The Curtiss R-600 Challenger was a six-cylinder, double-row, air-cooled, radial engine for aircraft use built in the United States in the late 1920s. It developed 170to.
Curtiss started work on a small six-cylinder engine in May 1927. The engine was unusual in its design with aluminium cylinders mounted at 60°, so that it was in effect two staggered three cylinder engines. The engine was first run in December 1927, and was taken to market producing between 170and at 1,800 rpm.