The secret BMW M CSLs part 2: V10 E60 M5 CSL and the V10 E63 M6 CSL

Ever since BMW’s M Division started business back in 1972, only three cars have ever officially worn the ‘CSL’ moniker. The original 3.0 CSL everyone of a certain age gets gooey over, the E46-generation M3 CSL that warms the dark heart of the internet, and the latest M4 CSL. However, there were four secret CSL prototypes that never saw the light of a Munich day, at least until now.

In part one, Top Gear magazine's Ollie Marriage looked at an E46 M3 CSL with an E39-gen M5's V8 shoehorned under the bonnet, and a prototype F87 M2 CSL that featured elements from the M4 GTS. Click here in case you missed it.

In this second part, Ollie looks at two secret CSLs from the generation of M that famously went hardcore: the E60 M5 and the E63 M6. Both shared a 5.0-litre naturally-aspirated V10 engine making them the most uncompromising M cars of the time. Yet the folks at M Division still went ahead and secretly intensified them, by boring and stroking the engines to 5.4-litres to produce over 540hp and giving them the full CSL lightweighting treatment...