British race-driver Ken Rudd constructed the very first Ace-Bristol, but his hybrid was quickly adopted by the AC factory. First shown in autumn 1956, the AC Ace-Bristol was in production by the spring of 1957. Because it was not only more powerful than AC’s own engine but capable of a lot more power-tuning, the Bristol unit made these cars, especially the Ace, much more suited for competition. The roots of the AC Ace-Bristol design go back to the Thirties, when BMW engine design chief Fritz Feider produced a series of six-cylinder engines that culminated in the 1971-cc unit of the fabled 328. After World War II, Bristol of England “acquired” the design by somewhat dubious means (see Bristol Sports Cars) and manufactured it in the UK. By the mid-1950s, Bristol was happy to supply this noble engine to other automakers.

Complete with three downdraft Solex carburetors, the Bristol engine was tall but fit comfortably under the AC Ace-Bristol  hood. It had pushrod overhead valve actuation (via complex linkages), part-spherical combustion chambers, and a very long stroke. Despite all this, it was amazingly flexible and high-revving.