Lycoming R-680 on the Boeing-Stearman Model 75

 Lycoming R-680 is a nine-cylinder air-cooled radial engine, rated at 225hp at 2100 rpm, the first engine produced by Lycoming. The engine was produced in two types the E and B series both are essentially the same, the B4E was available in a trainer version with a front exhaust collector for use without cylinder air baffles.