Though neither are in production today, Subaru’s 2.5 liter EJ255 vs EJ257 motors are still some of the most sought out and recognizable in JDM history. Of the two, the EJ257 offers better performance and potential for modding, but both are outstanding motors. Subaru primarily used the engines inside the high performance Legacy GT and Impreza WRX (EJ255), as well as in the Impreza WRX STI (EJ257).
Both engines have hard earned reputations for being very powerful and well designed, and they are pretty reliable when taken care of, too. Let’s take a few minutes to look back at two of the most iconic motors in Subaru history, the EJ255 vs EJ257.
Subaru EJ255 vs EJ257 History
Subaru first brought the EJ255 and EJ257 engines to the United States for the 2004 model year. They stuck the EJ257 inside the inaugural Impreza WRX STI, where it made 300 horsepower and 300 lb-ft of torque. As for the less potent EJ255, Subaru gave that to the Baja Turbo and Forester XT, and later the Outback XT and Legacy GT. Compared to the STI, these vehicles made just 210 horsepower and 235 lb-ft of torque. Still, they were pretty sporty for their time and offered much better performance than the base engines.
In 2006, Subaru also put the EJ255 inside the WRX, where it replaced the EJ205 and achieved its most prominence. Depending on the version, year, and model it was inside, the EJ255 made 210-265 horsepower and 226-258 lb-ft of torque. Comparatively, the EJ257 produced 293-310 horsepower and 290-300 lb-ft of torque in the standard models.
The only non-Subaru to ever get either engine was the 2006 Saab 9-2X. Saab used a 230 horsepower and 235 lb-ft of torque version of the EJ255 for their sedan. Subaru created several variants of the EJ257, two of which made it stateside. The first was found in the 2018 WRX STI Type RA, which eventually became the standard STI motor from 2019–2021. Subaru also made another high performance variant for the 2019–2020 WRX STI S209, which made an incredible 341 horsepower and 330 lb-ft of torque.
Subaru kept the EJ255 in production through 2014 inside the Impreza WRX. In 2015, they replaced it with the 2.0 liter FA20DIT. They kept the EJ257 in production longer, through 2021, when they retired it and the STI alike.
Subaru EJ25 Specs
|Engine Family||Subaru EJ||Subaru EJ|
|Displacement||2.5 liters (2,457 cc)||2.5 liters (2,457 cc)|
|Configuration||Flat-Four, Boxer||Flat-Four, Boxer|
|Compression Ratio||– 8.2:1 (Version 1)|
– 8.4:1 (Version 2)
|Bore & Stroke||99.5 mm x 79 mm||99.5 mm x 79 mm|
|Fuel System||Electronic Fuel Injection||Electronic Fuel Injection|
|Valve Train||DOHC, 16-valve||DOHC, 16-valve|
|Horsepower Output||210-265 horsepower||293-341 horsepower|
|Torque Output||226-258 lb-ft||290-330 lb-ft|
EJ255/7 Equipped Vehicles
Subaru’s EJ255 appeared in the following USDM vehicles:
EJ255 Version 1 (210 horsepower, 235 lb-ft of torque)
- 2004–2006 Subaru Baja Turbo
- 2004–2005 Subaru Forester XT
- 2005–2006 Subaru Legacy GT
- 2005–2006 Subaru Outback XT
EJ255 Version 2
- 2006 Saab 9-2X (230 horsepower, 235 lb-ft of torque)
- 2006–2014 Subaru Impreza WRX (224-265 horsepower, 226-244 lb-ft of torque)
- 2006–2013 Subaru Forester XT (224-230 horsepower, 226-235 lb-ft of torque)
- 2007–2012 Subaru Legacy GT (243-265 horsepower, 241-258 lb-ft of torque)
- 2007–2009 Subaru Outback XT (243 horsepower, 241 lb-ft of torque)
Subaru’s EJ257 appeared in the following USDM vehicles:
- 2004–2014 Subaru Impreza WRX STI (293-305 horsepower, 290-300 lb-ft of torque)
- 2015–2021 Subaru WRX STI (305-310 horsepower, 290 lb-ft of torque)
- 2018 Subaru WRX STI Type RA (310 horsepower, 290 lb-ft of torque)
- 2019–2020 Subaru WRX STI S209 (341 horsepower, 330 lb-ft of torque)
Subaru EJ255 & EJ257: Similarities and Differences
Both the EJ255 vs EJ257 engines are very similar to each other. Both are turbocharged, four-cylinder, horizontally opposed, boxer-style engines. They each have 2.5 liters of displacement and use aluminum engine blocks and cylinder heads. The bore and stroke is 99.5 mm x 79 mm, and they both utilize electronic fuel injection. The blocks are “semi-closed deck,” which means they have considerable strength.
