In typically infuriating M division fashion, BMW has finally built an M5 CSL. Well, they’ve built one and it’s not for sale…Ostensibly constructed to pay homage to a quarter century of M5 four-door performance madness, this one-off M5 CSL is aptly described by M division boss Albert Biermann as, “the M5 CSL we never built.”Based on the E60 platform and finished in classic BMW triple-stripe racing livery, the M5 CSL will have current owners of BMW’s supersaloon reaching for the defibrillator. 5.5l V10Powered by a stroked version of the M5’s 5l V10, the CSL’s 5.5l engine benefits from added modifications including a carbon-fibre intake and secondary oil cooler. Outputs for the M5 CSL have not been officially vetted. M division boss Biermann hints at increases of around 57kW and 30Nm over the stock M5 though, ushering in a power peak of 430kW and maximum rotational force of 540Nm.Transferring the additional power to M5 CSL’s rear axle is toughened version of the Getrag seven-speed dual-clutch transmission which does duty in BMW’s M3 range, supplanting M5’s hateful SMG transmission. Any BMW sporting CSL sensibilities (even if it’s a one-off) needs to show off some keen weight loss credentials. To this end M5 CSL obliges with a carbon-roof and carbon shelled front seats (the rear bench is binned completely) which melt away 50kg of mass. BMW is coy about the M5 CSL’s performance potential, only hinting it dips under the eight minute barrier around the Nurburgring – which should leave you to draw your own conclusions.