G29 Tuning

Here's what makes the Z4 M40i interesting before you even drive it: it's the Toyota GR Supra's twin. The two were co-developed on one platform with the same B58 straight-six — so the M40i is, mechanically, a drop-top Supra wearing a BMW badge (around 335 hp here).

Which means everything the B58 does in the M340i, it does in the Z4 (the full story's on the G20 page) — a calibration and bolt-ons scale it the same way — except now it arrives in a short, rear-drive roadster with the top down. The sDrive30i below it runs the B48 four (255 hp), the lighter-nosed handling pick; the M40i is the one that pairs real pace with open-air drama.

For a build, the pedigree is the appeal: the same engine the Supra crowd has already pushed deep into the 600s lives here, so the aftermarket is proven and deep. The honest notes are the B58 family's usual maintenance (the oil-filter-housing gasket; see the G20 page) and a roadster's slightly softer structure than a fixed roof.

So the Z4 M40i is the rare tunable roadster with a real performance bloodline — the Supra's engineering, BMW's cabin, and the sky overhead.