What makes a great Subaru engine? A great Subaru engine blends power, performance, and reliability in a way that lets the vehicle live up to its fullest potential.
Figure 1: A Subaru FB20 engine. Source: Autoblog.
Subaru engines are known for the top-notch quality of their OEM parts. Years of research and experimentation have gone into Subaru engines, which is why many motorists choose to leave their engines in pure, unadulterated OEM condition. However, for those who do want to do a little tinkering, Subaru engines also make great aftermarket engines thanks to their high reliability and durable parts and performance.
In this post, we’ll look at some of the best and most important engines in Subaru’s storied history. From the original E Series, first introduced in the US way back in the day, to the modern and fully redesigned F series, there have been a ton of great Subaru engines.
We’ll consider the engines from both an OEM and aftermarket point of view.
Sources: Crawford Performance.
1. Subaru FB20D
Figure 2: This 2.0L FB20D from Subaru is the beating heart of the modern Impreza. Source: J-Spec Auto.
The FB series was initially made available as naturally aspirated engines with 2.5-liter and 2.0-liter displacement levels. As the first new generation of engines from Subaru since the EJ series, and the third-generation flat-four engine from the maker, expectations were high when the FB was first announced in 2010.
These engines saw a marked increase in piston stroke and decrease in the bore, which was aimed chiefly at reducing emissions and boosting fuel economy without hindering the performance of the engine. Admittedly, fuel economy had not been one of Subaru’s strong suits up until this point, so these improvements were quite a welcome addition to the FB series.
The new FB engines also allowed for a 28% reduction in friction losses compared to previous models, due chiefly to lighter pistons and connecting rods. This had another, perhaps unintended, effect of increasing the torque output compared to previous generations of Subaru engines. Whether it was their main goal or just a happy accident, we think that extra torque made quite a bit of difference.
Figure 3: This Impreza GK from 2017 is fitted with an FB20D engine. Source: NRMA.
We’ve picked the FB20D as the best of the bunch. Why? Because, unlike the FB20B that preceded it, the FB20D comes with direct injection that provides a noticeable increase in power and efficiency. This engine is used in the fifth generation Impreza sedan and hatchback, and that extra power makes a big difference. This engine features a compression ratio of 12.5:1 when run in the Subaru Impreza. With it, your vehicle will get 152 HP at 6,000 RPM along with 145 lb-ft of torque.
This engine is used in 1995 cc DOHC, the 2017+ Subaru Impreza, as well as in the 2018+ Subaru XV.
2. Subaru EZ36D
Figure 4: The EZ36D engine. Source: Subarucar.net.
The EZ36 engine stands tall as the king of Subaru six-cylinder engines. Compared to the EZ30 flat-six engines that came before, the EZ36 has a larger bore and stroke while incorporating thinner iron cylinder sleeves to accommodate the increased bore. With asymmetric connecting rods, the stroke is increased accordingly. Interestingly, the engine body itself is a bit longer than other Subaru engines, due largely to the modifications to the drive cam.
The EZ36D was used in the Subaru Outback (specifically the 3.6R) from 2010–2019. It achieved 256 HP at 6,000 RMP—certainly an impressive figure—while managing 247 lb-ft of torqu at 4,400 RPM. It is known for being a fair bit more reliable than its EZ30 brethren. It is also a great candidate for a supercharger kit.
The EZ36D, insofar as it experiences engine problems, tends to have the same problems and easy fixes as the EZ30. Click here for more details on common issues.
3. Subaru EJ257
This cute little guy is the Subaru EJ257 engine. It is a 2.5L engine that has its roots in rally racing but makes for an excellent Subaru engine for all kinds of purposes. Originally designed for the USDM 2004 Impreza WRX STI, this engine comes complete with a horizontally opposed 4-cylinder configuration. This allows it to lower the center of gravity.
This engine has a bore and stroke of 3.92” by 3.11”, a peak power output of 300 BHP at 6,000 RPM, and a peak torque of 290 lb-ft at 4,000 RPM.
Figure 6: The 2004–2007 Impreza WRX STI was the proud recipient of the EJ257 engine. Source: Hagerty.
The only car in the US that uses the EJ257 engine is the STI. Other cars using an EJ-series 2.5L engine use the EJ255 instead. Interestingly, there were several cars produced from 2004 to 2006 that technically had EJ257 engines, even if their engines were officially designated as EJ255. Those were:
- Forester XT 2004–2005
- Legacy GT 2005–2006
- Outback XT 2005–2006
This engine has relatively large bores along with relatively short strokes. This is important because it allows the engine to churn out massive torque even in stock form. If that weren’t enough, Subaru’s special AVCS (that’s Active Valve Control System to you) enables variable-valve timing with the intake valves.
The engine also comes with an intake camshaft controlled by the car’s ECU. It can be adjusted up to 35 degrees, allowing the cam timing to be optimized all throughout the RPM range. On top of all these features, the EJ257 is known for being a great aftermarket engine.
Be aware that the EJ257 is known to occasionally have piston-related problems. Broken ring lands have now and then caused blown engines. It also, oddly enough, emits a strange and peculiar exhaust sound that some motorists find irritating. But hey, if you prefer that unique, melodious boxer-engine note, more power to you!
4. Subaru EJ20T WRX STI
Figure 7: An EJ20T engine solidly housed in an Impreza STI. Source: Autos Speed.
These flat-four boxer engines are found primarily in the performance-oriented STI and WRX version of the Impreza. This engine is another great aftermarket choice because it is affordable, available, and can offer up a fair bit of power and torque. Interestingly, whereas the regular Impreza and other members of the Subaru family switched to the “Subaru Global Platform” several years back, the higher-performance WRX and WRX STI models of the Impreza have so far not done so. They’re still based on previous-generation Impreza engine models. However, this does not mean the classic engines are any less impressive.
Note that EJ20T is not actually a code from Subaru. Instead, this term is used by enthusiasts and tinkerers to designate the entire line of turbocharged engines available for the STI or WRX. This practice started with the designation of the USA-spec turbo, often referred to as the “EJ22T.” From there, the habit of referring to all turbocharged engines as a “T” began.
A typical engine will get a power output range of 197 HP at 6,000 RPM. For the GT, power is around 217 HP at 6,400 RPM. These engines can be easily identified by coil on the plug, with 2 M6 bolts per coil and some valve covers with 4CAM 16VALVE labels. Further, horizontal lines above and below the plug holes are also clearly visible. All such engines have the air-to-water intercooler setup and close-deck blocks that are equipped with piston oil ejectors.
We spoke to the experts at Crawford Performance about their Subaru engine options for WRX and STI owners. They explained that they offer engines in 4 levels, from “OEM short blocks for people who just want to replace stock blocks, all the way to level 4, which is a crazy race level that will get 600 to 700 HP.”
Figure 8: A Subaru WRX STI from 2017. Source: Guide Auto.
Level 3 includes the Subaru S3 engines. Crawford’s S3 “basically has Crawford-designed JE pistons and rods, along with a brand-new stock block. This will run about $3,500.” However, they made sure to add that “you’d also need a short-block install kit, since you’re going to have to replace the oil and other things. That’ll run another $800.”
As they explained, “it all boils down to whether or not you have a good tuner. If you’re going way above the OEM stock power range, make sure you have a good tuner.” Otherwise, the engine will experience serious problems and have a shortened lifespan.
“Other than your purchase of the block and installation, the tune is the most important factor,” the experts and Crawford emphasized. Finally, “make sure you have an air-oil separator, it’ll extend the life of any engine you have.”