The 911 RSR (991 series) took over from the 911 GT3 RSR 997 series starting from the 2013 season. Many changes compared to the GT3 RSR: longer wheelbase, new aerodynamics, improved weight distribution, new suspension design. The 4-liter engine, associated with a six-speed transmission, delivered 460 horsepower. Further evolutions were developed for the following seasons: in 2014 the RSR underwent some changes allowed by the regulation, with the engine developing a dozen more horses. Some new aerodynamic details were designed for 2015 and 2016, the year in which competition from Ferrari and Ford became quite difficult for Porsche. The new 911 RSR featuring a centrally positioned engine would make its debut in 2017.