BMW won’t give the Z4 roadster a full-fat M version as the lineup tops out with the M40i, now with a manual gearbox as well. However, there might be a Z4 M Coupe substitute from Toyota considering a Supra GRMN is in the works. A new spy video shot at the Nürburgring shows a prototype of the Japanese sports car being tested with a BMW engine.

The million-dollar question is: Does the sound come from the B58 or the S58? The former is a single-turbo engine already used in the regular Supra (and the Ineos Grenadier) while the latter is a twin-turbo mill that goes into the M2, M3, M4, X3 M, X4 M, plus ALPINA’s B3 and B4. Reports suggest the Supra GRMN is getting the more potent S58 to provide a healthy boost from the regular model’s 335 hp and 369 lb-ft (500 Nm).

If the S58 fits underneath that hood, we are not expecting M4 levels of power as Toyota is likely to dial the 3.0-liter engine to be roughly on par with the M2 G87, which has 453 hp and 406 lb-ft (550 Nm). It’s expected to be sold strictly with rear-wheel drive but it’s unclear whether a manual gearbox will be available. Additional upgrades will include an aerodynamic package with a massive rear wing and front canards. The prototype seems to be sitting lower to the ground, presumably thanks to a stiffer suspension setup.

Chunkier brakes with drilled discs are likely on the menu, along with bespoke wheels wrapped in low-profile tires. Chances are chassis tweaks and interior upgrades are being worked on for the GRMN to earn its acronym, which stands for “Gazoo Racing Masters of the Nürburgring.” Interestingly, this prototype’s license plate shows it’s been registered in Munich where BMW calls home whereas Toyota Gazoo Racing has its European headquarters in Cologne.

Toyota has been testing the Supra GRMN for a while, so we’re expecting the world premiere to take place later in 2024. It remains to be seen whether it’ll be a permanent member of the lineup or a limited-run special edition. The high-performance coupe is built by Magna Steyr in Graz, Austria alongside the Z4 convertible.

Source: CarSpyMedia / YouTube