BMW M finally let a fan and a camera crew into its secret museum of prototypes. The fan is Ede Weihretter, a driving instructor at the BMW M Experience, his host is Hans Rahn, the head of vehicle prototyping, manufacturing concept and integration at BMW M. Rahn pulls out eight cars to Weihretter, examples of CSL projects that never got out of the experimental stage. The first is a prototype E46 M3 CSL; remember, the 2003 E46 M3 was only the second-ever CSL model after the 1973 3.0 CSL. The production CSL used the standard car's naturally aspirated 3.0-liter inline-six making 360 horsepower. The "crazy experiment" prototype stuffed a 4.0-liter V8 into the engine bay, negating a fair bit of the coupe's 220-pound weight loss but upping output to 423 horses — a recipe most performance cars have followed ever since, although BMW couldn't know that at the time.
The second treat is a prototype E60 M5 CSL, the bad boy with the 500-hp V10 and a manual transmission. Instead of the SMG III semi-automatic gearbox, engineers kept the SMG's looks but swapped in a dual-clutch transmission from Getrag that would later head to the M3. This proto was also the first M5 to get a carbon roof, the roof hidden under a wrap because the more mature M didn't need to advertise all of its tricks.
There's one more car featured in this episode that could have been a CSL but wasn't. However, at one point in the vid, Weihretter starts to wander among the toys on hand and Rahn says, "Stop. Let me show you around." So we'll let him do that, and we'll look forward to episode two.