This is a rare Continental IV-1430 (inverted V12). The hyper engine (http://en.wikipedia.org/wiki/Hyper_engine) was a 1930s study project of the United States Army Air Corps, an effort to develop an aircraft engine capable of delivering 1 horsepower per cubic inch (46 kW/L) of engine displacement. The USAAC funded development of an engine of about 1200 cubic inches (20 L), hoping the engine's smaller size would lead to better streamlining and improved range. The engine did not enter volume production because it had been matched by existing designs by the time it was perfected.
This is an interesting story of one. http://www.enginehistory.org/iv-1430.htm
Check out the video of it running. Link at top of page.
I love internal combustion engines!