On September 21, 2015, about 1040 central daylight time, a Cessna 421B airplane, N813CA, sustained substantial damage after a loss of engine power and runway excursion at Platteville Municipal Airport (PBV), Platteville, Wisconsin. The commercial-rated pilot and passenger were not injured. The airplane was registered to Blue Hansa LLC and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed at the time of the accident and an instrument flight rules flight plan was filed. The flight was originating at the time of the accident. The pilot reported he completed a preflight inspection of the airplane per the checklist and checked the weather. He taxied to the end of runway 15 and completed the pre-takeoff checklist, which included an engine run-up for each engine. There were no anomalies noted during the pre-flight or pre-takeoff checklists. He taxied onto the runway and advanced both throttles full forward. At 85 knots, just before the runway 7/25 crossing, he started rotation and noticed the right engine manifold pressure decrease and felt a power reduction. He aborted the takeoff; he pulled back both throttles and applied the brakes "hard." The airplane continued on the runway for about 1,000 ft then off of the runway into the grass and a soybean field where it came to rest. The responding Federal Aviation Administration (FAA) inspector documented the witness marks left from the accident airplane on the runway and grass surfaces. There were airplane tire skid marks on the last 1,000 ft of runway pavement and tire marks in the grass for 290 ft off the end of the runway where the terrain slopes downward. The tire marks were not present for about 90 ft consistent with the airplane becoming airborne until the airplane impacted the ground again and the gear collapsed. The witness marks in the grass continued for another 90 ft where the airplane came to rest in a soybean field. Runway 15/33 at PVB is 3,999 ft in length. The intersection of runway 7/25 is about 3,000 ft from the beginning of runway 15; the remaining runway distance from the intersection to the departure end of runway 15 is about 1,000 ft. According to Cessna 421B operating manual, the distance needed during an accelerated stop with a decision speed of 85 knots is about 2,400 ft. The right engine was sent to Continental Motors, Inc (CMI) in Mobile, Alabama for examination and an engine test run, which were completed on January 4 and 5, 2015. The right engine was received intact with no signs of significant impact damage. The cylinders were borescoped; the cylinders, piston faces, and valve heads displayed normal operating and combustion signatures. The magneto-to-engine timing was checked, the exact timing was not determined because it was about 5º past the specified timing scale visible from the engine timing plug. The right engine was mounted on a test stand for functional testing. The engine started normally, on the first attempt with no signs of hesitation in RPM. The propeller was out of track because the propeller flange was bent. Shims were placed between the propeller flange and hub to bring the propeller back in track. The engine was restarted, and the engine RPM was advanced in steps for warm-up in preparation for full power operation; the engine run time was limited due to the damage to the propeller flange. Throughout the test phase, the engine accelerated normally without any hesitation or interruption in power and demonstrated the ability to produce rated horsepower.