On July 7, 2000, about 1100 eastern daylight time, a Cessna P210N, N7VZ, registered to Donatech Corporation, crashed while attempting to land, following loss of engine power during takeoff from Boone Airport, Boone, North Carolina, while on a Title 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft received substantial damage and the private-rated pilot received serious injuries. The two passengers received minor injuries. The flight was originating at the time of the accident. The pilot stated that upon takeoff rotation, power significantly decreased and there was a noise from the engine at the same time. On climb-out, the engine power and noise oscillated and power reduced. The aircraft failed to climb. At this point he had insufficient runway left to land. He began to maneuver the aircraft for a 180-degree turn back to the runway. As the turn progressed he found he had not enough power to complete the turn in order to land on the runway. The aircraft landed adjacent to the runway onto the grassed area. The aircraft began to skid, the nose wheel collapsed and then continued to slide until it contacted a large mound of dirt upon which the aircraft came to rest. Postcrash examination of the aircraft by an FAA inspector and a representative of Teledyne Continental Motors showed that the aircraft and engine had been modified by the installation of a Riley International Corporation, Engine Inter-cooler System, in accordance with FAA Supplemental Type Certificates SA 2528 NM and SE 2529 NM. The single attach point for the inter-cooler had a worn bolt hole and the inter-cooler could be moved. The rubber duct which connects the outlet of the inter-cooler to the engine was split about 50% around, allowing turbocharged air to be exhausted overboard. The aircraft had received an annual inspection on June 13, 2000, about 1 flight hour before the accident. The Riley International Corporation, Airplane Flight Manual Supplement and Pilot Operating Handbook Appendix, did not give any instructions for inspection of the inter-cooler system.