Tuning the Subaru EZ engine

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

The Subaru EZ are popular tuning projects and with carefully picked motorsport upgrades like remapping, turbo kits and camshafts you will noticeably maximise your driving enjoyment.

Here we review EZ tuning and highlight the premier modifications for your car.

When talking about the best best for your EZ engine, we are going to focus on the mods that give the biggest return for your cash.

The cam profile plays a big part in the engines power output so cam upgrades make quite a large difference. The intake and exhaust durations will alter depending on the chosen cam profile, so large torque gains are on offer for cam upgrades.

NB: Fast road camshafts usually raise the power over the rev range, you could drop a little low down bhp but the higher rpm power will improve.

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

On a typical daily driver must carefully try to optimize your engines power to your usage of the car.

You will never find a EZ Race camshaft is a pleasure to live with when driving around busy urban areas.

Different EZ engines respond better to more or less aggressive cam durations so set your engine up on a rolling road.

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

Extending exhaust or intake 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.

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Guide to the Best Tuning Mods & Upgrades

  1. Mods that Remove a Restriction

    If the intake or exhaust are restricted in any way this will have an impact on your cars performance, so use an induction kit/filter upgrade and better flowing exhaust whenever your tuning creates a flow restriction.

  2. Mods that Improve Handling

    Braking, Suspension and general alignment of the suspension components is vital for any tuning project even before you start increasing power.

  3. Fit Stronger Parts

    Tuned cars will show up weaknesses, typically in the turbochargers, clutch and internal engine components. Whilst most engines can cope with mild tuning mods, TorqueCars recommend that you upgrade the internal components before these weak spots manifest themselves.

  4. ECU Tunes & Remapping

    While some cars can be easily remapped, others may require piggyback ECU's or aftermarket ECU's but this is the most vital step of your tuning project as it fully releases the power from all of your mods and upgrades. Expect 10-20% on NASP engines and 30-40% on turbocharged units.

  5. More Power Needs More Fuel & Air

    Every tuning project will aim to increase the air supply, but fuel supply is just as vital and will need to match the air the engine can utilise. Fuel to Air ratio is vital so upgrade the fuel pump & injectors. Also you can look to perform head mods (flowing and porting), bigger valves, fast road cams and forced induction upgrades to improve fuel.

Stages of Tune

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

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

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

Carefully think through your options and then buy your upgrades and set yourself a power target to avoid wasting your time and money.

Mapping will help fully realize the full potential of all the parts you've fitted to your EZ.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but your mileage usually depend much on the parts you've fitted and the condition of your engine.

Getting air and fuel into your EZ is the main goal to any car tuning job.

Headers flow the air from the intake filter and allow it to be drawn into the engine cylinders.

The bore size, shape and flow rate of the Intake manifold can make a substantial effect on to fuel atomisation and engine efficiency on the EZ.

It's not uncommon that air intake manifolds are begging for aftermarket tuning parts, although a few makers provide reasonably good air intake manifolds.

Fitting big valve kits, doing a bit of EZ port enlargement and head flowing will also lift performance, and importantly will permit a greater performance increase on other upgrades.

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 EZ

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

When an engine has a turbocharger upgrades are giving better power gains and most turbo charged engines are built using better components.

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

Discover these limits and fit forged components to survive the power.

It's not unheard of mechanics spending a a stack of money on turbo charger upgrades on the EZ only to see the whole thing throw a rod on it's first outing after it's been completed.

Big turbo units often experience a bottom end lag, and smaller turbo units spool up much more quickly but do not have the top end power band gains.

We are pleased that the selection of turbos is always improving and we now see variable vane turbos, where the vane angle is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbos divert the exhaust gases into 2 channels and push these at differently designed vanes in the turbo. They also improve the scavenging effect of the engine.

You'll commonly see there is a limit in the air flow sensor (AFM/MAF/MAP) on the EZ when loads 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 sapped performance at a much lower level.

Adding a supercharger or additional turbo will make large bhp and torque gains, although more difficult to get working. We have this in depth look at twinchargers if you want to read more.

Fuelling upgrades and mods

Don't forget to uprate the fuel system when you are increasing the bhp - it makes the car more thirsty. We strongly recommend you to be generous with your flow rate on the injectors.

The rule of thumb is to add 20% to the flow rate when specifying an injector, this allows for injector deterioration and allows some 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.

Exhaust upgrades and mods

Only look to increase your exhaust if the current exhaust is actually causing a restriction in flow.

On most factory exhausts you'll see the flow rate is still fine even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Do not go with the biggest exhaust you can find you'll reduce the exhaust flow rate - the best 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 typically happen through the catalyst and or DPF filters which manufacturers fit, especially as they start to get worn and carbon builds up, so adding a higher flowing high performance alternative will help avoid this restriction.

Weak spots, Issues & common problem areas on the EZ

The EZ engine engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the EZ engine, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

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

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.

We need your help improving this article, so please send us your feedback in the comments box below and pass on any tips, points or facts we have wrong or have not covered.

We really like hearing from our readers, and hearing about which upgrades were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our EZ engine guides and tips are kept up to date.

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