MENUTuning Feature: Subaru EJ257 Modified
"Comprehensive guide to performance tuning the Subaru EJ257 engine!"
We are frequently getting posts asking how to improve the EJ257 from people wanting to know what are the ultimate EJ257 upgrades. So let us look into Subaru EJ257 parts and outline the best modifications on this great engine and point out some frequent tuning mistakes along the way.
Now we will look into EJ257 tuning and provide tips on the optimum modifications. Subaru EJ257 offer good returns when tuned and with the best tuning upgrades like ECU maps, turbo upgrades and camshafts you will definitely enhance the drivers enjoyment of your car.
The best EJ257 upgrades on an engine are obviously the ones that give the biggest return for your cash.
We won't be swayed by popular EJ257 upgrades, they need to be cost effective.
Significant power increases can be made on engines, and the EJ257 is no exception, from camshaft upgrades. Altering the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the engines power and power output.
NB: Fast road cams tend to increase the power through the rpm range, you could sacrifice a little bottom end power but your high end rpm power will be higher.
Motorsport and race cams, increase the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.
On a road car one, ideally, must carefully try to optimize your torque band to your preferences.
I'd be gobsmaked if you have found a EJ257 Motorsport cam is a pleasure to live with when in heavy traffic.
Some EJ257 engines respond better to less aggressive camshaft durations check your engine on a rolling road.
The ECU mapping and fuel pump and injectors also have a large bearing on the torque gains you'll get.
Longer 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.
EJ257 Best Tuning Mods & Upgrades
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Guide to the best tuning mods & Upgrades
- ECU Map Tuning & Remaps
Some cars may require a piggyback ECU's or aftermarket ECU's to change the OEM map, but remapping is the most vital step of your tuning project to fully maximise your mods. Expect 10-20% on NASP engines and 30-40% on turbocharged units.
- Strengthen Your Engine
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.
- Mods that Remove a Restriction
A restricted intake or exhaust will have an impact on your performance, so use a better flowing air filter/induction kit and better flowing exhaust (sports cats where legal are a good option) whenever your tuning creates a flow restriction. Turbo engines also benefit from intercooler upgrades as these resist heat soak for longer periods of time.
- Mods that Improve Fuelling
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, a fuel pump and injector upgrade are usual mods, but also in many cases the fuel regulator will need improvement.
- Mods to Provide better Airflow
Increasing the air supply is just as essential as improving fuelling, we suggest you look at head mods (flowing and porting, 5 angle valve jobs), fit bigger valves, fast road cams and forced induction upgrades (adding a better flowing turbo) to improve air intake.
Tuning Stages
Stage 1 EJ257 modifications: Intake headers, Drilled & smoothed airbox, Sports exhaust manifold, Panel air filters, Fast road camshaft, Remaps/piggy back ECU.
Stage 2 EJ257 modifications: induction kit, Sports catalyst & performance exhaust, Ported and polished head, high flow fuel injectors, fuel pump upgrades, Fast road cam.
Stage 3 EJ257 modifications: Internal engine upgrades (head flowing porting/bigger valves), Adding or Upgrading forced induction (turbo/supercharger), Crank and Piston upgrades to alter compression, Twin charging conversions, Engine balancing & blueprinting, Competition cam.
A remap will help to establish the full potential of all the tuning mods you've done to your EJ257.
It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but power output often depend much on the tuning mods you've applied and the condition of your engine.
It is the whole point to any engine upgrade job to pull more air and fuel into your EJ257
Intake manifold transmit the air from the air filter and allow it to be drawn into the engine cylinders with fuel for the squish phase.
Design and rate of flow of the Intake headers can make a noticeable effect on to fuel engine efficiency on the EJ257.
We often see plenum chambers are in dire need of performance upgrades, although some makers provide reasonably well designed plenum chambers.
Larger EJ257 valves, carrying out port matching and head flowing will also lift bhp, & importantly will give you an improved bhp increase on other parts.
