We've been eager to find out more about the upcoming 2018 BMW Z4 M40i, codenamed G29, ever since the ravishing Roadster Concept was revealed. According to BMW Blog, the range-topping roadster could come in two flavors to compensate for the lack of a full fat M-badged version. Sources suggest that the roadster will be powered by a turbocharged 3.0-liter engine likely to be sourced from the 340i. For the base model, the Z4 M40i will allegedly utilize the "B58M1" specification of the engine delivering 335 horsepower.

The more powerful "B5801" variant will utilize the same engine, but crank the power up to 385 hp and benefit from a slight increase in torque. BMWBlog speculates that there could be two factors that influenced BMW's decision to develop two different specifications for the Z4 M40i. Firstly, this could be BMW's method of adhering to different emissions standards around the world. Europe has much stricter emissions regulations compared to the US, for example. So it's possible that the less powerful variant is being developed for the European market, whereas the US would get the 385-hp convertible.

Alternatively, BMW could be reserving the higher spec for a hotter Z4, possibly as an optional Competition Package. If so, the Z4 M40i would benefit from other tweaks such as a more aggressive exhaust note, enhanced wheels and unique wheels in-line with Competition Packages released for past BMWs. Of course, the M40i won't be the only Z4 available. A base Z4 s20i model is also planned, which will be powered by a 2.0 liter four-cylinder unit packing 180 hp and 200 lb-ft of torque, while the s30i is expected to be powered by the same engine with 248 hp and 258 lb-ft. BMW will be presenting the final production version of the new Z4 next year, where the M40i will likely be part of the launch line-up.