Watch the reveal of the Subaru Levorg Prototype at the Tokyo motor show.

The next-generation Subaru WRX STI will get a healthy dollop of power, according to sources close to the manufacturer.

The engine of choice is the increasingly familiar 2.4-litre turbocharged flat four, currently employed in the North American Ascent, Outback and Legacy models. In those applications, it makes 194kW/376Nm, nothing to sniff at but not quite enough for the iconic STI badge.

According to Forbes, which cites "sources close to the Japanese automaker," Subaru's engineers will rework the engine to push outputs up to 298kW/490Nm. That's a hefty increase from the current STI, which offers 221kW and 407Nm of torque.

Supplied The next generation WRX and WRX STI could take styling inspiration from the 2017 Viziv Performance Concept.

There aren't any transmission details, leading to speculation that Subaru is considering ditching the manual, but an all-wheel drive system is all but guaranteed. A move to the Subaru Global Platform is also expected.

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Subaru has high expectations for the new engine, as it is allegedly benchmarking it against the new Mercedes-AMG M139 2.0-litre turbocharged four-pot. At its best, that engine makes 310kW/500Nm.

Supplied Power will be allegedly nudging 300kW and will be sent to all four wheels, as is Subaru tradition.

Interestingly, the 2.4-litre engine has been linked to the second generation BRZ/GR86. We wouldn't expect those models to be pushing the same power as the STI but it could mean the upcoming coupes could be tuned to break the 300kW barrier without much difficulty.

That will ultimately depend on how many oily bits the STI engineers change.

It may also power a version of the standard WRX, making a reported 200kW/400Nm.

Supplied Subaru might not offer a manual transmission for new WRX/STI siblings, meaning the current generation will be the last to offer three pedals.

As for the rest of the upcoming STI, it will likely take styling cues form the 2017 Viziv Performance Concept. The overall shape will then be familiar but with more pronounced lines and a coupe-like silhouette.

The Viziv has a longer wheelbase than the current WRX but shorter overhangs, meaning length won't increase by much. Width will probably increase as well.

For now, Subaru NZ is still selling the current WRX and WRX STI. The former starts at $48,990 and the latter $59,990. Both offer a manual transmission and they could well be the last WRX and STI models to do so. Future classics, then?