The M vault includes an M5 CSL and V8 M3 CSL.
BMW's M Division is celebrating a historic milestone this year: 50 years of production. To honor its 50th anniversary, BMW is pulling out all the stops, including a special roundel emblem, reviving the CSL moniker on the M4, and revealing new products like an M3 Wagon. As part of the year-long celebration, BMW will show off eight prototypes, some of which have never been shown to the public, contained in what the company is calling its M Secret Garage.
In part one of a multi-part series, BMW showed off three of the eight cars, all part of unreleased CSL development. The first car shown looks like a standard E46 BMW M3 CSL on the surface. However, under the hood, the M3's S54 inline-six motor is nowhere to be found. Instead, this M3 CSL Prototype E46 packs the E39 M5's S62 V8 inside. Whereas the production M3 CSL produced 360 horsepower from its CSL-spec I6, this V8 produces 426 hp. BMW also cut 242 pounds out of the car with a lightweight interior and other weight-reducing measures.
The only car we recognized was the E60-generation BMW M5 CSL, which was built as a one-off in 2009. It packs a bored-out V10 engine, now displacing 5.5 liters, producing around 621 horsepower at a whopping 9,000 rpm. Inside, the interior was mostly stripped out, shaving off 110 pounds, and this car even had a dual-clutch transmission unlike the production car. Sadly, this car never made it past the development stage.
The video also shows a similar car, an E63-generation BMW M6. This car also contained the S85 V10, though this one is stock aside from a carbon fiber engine cover. Inside, this particular M6 has a stripped out interior with suede surfaces with two switches to control the prototype active aerodynamics. BMW was testing a pop-up spoiler and electronically operated front splitter that never made it to the production M6.
At the end of the video, BMW teases that it has more to show in part two, coming soon.