Two new prototypes of the upcoming BMW M4 CSL have been spied in the midst of testing, both sporting unique front grilles. The massive kidney grilles of the new BMW M3 and M4 have been a point of controversy since the cars were unveiled almost 12 months ago. While the M4 CSL’s kidney grilles will be the same basic shape of those of the standard car, we can see that the inserts are different and give the sports car a more aggressive and muscular look. Of course, it’s difficult to say if these grilles are identical to the ones that will be fitted to the production model, but we suspect that they are.

Of course, it is not just the unique grilles that will differentiate the M4 CSL from the standard model. BMW will also equip the car with a new splitter. While not visible in these photos, the CSL will also get unique side skirts and a tweaked rear end with an enlarged lip spoiler and a different diffuser.

Powertrain details have yet to be confirmed but a recent report claims the car will have a modified version of the standard model’s 3.0-liter twin-turbocharged six-cylinder, albeit modified to produce roughly 540 hp. It has also been asserted that the model will be sold exclusively in rear-wheel drive form as opposed to the xDrive all-wheel drive of the current M4 Competition.

Coupled as standard to the engine will be an 8-speed automatic transmission and unlike the entry-level model, there probably won’t be a six-speed manual on offer. While that’s a shame, it’s not really a surprise.