Turbo upgrades for the EJ257
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 EJ257
The Red from Forced performance are highly commended by Subaru owners, but we've seen impressive power figures from a GT35R or GT40, the ball bearings aid spool up.
The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes superb power gains.
If your car has a turbo already fitted upgrades are more reliable and you will discover turbo charged engines use many forged and stronger components.
However every engines will have power limits and in the EJ257 you'll push around 370bhp on the OEM turbo, the block is good for around 400bhp before pistons and crank need to be replaced with stronger forged components.
See where you'll find these limits and upgrade to more solid crank and pistons to survive the power.
We see many car owners spending a loads of money on turbo upgrades on the EJ257 only to experience the engine block literally blow up on it's first outing after it's been completed.
Bigger upgraded turbochargers tend to suffer no power at low rpm, and smaller turbochargers spool up much more quickly but don't have the peak end engines power gains.
Thanks to new tech the selection of turbochargers is always developing and we now see variable vane turbochargers, permitting the vane angle is altered according to speed to lower lag and increase top end power.
Twin scroll turbochargers divert the exhaust gases into 2 channels and flow these at differently profiled vanes in the turbocharger. They also improve the scavenging effect of the engine.
It is not unusual that there's a restriction in the air flow sensor (AFM/MAF/MAP) on the EJ257 when loads more air is being pulled into the engine.
You'll see that 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped power at a much lower level.
Adding a supercharger or additional turbo will make large power gains, although harder to setup. We have this guide to twinchargers if you want to read more.
Uprating EJ257 fuel injectors
When you boost the bhp you will need to look at to the fuelling.
More bhp needs more fuel. 
It makes sense to over specify your injector capacity.
As a rule of thumb add 20% capacity when specifying an injector, this takes into account injector deterioration and gives a bit of 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.
Best EJ257 performance exhausts
You may need to upgrade your exhaust if the existing exhaust is actually creating a flow problem. Equal length exhuasts are a must on this engine block especially if you are planning a twin scroll turbo.
On most factory exhausts you'll see your 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.
Sports exhausts can usually air flow from the engine but do not go too big or you could reduce the flow rate. Stick to 1.5 to 2.5 inches for best results.
Typically exhaust restrictions are traced to the catalysts installed, so adding a faster flowing sports alternative will help avoid this restriction.
History Power and specs of the EJ257 Engine
EJ257
- US Impreza WRX STi MY 2004-2007
300 bhp (304 PS; 224 kW) at 6000 rpm 407 Nm (300 lbft) at 4000 rpm of torque. - US Impreza WRX STI MY 2008~2018
305 bhp (309 PS; 227 kW) at 6000 rpm 393 Nm (290 lbft) at 4000 rpm of torque. - US WRX STI MY2019–current
310 hp (314 PS; 231 kW) at 6000 rpm 290 lbft (393 Nm) at 4000-5200 rpm of torque - US STI S209 MY 2019
341 hp (346 PS; 254 kW) at 6,400 rpm 330 lbft (450 Nm) at 3,600 rpm of torque. - US Legacy GT/Outback XT MY05-06
250 bhp (253 PS; 186 kW) (New SAE standard) - US Forester XT MY04-05
210 bhp (213 PS; 157 kW) - Asian, European Impreza WRX STi 05-present
280 PS (206 kW; 276 hp) (392 Nm; 289 lbft)
Tuning the Subaru EJ257 and best EJ257 performance parts.
Problems and issues to look out for on the EJ257
The EJ257 engines, if regularly serviced and maintained, are generally very reliable and have few issues. {But if neglected they can cost a small fortune|When neglected they get very expensive to run|They can however be quite expensive if neglected| }
Regular oil changes are vital on the EJ257, particularly when the engine has been modified and is putting down more power than the manufacturer intended.
For more information on Tuning your EJ257 engine please join us in our friendly forum where you can discuss tuning options in more detail with our EJ257 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 to complete and improve this page, so do give us your feedback in the comments box below. We also have a more recent EJ257 tuning article on our US site.
We really like hearing from our readers, and hearing about which modifications were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our EJ257 guides and tips are kept up to date.
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