Each engine also has a dual overhead camshaft (DOHC) valve train with four valves per cylinder for 16-valves total. Subaru used sodium-filled exhaust valves for temperature control until 2008. Both the EJ255 and EJ257 use Subaru’s proprietary variable valve timing technology known as Active Valve Control System (AVCS).
All versions of the EJ255 have single-AVCS on the intake camshafts. The 2004–2007 EJ257 have single-AVCS on the intake cams, while the 2008+ versions had dual-AVCS on all four-camshafts.
EJ255 vs EJ257: Short Block and Cylinder Head Differences
Subaru released two versions of the EJ255, version 1 and version 2. Of these, the version 1 engine is practically identical to the early EJ257. They both used the same exact AB440-code short block and same camshafts, but they used slightly different heads. The EJ255 heads were the AB650-code, while the STI used AB640/910-code heads, better known as the B25 heads. Besides that, the version 1 EJ255 is basically just an EJ257, and both have 8.2:1 compression.
Starting in 2006, for most models, except the Legacy GT and Outback XT which got it a year later, Subaru replaced the version 1 EJ255 with the version 2. Compared with the version 1, the version 2 EJ255 had a new short block (AB630-code) as well as new heads (AB820-code) known as D25 heads. These heads had a smaller combustion chamber and used a secondary air induction system, which resulted in a slightly higher 8.4:1 compression ratio. Through 2014, the EJ255 version 2 block and heads did not undergo any more significant revisions.
In 2007, Subaru added a secondary air injection system to the EJ257 in the STI. This did not change performance, but necessitated the use of new cylinder heads with the V25 designation. In 2008, Subaru once again changed things, adding AVCS to the exhaust camshafts for the EJ257. This again meant new heads, now with the W25 designation.
These stayed the same until the 2018 Type RA STI, which got new N25 heads that appear to flow even better. In 2019, these became the standard EJ257 heads, which remained in use through 2021. Check out this post from IGotASTI.com that details how the EJ257 has changed over the years.
EJ255 vs EJ257: Turbos
Subaru used several different turbochargers for both the EJ255 and EJ257. For the EJ257 inside the STI, Subaru originally used the IHI VF39 water-cooled turbo running 14.5 PSI of boost. In 2007, they replaced the VF39 with the VF43 that had a stiffer wastegate due to the VF39’s cracking. The following year in 2008, Subaru again replaced the turbo, this time with the VF48 running 14.7 PSI of boost.
For the Type RA EJ257, they upped the boost to 16.2 PSI but kept the same turbo. This changed for the special S209, which used an HKS turbo. Compared with the VF48, the S209 turbo has a 56-mm turbine wheel diameter, a 65-mm compressor wheel, and runs 18.9 PSI of boost.
As for the EJ255, Subaru first used a Mitsubishi TD04-13T which made 11.6-13.5 PSI of boost. In 2008 in the WRX, they switched to the TD04-19T, which made 11.3 PSI of boost. From 2009-on in the WRX, they used the IHI VF52 which made 13.5 PSI of boost. As for the Legacy GT, Outback XT, and Forester XT, Subaru gave them the IHI VF40 and then IHI VF46 turbos.
All Subarus use air-to-air intercoolers that are top-mounted. The EJ257 intercoolers are larger and capable of superior cooling vs the EJ255 units. EJ257 intercoolers also have water sprayers that help to improve cooling and can be activated inside the cabin. However, in 2008 they removed the intercooler sprayer system, and only brought back inside the version for the S209, which uses dual sprayers.
