Coupe, Sport, Lightweight: those are the three tenets of BMW’s CSL-badged efforts, offering a level of performance even beyond what Munich engineers for its comparatively ordinary M cars. In an over the weekend, BMW prototyping chief Hans Rahn brand pulled the covers off three CSL prototypes designed in the early-to-mid aughts. Each is truly one-of-one, and although they never received production runs as you see them, the technologies and ideas they spawned would go on to inform future M machines.

For example, take the first vehicle we see: an E46 M3 CSL with a distinction, so hinted by the second round aperture drilled into its front bumper. This was done to increase airflow because this M3 just so happens to house the V8 out of an E39 M5, good for 425 horsepower. That works out to be about 65 hp better than the production CSL, and 10 hp beyond what the S65 V8 in the later E92 M3 pulled.

There’s also an M-liveried E60 M5 with a carbon roof and a Getrag-sourced dual-clutch transmission before BMW debuted that gearbox in the E92. Here, M engineers extracted 621 hp from the sport sedan’s five-liter V10, good for an improvement of about 120 hp over your typical E60. Sure, it’s technically not a coupe and might not even be all that light, but I think we can excuse semantics here.

And then there’s the E63 M6 CSL, where the M team paid less attention to the powertrain and was more concerned with making the car more stable at high speeds. To achieve this, active aero elements were added to the front and back, in the form of a splitter that drops down from just behind the underside of the front bumper, plus a rear wing. The wing especially seems to be a very refined part that exhibits production quality, indicating that the M crew was treating this less like a skunkworks experiment and more like a project with a commercial future in mind. Eagle-eyed enthusiasts will also notice the Doppelsteg-style side mirrors, a shape that would later find its way into production M cars.

This is only the first exploration into BMW’s secret CSL garage, as there’s a part two planned. It’s always so enjoyable when BMW gives us a peek the at vehicles that never were; more manufacturers should follow suit.