The Mercedes-Benz SL-Class is a grand touring car manufactured by Mercedes since 1954. The designation SL derives from the German Super-Light. The original idea was suggested by American importer Max Hoffman, who perceived a market for a toned-down Gran Prix car tailored to affluent performance enthusiasts in the booming post-war American market, which remains the primary market for the vehicles. The SL designation was first applied to the 300 SL, often referred to as the "Gullwing" due to its gullwing or upward-opening doors. The term SL refers to the marketing variations of the vehicle, including the numerous engine configurations spanning six design generations. A mid-cycle facelift was introduced in 2016 for the 2017 model year. Launched early 2016 in California, the revised SL400 featured a 3-litre 362 hp biturbo V6 mated, for the first time in the SL, to Mercedes' own 9G-Tronic PLUS 9-speed automatic transmission. An SL500, with a 4.7-litre biturbo V8 producing 449 hp, was likewise paired with the 9G-tronic PLUS transmission. The Mercedes-AMG SL63 (577 hp) and SL65 (621 hp) variants continued with virtually unchanged powertrains, paired with AMG's SPEEDSHIFT MCT 7-speed sports transmission with claimed improved shift times. Cosmetically, every SL received a revised front end, front grille treatment and larger non-functional side 'vents' behind the front wheels. All variants also received adaptive LED front headlights with integrated daytime running lights and turn signals, leaving the below-bumper intake area free from lighting. The LED tail lights received single-colour red or red-and-amber lenses instead of the red and white of the pre-facelift models. Front and rear bumper assemblies were redesigned to align more closely with recent models introduced by Mercedes, while selected convenience and driver assistance technologies, introduced earlier on various other Mercedes models, were made optionally available, including revised Active Body Control, now with the "Curve Tilting" function from the S-Class Coupe. Externally, the SL63 and SL65 were distinguishable from the non-AMG variants by embellishments to their bumper assemblies and side sills in gloss black or polished aluminium, respectively. The SL63 and SL65 also featured trademark AMG 'twin lamella' front grilles and dual twin tailpipe exhaust trims as well as a carbon fibre composite trunk lid. A slight revision to the folding 'Vario-roof' hardtop operation meant it would continue to deploy at speeds up to 25 mph (40 kph) once initiated and the luggage compartment partition, required to prevent the hardtop components, when folded, and any luggage compartment contents coming into contact with each other, no longer had to be deployed in a separate manual operation. Interiors continued virtually unchanged with the exception of slightly revised minor switchgear and a redesigned steering wheel.