On July 21, 2007, at 1228 central daylight time, a Beech V35B Bonanza, N313W, piloted by a private pilot, was substantially damaged during a forced landing following a loss of engine power near Rockford, Illinois. The flight was being conducted under 14 CFR Part 91. The pilot was not injured. The flight departed Chicago/Rockford International Airport (RFD), Rockford, Illinois, about 1200. The intended destination was Wittman Regional Airport (OSH), Oshkosh, Wisconsin. The pilot stated that he was part of a formation flight of Bonanza airplanes that departed RFD en route to the Experimental Aircraft Association (EAA) AirVenture 2007 convention at OSH. He noted that about 10 minutes after takeoff, the engine "began to hesitate during large throttle excursions and faltered upon [application of] full throttle." He left the formation with the intention of returning to RFD. However, "the engine began making loud noises and the RPM sagged to 2,000," with the manifold pressure approximately 10 inches. He subsequently executed a forced landing to a cornfield. A post accident engine examination did not reveal any anomalies associated with a pre-impact engine failure. Condition of the cylinders was unremarkable when inspected using a bore scope. Spark plug wear appeared normal. Engine control continuity was confirmed. Subsequent to the examination, the engine assembly was mounted on a test stand and run for approximately 30 minutes. The engine was run at various speeds from 1,500 RPM to 2,700 RPM. Engine operation was responsive and smooth. Magneto drop was within manufacturer's requirements. Examination of the oil filter media was unremarkable and the fuel inlet screen was clean. No anomalies were detected during the engine run. Airplane maintenance records indicated that an overhaul of the engine was completed on June 6, 2007. At that time, it was converted from a Continental IO-520-BB engine to an IO-550-B-EE engine in accordance with Supplemental Type Certificate SE1791LA. According to the pilot, the engine had accumulated approximately 37 hours flight time since the overhaul and conversion.