Despite the low demand for luxury motorcycles during the Great Depression, Indian not only continued production of the Four, but continued to develop the motorcycle. One of the less popular versions of the Four was the "upside down" engine on the 1936-37 models. While earlier (and later) Fours had inlet-over-exhaust (IOE) cylinder heads with overhead inlet valves and side exhaust valves, the 1936-1937 Indian Four had a unique EOI cylinder head, with the positions reversed. In theory, this would improve fuel vaporization, and the new engine was more powerful. However, the new system made the cylinder head, and the rider's inseam, very hot. This, along with an exhaust valvetrain that required frequent adjustment, caused sales to drop. The addition of dual carburetors in 1937 did not revive interest. The design was returned to the original configuration in 1938.