Engineering Explained: How Subaru Made the S209 Engine That Much Better
This powerplant is ancient, but it’s looking damn tasty in the S209!by Jonathan Lopez, on
Import fans with a fondness for rally-bred speed got quite the treat this week, as Subaru revealed its fastest, best handling, hardest braking STI ever - the S209. This thing is purpose-built from the factory for maximum performance thrills and comes with a long list of upgrades that includes new stuff in the power department. Engineering Explained goes under the hood scoop to figure out exactly what makes this boxer rumble.
Flat-Four For The Win
For those of you who may be unfamiliar, the S209 is powered by the EJ257, a turbocharged 2.5-liter flat-four that’s been around since the first STI first hit U.S. shores back in 2003.
That makes it practically ancient, but Subaru’s boffins have wielded their magic to keep it on pace with the modern competition.
As the above video explains, the engine now comes with a new conical air filter and induction box, followed by a bigger spec for the turbo and an easy-flow exhaust system.
Boost pressure is increased to 18 psi over the standard model’s 16.2 psi, with forged pistons and forged connecting rods in place to handle it without issue. Up top, the intercooler is cooled by a water spray system.
Compared to the standard STI, the S209 offers 341 horsepower, an increase of 31 horses. Torque is increased by 10 percent in the mid-range compared to the 290 pound-feet of the standard model, although specifics are still forthcoming with regard to peak rpm and twist numbers.
Engineering Explained proceeds to go into detail on the intercooler spray system and why the top-mount chiller set-up makes sense on the EJ25, while also answering a few questions on how it all plays out in the real world with regards to water quality and freezing ambient temperatures.
It’s pretty interesting stuff if you’re into the nitty-gritty details of a turbocharged engine, or you just love the Subaru WRX STI S209.
As a reminder, the 2020 Subaru WRX STI S209 also comes with a number of chassis, suspension, and aero upgrades to match the extra ponies, including wider wheels and tires, flared fenders, a carbon fiber rear wing, stiffer springs, new Bilstein dampers, draw stiffners, and plus-sized Brembo brakes.
Pricing is so far unannounced, but the 2020 Subaru WRX STI S209 will likely slot above the $50,000 mark. Production is limited to 200 units total. Sales will commence later this year.
Read our full review on the 2017 Subaru S208 WRX STI Limited Edition.
Read our driven review on the2018 Subaru WRX STI.