Automobile Magazine says the highly-rumored BMW M4 GTS might be instead called the BMW M4 CSL. The change in moniker might be related to the fact that both Porsche and Mercedes use GTS acronym and the CSL name is a legend in BMW’s history. The “CSL” moniker, a model name created in the early 1970s for the legendary BMW 3.0 CSL “Batmobile” and appeared again in the E46 M3 CSL.
“CSL” stands for coupe sport lightweight and BMW says the acronym applies to the new, sporty M4. The M Division aims to shed 220 pounds from the weight of the current M4 Coupe. So the hood, doors, and a trunklid are made of aluminum (just like the regular M4), while manually adjustable carbon-fiber front seats (and no more rear seat) are part of the package. The rollcage will be an optional extra.
The M Performance aero kit will include a front splitter and fender blades, rocker-sill extensions, carbon fiber mirrors, a smoother underbody cover, a rear aero diffuser, and a size-XXL tail rudder.
BMW M4 CSL will feature the S55 engine with a water injection kit, which will be used to cool the intake charge. The use of water injection solves a problem that occurs under certain high pressure conditions on forced induction engines. When significant pressure is applied to the intake air charge, the temperature of the charge increases – the act of pressurizing the charge also heats the charge up (squeeze something and it will heat up as it compresses). Inter-cooling has been used to great advantage to mitigate this problem but when you want to increase power (by increasing boost pressure) beyond the capacity of a installable inter-cooler, you need to think about water/methanol injection. The job of the water in the kit is to cool the intake air by absorbing heat when the water is converted from a liquid to a gas (steam). Methanol is often included in the mix for anti-freeze properties as well as methanol’s inherent octane enhancement (anti-knock capabilities). And it is premature ignition (or knock ) that the water injection kit also protects against. Knock can cause havoc in an engine; it is by definition an uncontrolled burn (or a burn of the fuel that occurs without an external spark – the result of an extremely hot combustion chamber).
So, to increase boost pressure (and subsequently power) in the S55 variant installed in the M4 MotoGP, it appears that BMW has decided to implement a water injection sequence under very specific operating conditions. The water is injected (a fine spray where the droplets are so small that almost all of the water in the drop is on the surface of the drop), the heat of the compressed charge air is absorbed by the injected water, which then cools the charge air.
The water-injection technology is expected to add about 22 pounds to the car thanks to the requisite plumbing and a separate water tank.
BMW M4 CSL will have 500 hp from the 2015 M4’s 431 hp at 5,500-7,300 rpm and maximum torque climbs to 443 lb-ft from the current car’s 406 lb-ft @ 1,850-5,500 rpm.
750 units of the 2016 BMW M4 CSL appear to be planned.