How much horsepower will the top-spec M40i have?

We already know BMW's M division won't get its hands on the upcoming Z4. The top-spec model will wear the M40i emblem, and a recent report suggests it could offer two different power outputs.BMW is testing two variants of the M40i, according to enthusiast website BMW Blog. The first uses a 3.0-liter straight-six called B58M1 internally and tuned to produce 335 horsepower; the second uses another 3.0-liter straight-six named B5801 rated at 385 horsepower.

There are several ways to explain the power difference between the two six-cylinder engines. As BMW Blog notes, the one with the higher output could be for power-hungry markets like the United States, while the one with the lower output could be for Europe, where tight emissions regulations compounded with expensive gasoline and high, power-based registration taxes could make the 385-horsepower model a tough sell.

Although pure speculation, the 385-horsepower engine could be part of a Competition Package that will also bring a tighter suspension, bigger brakes, and a few components made out of carbon fiber. If that's the case, that means the base Z4 M40i will get a 335-horsepower six.

We'll learn more about the 2018 BMW Z4 in the coming months. It's expected to look a lot like the Concept Z4 (pictured) when it makes its debut next year at the Geneva Auto Show.

Photos by Ronan Glon.