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The next-gen Subaru WRX and WRX STI will allegedly both use versions of the brand's 2.4-liter turbocharged flat-four engine, according to Japanese site Car Sensor. Three turbocharged powerplants will motivate 80 percent of the automaker's lineup by 2021.

The FA24 2.4-liter turbo flat-four is already familiar from models like the Ascent, Legacy, and Outback. It produces 260 horsepower (194 kilowatts) and 277 pound-feet of torque and 277 pound-feet (376 Newton-meters) of torque in all three of these models. The new WRX and WRX STI reportedly use a high-output version of this mill.

Gallery: 2017 Subaru Viziv Performance concept

A rumor suggests this high-output FA24 could make 400 hp (298 kW) and 361 lb-ft (490 Nm) of torque. To handle the extra power, there would be parts like stronger internals, different valves, and more boost.

There are allegedly three reasons for switching to the FA24 for the next-gen WRX and STI. First, it's more efficient than the earlier engines. Also, Subie is less concerned with international motorsports where the rules generally favor a 2.0-liter displacement. Finally, folks outside of Japan are used to a WRX STI with a 2.5-liter powerplant, and these customers are accustomed to the drivability of a larger displacement engine.

A six-speed manual would remain available for them. According to Car Sensor, the existing CVT can only handle up to 295 lb-ft (400 Nm). It's not clear how Subie intends to handle this issue.

A rumor suggests that Toyota is offering some input into the new WRX and STI, including using advanced all-wheel-drive tech. This system might have something in common with the Yaris WRC's system.

In addition, a new 1.5-liter turbocharged flat-four will replace models with the current naturally-aspirated boxer engine, so it'll likely be in future versions of the Impreza and Crosstrek. Plus, there will be a 1.8-liter turbocharged flat-four that will power the next Levorg, according to Car Sensor.

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