The 475-horsepower straight-six will later power the M3/M4 duo.

The first-ever BMW X3M will inaugurate a brand-new straight-six engine, according to a recent report.

Called S58 internally, the six-cylinder will be an evolution of the S55 unit currently found under the hood of the M3/M4 duo. Without citing sources, enthusiast website BMW Blog reports the modifications made to the engine will bump its power output to about 475 horsepower.

To put that figure into perspective, the twin-turbocharged straight-six in the current M3 makes 425 horsepower in its most basic version. Equally interesting is the fact that, 20 years ago, an E39-generation M5 offered 400 horsepower.

The S68 will retain the S55's 3.0-liter displacement and twin turbochargers. There's no word on whether it's being developed with electrification in mind. It might be, because BMW's M division has recently confirmed it's looking into adding an electric motor and a battery pack to its cars.

We expect to see the first-ever BMW X3M before the end of 2018; a public debut at the Geneva Auto Show in March of next year looks likely. The model will go on sale in time for the 2019 model year.

The X4M that will make its debut shortly after will also receive the German firm's newest six-cylinder engine. After that, the engine will power the next M3 and M4 which are tentatively scheduled to arrive by the end of the decade.

Photo by Ronan Glon.