The original 1961 Mini Cooper had a 997 cc engine. It was created through a collaboration between Mini designer Alec Issigonis and racing specialist John Cooper, who saw that the small front-wheel-drive car could become a serious competition machine.
The Cooper’s engine was derived from the Morris Mini-Minor unit but modified with a longer stroke, increasing displacement to 997 cc and raising output from roughly 34 bhp to 55 bhp. The car also received twin SU carburettors, a closer-ratio gearbox, and front disc brakes—unusual performance equipment for such a small road car at the time.
BMC commissioned 1,000 examples to satisfy Group 2 rally homologation requirements. This 997 cc specification was short-lived: in 1964, it was replaced by a shorter-stroke 998 cc engine. The 1,275 cc figure is associated with later Cooper S versions, not the original 1961 Mini Cooper. The 850 cc engine, meanwhile, belongs to the standard early Mini rather than the first Cooper.