On August 6, 1996, about 1820 eastern daylight time, a homebuilt Velocity, N637KM, registered to a private individual, nosed over during a precautionary landing in a field near Dublin, Georgia. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 91 personal flight. The airplane was substantially damaged and the commercial-rated pilot, and two passengers were not injured. The flight originated about 1700 from the Cobb County-McCollum Field Airport, Marietta, Georgia. The pilot stated to an FAA inspector that en route he first heard engine roughness then observed high oil temperature and experienced momentary binding of the aileron flight controls. The engine began to run rough and the oil temperature reached maximum red line. He initiated a forced landing in a cotton field and after touchdown, the nose gear and a section of the left wing separated. The airplane then nosed over and came to rest inverted. Examination of the engine by the FAA inspector revealed that the exhaust for the Nos. 2 and 4 cylinders were separated at the flange at each cylinder. The exhaust was manufactured by Velocity using 16 gauge 304 stainless steel purchased by the owner/pilot and was installed about 96 hours earlier. No determination was made as to the reason for the failure of the exhaust.