MENUSubaru EJ257 Tuning
"All you need to know about performance parts and tuning the Subaru EJ257 engine!"
We were asked for more information on tuning and building a modified EJ257 and particularly which turbo upgrades work best, so this feature has been assembled which covers our go to parts for this engine and what we feel are the greatest value parts you can do.
This is one of my favorite engines at the moment, and you can't beat the lovely boxer burble you get, there is no other engine around that sounds as good as a well setup EJ257.
The Subaru EJ257 offer good returns when tuned and with the best motorsport upgrades like a remap, turbo improvements and camshafts you will definitely maximize your driving pleasure.
TorqueCars will review and look at EJ257 tuning and point out the optimum modifications for your car.
History 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.
Best EJ257 parts
Just because particular tuning parts are appear in lots of EJ257 projects it doesn't mean you should fit it, we shall focus on the optimum tuning parts that will give your EJ257 the best power gain for you money.
Getting a fast road cam will come into their own at higher RPM power which makes it a best mod for NASP and turbo petrol engines, but not so much on diesels. Most cars will see top end power hikes through performance camshafts on most engines
So altering your EJ257 camshaft will make a difference to the engine engines power. Choosing a higher performance camshaft profile raises the engines torque curve accordingly.
Fast road cams commonly bump the power throughout the rev band, you may lose a little low end bhp but high end rpm power will improve.
Competition cams, bump 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 daily driver one must carefully try to match your torque band to your cars usage.
You'll never think that a EJ257 Motorsport and race cam is a pleasure to live with when driving in heavy traffic. This is because a competition cam causes a very lumpy idle, and makes the car more prone to stall or jerk along in stop start traffic, sadly though many ignore this and end up ruining a perfectly good car and having to revert back to a fast road, or OEM cam profile.
Some EJ257 engines respond better to extreme camshaft durations so set your engine up on a rolling road.
The engine timing and fuel pump and injectors also will say much on the bhp gains you'll hit.
A longer valve duration 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.
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Best Engine Mods for your car
- Engine Tunes - engine tuning/remapping provides the most advantage in terms of cost savings, aftermarket ECUs, and piggyback ECUs are all alternatives.
- Fast road cams are one of the most significant mechanical changes, but they must be installed by someone who knows what they're doing and they are not always easy to source but you might find a local firm to regrind a stock camshaft.
- Intake and Exhaust - Note that on their own these mods will NOT ADD POWER in most cases, but they can help enhance power after other mods by removing the restriction.
- Upgrades to turbochargers and superchargers - forced induction is the most efficient approach to increase air supply, allowing you to burn more fuel and make more power. It is one of the most costly upgrades but provides the best gains.
- Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.
- 58 PSI 340cc/min 200hp
- 58 PSI 511cc/min 300hp
- 58 PSI 682cc/min 400hp
- 58 PSI 1022cc/min 600hp
- 58 PSI 285cc/min 200hp
- 58 PSI 426cc/min 300hp
- 58 PSI 568cc/min 400hp
- 58 PSI 853cc/min 600hp
- 58 PSI 312cc/min 200hp
- 58 PSI 468cc/min 300hp
- 58 PSI 625cc/min 400hp
- 58 PSI 937cc/min 600hp
Typical stage 1 mods often include:
Sports exhaust header/manifold, Remapped ECU, Panel air filters, Intake manifolds, Fast road camshaft, drilled & smoothed airbox.
Typical stage 2 mods often include:
Sports catalyst & performance exhaust, Ported and polished head, high flow fuel injectors, Fast road cam, induction kit, fuel pump upgrades.
Typical stage 3 mods often include:
Adding or Upgrading forced induction (turbo/supercharger), Crank and Piston upgrades to alter compression, Competition cam, Engine balancing & blueprinting, Internal engine upgrades (head flowing porting/bigger valves), Twin charging conversions.
Remaps allows a tuner to release the full potential of all the parts you've done to your EJ257.
(Sometimes flashing the ECU is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it setup properly.) It will usually give around 30% more power on turbocharged vehicles, but your mileage usually vary depending on the parts you've done and the condition of your engine.
We've seen stage 1 mods and a tune/remap raise power to around 320bhp fairly readily, better exhaust and intake will give another 50bhp if mapped correctly and fuelling is sorted.
Forcing fuel and air into your EJ257 is the main goal to any performance tuning project.
Intake manifold carries the air from the air cleaner and allow it to be drawn into the engine cylinders with fuel for the squish phase.