EJ255 & EJ257: Internals
Internally, there are some differences between the EJ255 vs EJ257. Both of them do use cast aluminum pistons, though they are slightly different designs. For the connecting rods, both EJ255 and EJ257 use forged steel rods. The EJ257 rods have bigger end caps and higher strength rod bolts, while the EJ255 rods have different end caps. The EJ257 connecting rods are much stronger.
All versions of the EJ255 and the 2004–2007 EJ257 use untreated forged carbon steel crankshafts. Beginning in 2008, Subaru gave the EJ257 a nitride-treated crankshaft. They also made the rods stronger, though they were still forged steel.
The EJ25’s Reliability
The big question is which is more reliable, the EJ255 vs EJ257? To be fair, both of them are relatively reliable engines — provided they are properly maintained and cared for. There is not a significant difference in reliability between the two engines, and they both suffer from the same basic problems of ringland failure, turbo failure, and rod bearing failure.
Overall, the EJ25 series of engines are very stout and reliable. Many drivers have surpassed 200,000-250,000 miles without issue by just doing regular maintenance. In addition, they have also been shown to be capable of handling some insane amounts of power. Fully built EJ25 engines with forged internals have been known to blow past 1,000 horsepower quite often, showing just how well engineered these engines truly are.
EJ255 vs EJ257 Modding
For many enthusiasts, the most important question of the EJ255 vs EJ257 debate is of course, which is better for performance and modding? While both engines are relatively similar, it’s always been clear from the beginning: The EJ257 is definitely the better motor for performance and modding. From the factory, the difference is already obvious, with the EJ257 making 293-341 horsepower and 290-330 lb-ft of torque, while the EJ255 maxes out at 265 horsepower and 258 lb-ft of torque.
From the factory, the biggest differences are the turbochargers, valve trains, intercoolers, and cylinder heads. The EJ257 has bigger and better intercoolers, higher flowing heads, dual-AVCS (from 2008-on), and larger turbos that run more boost pressure. All of this adds up to much better performance from the factory, and also makes the EJ257 a better power plant to start with.
Both engines respond well to the same basic mods of a downpipe, intake, and ECU tuning. However, the EJ257 will outperform the EJ255 for most builds due to the differences listed above. In addition, while you can upgrade the EJ255 heads, turbo, and intercooler, the dual-AVCS of the EJ257 will still allow it to spool quicker and bring on the boost quicker.
Still, the EJ255 is a very solid motor with which to start building. Like the EJ257, it is capable of making gargantuan horsepower numbers, especially once you upgrade the turbo and intercooler. In addition, you can often find an EJ255 for much cheaper than an EJ257, so you can get similar performance at a better price point. We still recommend the EJ257, but the EJ255 is certainly no slouch.
EJ255 vs EJ257 Summary
The EJ255 vs EJ257 are two of the most legendary Subaru engines in JDM and USDM history. They are both 2.5 liter turbocharged boxer-style engines, and they have enviable performance. Depending on the year and variant, the EJ255 makes 210-265 horsepower and 226-258 lb-ft of torque. In comparison, the more powerful EJ257 makes 293-310 horsepower and 290-300 lb-ft of torque in the standard versions, or 341 horsepower and 330 lb-ft of torque inside the special edition S209.
The main differences between the two engines are the intercoolers, turbochargers, having single or dual-AVCS, and the cylinder heads. Subaru made all of these better on the EJ257 over the EJ255, making the EJ257 a much better engine for performance and modding.
Do you own an EJ255 or EJ257-powered Subaru that you love modding? Let us know in the comments below which engine you think is better!
Subaru EJ255/7 FAQ
The easiest way to identify the difference between the engines is to identify the turbochargers and/or cylinder heads. Each engine uses different markings for the cylinder heads and different turbos which are easy to identify.
Both the EJ255 and EJ257 2.5 liter boxer engines are very reliable and solid motors. Of the two, the EJ257 offers better performance and reliability, though both are great engines.