AC's famous John Weller-designed, 1,991cc, overhead-camshaft six-cylinder engine entered production in 1922, later helping to secure the marque's place in motoring history when in 1926 a 2-litre AC became the first British car to win the Monte Carlo Rally. Financial difficulties saw AC taken over by the Hurlock brothers in 1930 and from then on the firm concentrated on sporting cars aimed at the discerning enthusiast. AC's long-established three-speed transaxle gave way to a conventional four-speed unit gearbox on the 1933-introduced 16/56 and 16/66 2.0-litre models, which also came with a new chassis and Bendix brakes. The chassis became under-slung with cross bracing in 1934 and gained a synchromesh gearbox the following year, these improvements being incorporated in the 16/60 and 16/70 models launched in 1936. Also new that year was the short-wheelbase 16/80, which with Arnott supercharger became the 16/90, the latter newly introduced in 1938. Fewer than 600 post-1933 standard 16hp cars are thought to have been built before production ended in 1939, all of which were powered by Weller's 2.0-litre six.