Power for the model comes from a turbocharged 2.0-litre engine producing 154bhp and 177lb ft. That is enough to propel the six-speed manual sDrive18i from 0-62mph in 7.9sec and on to 137mph. Combined fuel economy is rated at 41.5mpg, with CO2 emissions of 159g/km.
An optional eight-speed automatic is also offered.
The engines in the other Z4 models - sDrive20i, sDrive28i, sDrive35i and sDrive35is - continue unchanged.
Cosmetically, the changes to the facelifted roadster are minor, the revised LED headlights being the stand-out change. New alloy wheel options are offered, while there are minor exterior trim detailing changes.
Other changes include the option of a new Design Pure Traction styling pack, which adds contrasting black and orange trim to the cabin. The interior also features new gloss black trim for the air vent and iDrive surrounds as standard. Leather trim is also standard for the sDrive28i models and above, with a Fineline Anthracite wood finish available as an option.
The M Sport package - comprising bespoke suspension settings, alloy wheels and exterior and interior trim - is again offered, with a more focused version of this pack available on the sDrive35is range-topper.
The revised Z4 is due to reach the UK in April.