Since BMW confirmed the new M3 and M4 will debut this September, our spies have spotted prototypes of the sports sedan and coupe undergoing testing with less camouflage than before. But while these were separate testing sessions, the new M3 and M4 have now been spied being tested together for the first time on picturesque roads in Southern Europe, allowing us to see how they compare.

Once again, the new M3 adopts a four-door body style, while the M4 will be sold as a more stylish two-door sports coupe. There was a time when the BMW M3 was sold as either a sedan or coupe, but this hasn't been the case since the BMW M4 Coupe was introduced in 2014.

With two extra doors, the new M3 will inevitably be heavier than the M4, but the M4 Coupe appears to be slightly longer than the M3 Sedan. Other than that, the new BMW M3 and M4 will be practically identical mechanically and visually, just like the current-generation models.

Both the new BMW M3 and M4 will ride on the latest version of BMW's CLAR platform, meaning they will be lighter and more agile than their predecessors. The enormous kidney grille inspired by the controversial BMW 4 Concept is also being applied to the new M3 and M4. It makes sense to make the M4's front design consistent with the new 4 Series, but the larger grille looks more jarring on the M3 in contrast to the 3 Series' smaller nostrils.

We also get a closer look at the new BMW M3's grille, as our spies spotted the performance sedan being put through its paces at the Nurburgring. Larger air intakes, wider wheel arches, and a quad exhaust system also set the new M3 and M4 apart from their standard siblings.

As for technical specifications, the new BMW M3 and M4 will be powered by a twin-turbo 3.0-liter straight-six engine producing 480 hp in the base model and 510 hp in the more powerful Competition variant. The base M3 and M4 will only be offered with a six-speed manual transmission and RWD, whereas the track-focused Competition will be sold with an eight-speed automatic transmission and AWD. BMW will share more details when the new M3 and M4 are unveiled in mid-September.