Subaru’s mighty flagship sports car, the WRX STI, is destined for a major upgrade come 2021. Sources close to the Japanese automaker tell us that the next generation WRX STI will employ an all-new 2.4-liter boxer turbo, called the FA24, pumping out no less than 400 horsepower and 361 lb-ft of torque.

That’s a significant power boost over the current STI which develops 304 hp and 311 lb-ft of torque. The brand’s current Japan-spec WRX STI is powered by a tweaked and tuned version of the Impreza WRX’s 2.0-liter boxer turbo, known affectionately in motoring circles as the EJ20. That engine has been around since 1989, in different iterations since it debuted in the first generation Subaru Legacy. This boxer powerplant was also the engine that competing in, and won three World Rally Championships Manufacturers titles in the mid-90s and three driver’s titles from 1995 to 2003.

According to our source, the U.S.-spec 2.5-liter boxer turbo powered WRX, featuring the EJ25 engine, will remain in service until the next-generation WRX Series is introduced after 2021.

Now, let’s get back to the legendary Japan-spec EJ20. Honed on the rough and tough rally stages around the world, this boxer engine has powered Subaru through 30 years of rally competition and several generations of production cars and gained a legion of fans worldwide in the process.

But all good things must come to an end. Stricter fuel economy and emissions regulations demand a more efficient, cleaner engine and the all-new FA24 boxer turbo has been identified as the powerplant of choice. Subaru fans will immediately realize that the FA24 boxer turbo just happens to be the same engine that powers the current model Ascent SUV. In Ascent spec, the FA24 generates 260 hp.

In next-generation WRX STI spec however, that same FA24 engine will receive significant upgrades to achieve that smoking hot figure of 400 hp. According to our source, the reworked FA24 in STI spec will employ a reinforced crankshaft and pistons, optimized timing balance, fine-tuned valves and intake ports, boost pressure will be tweaked and brake capacity will be enhanced, among other modifications. And married to the brand’s tried and proven symmetrical full-time 4WD system, expect nothing less than class-leading performance and handling.

In creating the new more powerful STI engine, Subaru engineer’s apparently benchmarked the Mercedes-AMG 2.0-liter turbo — as found in the A45 and CLA45 — which pumps out 416 hp and 369 lb-ft of torque. This engine is currently recognized as the most powerful 2.0-liter series-production four-cylinder engine on the planet.

And what about the all important styling of the new STI? Expect the next-gen model to don sheetmetal similar to that in the photograph above, styling that takes significant design hints from the Subaru Viziv Performance Concept first seen at the 2017 Tokyo Motor Show. Characterized by a low, wide body and huge flared fenders, the Viziv concept was one of the Tokyo’s highlights back in 2017.

While hardcore Subarists will be hoping designers don’t alter the body too much from that Viziv concept, they will also be nodding feverishly at a spec sheet that starts with maximum output hovering around 400hp and a price tag expecting to undercut $50,000.

the next generation WRX STI will employ an all-new 2.4-liter boxer turbo, called the FA24, pumping out no less than 400 horsepower and 361 lb-ft of torque. the FA24 boxer turbo just happens to be the same engine that powers the current model Ascent SUV. In Ascent spec, the FA24 generates 260 hp.
In creating the new more powerful STI engine, Subaru engineer’s apparently benchmarked the Mercedes-AMG 2.0-liter turbo — as found in the A45 and CLA45 — which pumps out 416 hp and 369 lb-ft of torque. This engine is currently recognized as the most powerful 2.0-liter series-production four-cylinder engine on the planet.