When Subaru announced it was bringing an S-series WRX STI to the US for the first time, we wondered what engine would power it. A turbocharged boxer-four, obviously, but the Japan-only S208 used a 2.0-liter motor we don't get here in the states. When Subaru pulled the covers off the S209 this week, we learned that the old EJ25 2.5-liter lurked under the hood.
Yes, the same EJ25 that's powered the WRX STI since 2004. In the S209, power rises from 305 hp to 341 thanks to a new turbocharger running higher boost pressure, forged pistons and connecting rods. It's the first time the EJ25 has received a meaningful power boost in 15 years, and we kind of assumed this had to be the end of the line for this motor. It's a good engine, but it's old and surely this would be the final, most special iteration.
Amazingly, that's not the case. At the S209's unveil Detroit Auto Show, we spoke with STI chief engineer Masuo Takatsu to learn a bit more about the car. When we asked if this was the final hurrah for the EJ25, he paused before a Subaru spokesperson interjected to tell us "we still have a few more things we can do with it. [It's] not the final-final."
That's a pretty nice surprise. After all the EJ25 dates back to the mid-1990s in its earliest iteration. It's one of the oldest engines on sale, improbably surviving as emissions standards tighten and increasing fuel economy is paramount.
Most likely, the EJ25 will be officially retired whenever the next generation of WRX STI arrives, though that's likely still a few years out. The new FA24 2.4-liter turbo in the Ascent SUV seems like a likely candidate to power the next STI, as .
But until then, we've got the EJ25, and 341 horsepower might not be its ceiling. It might be an old engine, but it's stout and eminently tunable. We expect Subaru to give it the send-off it deserves.