Other Subie's will get new 1.5- and 1.8-litre turbo engines.

The next-gen Subaru WRX and WRX STI will allegedly both use versions of the brand's 2.4-litre 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-litre turbo flat-four is already familiar from models like the Legacy, and Outback. It produces 260 bhp (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 rumour suggests this high-output FA24 could make 400 bhp (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 favour a 2.0-litre displacement. Finally, folks outside of Japan are used to a WRX STI with a 2.5-litre 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 rumour 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-litre 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-litre turbocharged flat-four that will power the next Levorg, according to Car Sensor.