30

2003-2007 EZ30D  242 hp @6600 rpm 219 lbft @4200 rpm

• 2003–2009 Subaru Legacy 3.0R
• 2005–2009 Subaru Outback 3.0R
• 2006–2007 Tribeca

EZ36D 256 hp @6000 rpm 258 lbft @4400 rpm

• 2010-2019 Subaru Legacy
• 2010-2019 Subaru Outback
• 2008-2014 Subaru Tribeca

Tuning the Subaru EZ engine and best EZ engine performance parts.

What are the most effective EZ engine tuning mods

Just because particular modifications are appear in lots of EZ engine projects it doesn't mean its worth having, we will greatest modifications that will give your EZ engine the biggest power gain return for your cash.

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

Fast road cams usually raise the bhp across the rpm band, you might lose a little bottom end bhp but high end rpm power will be higher.

Motorsport cams, raise the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

A Competition cam won't do well if on the daily commute.

You should ideally optimize your bhp range to your typical driving style so for a typical daily driver stick with a shorter duration EZ engine cam

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

The ECU mapping and fuelling also will make differences 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.

Modifying to STAGE 1:

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

Modifying to Stage 2:

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

Modifying to Stage 3:

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

ECU mapping should help to to establish the full potential of all the modifications you've done to your EZ engine.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but the outcome usually rely on the modifications you've applied and the condition of your engine.

Pulling air and fuel into each cylinder is the aim to any engine upgrade project.

Intake manifold transmit 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.

Design and flow characteristics of the Plenum can make a noticeable difference to to fuel atomisation and engine efficiency on the EZ engine.

We often see intake headers are crying out for aftermarket tuning parts, although a few manufacturers provide decently flowing intake headers.

Big valve conversions on the EZ engine, carrying out port work and head flowing will also boost performance, & more importantly will give you an improved performance increase on other upgrades.

Which turbo upgrades are best?

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 EZ engine

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 your car is fitted with a turbocharger tuning mods are giving better power gains and we find turbocharged engines already contain strengthened components.

There are practical limits for every engine, with some being over specified and some only just able to handle stock power

We recommend you find these restrictions and fit stronger pistons, crank and engine components to utilize the power.

It's not unheard of people spending a lots of money on turbocharger upgrades on the EZ engine only to suffer the humiliation of seeing the whole thing go up in smoke just after it's first rolling road session.

Big upgraded turbochargers tend to experience no power at low rpm, and small turbochargers spool up much more quickly but do not have the peak end power band gains.

Thanks to progress the choice of turbo chargers is always increasing and we now see variable vane turbo chargers, where the vane profile is altered according to speed to lower lag and increase top end performance.

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

It is common that there's a limit in the air flow sensor MAP/MAF/AFM on the EZ engine when considerably more air is being drawn into the engine.

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

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

Fuelling

You will need to ensure that the engine is not starved of fuel so will need to look at the fuelling when you start going beyond 20% of a torque increase.Most tuners we speak with say to be generous with your injectors flow rate.

The rule of thumb is to add 20% capacity when buying an injector, this takes into account injector deterioration and gives a little 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.

Choosing the right performance exhaust

One of the most common mistakes and problems we see in tuning projects is usually down to the exhaust, or rather a poorly chosen exhaust for your engine.

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

On most factory exhausts you should find that your flow rate is good even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Note that with the widest exhaust you can find you'll 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.

Common exhaust restrictions are in the emissions filters installed, so adding a higher flowing race alternative will help avoid this restriction.

Weak spots, Issues & problem areas on the EZ engine

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

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

For more information on Tuning your EZ engine engine please join us in our friendly forum where you can discuss tuning options in more detail with our EZ engine owners. It would also be worth reading our unbiased 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 upgrades work best for them on each model of car. Comments are used to improve the accuracy of these EZ engine articles which are continually updated.

This article was written by Waynne Smith on TorqueCars, and I appreciate your feedback and suggestions. This entry was filed under Subaru. You can leave a response below or join TorqueCars forum to discuss this article and car modification in detail with our members.

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