On March 4, 2001, at 1037 hours mountain standard time, a Harlow Lancair ES, N350N, was substantially damaged during a forced landing in a field near Marana, Arizona, due to smoke emanating from the engine cowling. The private pilot sustained minor injuries while the sole passenger was uninjured. Visual meteorological conditions prevailed during the flight from Casa Grande to La Cholla Airpark, Arizona. The flight was conducted by the owner under 14 CFR Part 91. The airplane departed Casa Grande at 0910, and no flight plan was filed. The pilot stated that during his flight from Casa Grande to La Cholla, he noted smoke coming out of the cowling as he neared Marana. He reduced power and initiated a precautionary landing, intending to land at Marana Northwest Regional Airport. As he descended, he realized that he was not going to make the airport and applied power to slow the descent. The engine responded to the throttle input, but the propeller did not. The pilot stated that when he realized he could not make the airport, he directed the airplane to a plowed agricultural field. During the landing sequence, the nose gear "dug in" and collapsed; the airplane was nosed over. The airplane came to rest inverted. Both wings were substantially damaged. The right wing spar was broken and the left wing separated at the wing root. The pilot, who is also the builder of the airplane, noted that the propeller drive belt pulley had been heated and distorted, and the drive belt had separated. He noted what appeared to be spots of molten aluminum near the drive pulley. The pilot stated that the belt reduction drive bearing and belt had failed. The engine and reduction drive unit used on the accident airplane are derived from a marine application of an automotive engine. The Federal Aviation Administration approved manufacturer of the airplane kit stated that they do not support use of automotive or marine applications on their airplanes. The manuals and plans provided with the kit call for Continental or Lycoming engines only. The accident airplane used a marine version of the General Motors LT-1 350 automotive engine with a non certified V-belt reduction drive unit.