Design and rate of flow of the Intake manifold can make a big improvement to fuel mixing and power on the EJ257.
It's not uncommon that manifolds are needing aftermarket tuning parts, although some car makers provide reasonably well designed headers.
Increasing the EJ257 valve size, doing some port matching and head flowing will also improve torque, and significantly will afford you an improved torque increase on other modifications.
Changing the pistons and crank can increase cylinder capacity and give you a little more headroom in your tuning project.
EJ257 Turbo upgrades
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.
When an engine is turbocharged, parts are simpler to install and we find turbo engines are built using stronger components. The stock turbo is very well designed, the VF43 can flow to around 370bhp so is a logical upgrade point if you want more power.
The angle of the OEM turbo is an issue if you want to install a larger turbo. Just rotating the mount 45 degrees using a rotated turbo kit will widen the choice allowing full size turbos to be fitted.
There are common areas of failure for every engine, with some being very over engineered and some just sufficiently able to handle stock power. Research these limits and fit more solid crank and pistons to survive the power. On 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.
There are many people spending a lot of money on turbocharger upgrades on the EJ257 only to have the EJ257 throw a rod on it's first outing after it's been enthusiastically driven.
Large capacity turbochargers will usually suffer a bottom end lag, and smaller turbochargers spool up quickly but don't have the peak rpm engines power gains.
In recent times the market of turbo chargers is always moving on and we are seeing variable vane turbo chargers, permitting the vane profile is altered according to speed to lower lag and increase top end bhp and torque.
Forced performance reds are highly commended by Subaru owners, but we've seen impressive power figures from a GT35R or GT40, the ball bearings aid spool up.
Twin scroll turbo chargers divert the exhaust flow into two channels and flow these at differently angled vanes in the turbo charger. They also improve the scavenging effect of the engine and with equal length exhaust they make a lot of sense on the EJ257 for a fast road application.
It is common that there's a limit in the air flow sensor AFM/MAP on the EJ257 when loads more air is being drawn into the engine.
We note 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped torque at a much lower level.
A front mounted intercooler is much more efficient than a top mounted one, and the aftermarket ones resist heat soak for much logner.
Fuelling
When you lift the performance you will need to pay attention to the fuelling.
More performance needs more fuel. 
We would recommend you to be generous with your injector capacity.
The rule of thumb is to add 20% to the flow rate when buying an injector, which 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. The injectors also need a good supply of fuel and most EJ257 owners opt for a walbro 255 fuel pump or similar.
All the following flywheel power targets will assume an injector duty cycle of 80% and a base of 58psi of fuel pressure at idle.
4 Cylinder turbocharged engines
4 Cylinder NA (naturally aspirated) engines
4 Cylinder supercharged engines
EJ257 Performance Exhausts
You should look to replace your exhaust if your current exhaust is actually creating a restriction.
On most factory exhausts you'll find your flow rate is still ok even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.
Don't go with the biggest exhaust you can source you'll reduce the exhaust flow rate - the best exhausts for power gains are usually between 2.75 to 3 inches. It is the shape and material more than the bore size.
Wrap the manifold to keep underbonnet temps down and use equal length pipes, due to the layout of the engine many exhaust header/manifolds vary runner lengths.
Common exhaust restrictions are traced to the filters installed, so adding a freer flowing race aftermarket unit will improve air flow, and rather than doing an illegal decat, will keep the car road legal.
Weak spots, Issues & problem areas on the EJ257
The EJ257 engines are generally reliable and solid units, as long as you follow the manufacturers service schedules, and use a good quality oil to ensure longevity. Few problems should happen as long as they are regularly serviced and maintained.
Regular oil changes are vital on the EJ257, especially when tuned and will help extend the life and reliability of the engine.
If you want to know more, or just get some friendly advice on Tuning your EJ257 engine please join us in our car forums where you can discussEJ257 tuning options in more detail with our EJ257 owners. It would also be worth reading our unbiased Subaru tuning articles to get insights into each modification and how effective they will be.
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One Response to “EJ257 Tuning”
Not really a comment as much as a question. I am running a JDM ej257 with twinscroll turbo in my 04 forester xt with american ECU. I’m having an issue with unstable 02 sensor reading. My tuner recommend moving the front sensor from the downpipe to the header. I did that but the A/F corrections are still all over the scale. My tuner says it will never run smooth because I’m running a twinscroll on a single scroll ECU. Any ideas on how I can smooth these A/F corrections out with the current hardware I am running or by adding/changing hardware?