Z4 M40i
B58 Gen 2

The G29 carries a slightly stronger factory rating than most of the BMWs running the same Gen 2 B58, though the mechanical package is shared. It makes no difference to tuning: Samuel's Stage 1 target of 440 bhp and 680 Nm applies regardless of which rating your car left the factory with, and the file is calibrated to your individual car either way.

Yes, with respect. The Z4 M40i's electronically controlled limited-slip differential and wide rear tyres manage Stage 1 torque well in the dry, while in the wet the traction systems step in earlier than they would on an xDrive saloon. Samuel shapes the delivery so torque builds progressively rather than arriving in a lump, which matters more in a short-wheelbase roadster than anywhere else.

Mechanically they are the same platform, sharing engine, gearbox and ECU, so the stages and targets match, and the Z4 benefits from the enormous Supra aftermarket for hybrid turbos, downpipes and fuelling hardware. The calibration is still done per car: a Z4 map is written for your Z4, not recycled from a Supra file.

A downpipe, which means an OPF delete on these cars, plus an intake, followed by a recalibration that takes the roadster to 480 bhp and 700 Nm on the standard turbo. The exhaust change also lets more of the straight-six's voice out, which on a car with a folding roof is half the point.

Arguably more than for a daily. There is no need to book the Z4 in anywhere or lose it for a day: the file arrives in your bootmod3, MHD or MG Flasher account within 24 hours of ordering, flashing takes a quarter of an hour at home, and the stock calibration is kept so winter storage or resale can happen on the factory map.