Putting a 9-cylinder 150 horsepower Rotec Radial R3600 aircraft engine on a custom chopper frame with a tiny propeller is just as insane as putting a 10-liter radial engine into a Goggomobile. It's nuts, and wonderfully so.

The first BMW product may have been an aircraft engine, but it took help from the United States to return BMW to their roots after World War I put an end to German aircraft engine production. This BMW 132 radial nine began life in 1926 as the Pratt & Whitney Hornet and went on to power thousands of Luftwaffe planes,…