Liquid cooled I think the Isotta-Fraschini Omega RC.40 at the moment giving 1930hp at 4000m. Its big and heavy. Rolls-Royce Vulture should give similar power when its ready soonish. First flight of Tornado prototype was 1936 I seem to remember from news.
Air cooled I'm not so sure. R-2600 should be around soonish at 1600hp, R-2800 at 1850hp, R-3350 with over 2000hp but not reliable. Alfa-Romeo 135 at around 1700hp but with reliability problems. BMW 139 is less powerful but not reliable. Bristol Hercules is a bit down on power.