On July 18, 2010, at 1402 mountain standard time, a Beech A36, N9SH, was substantially damaged when it hit a automobile during an emergency landing about 1 mile west of the runway at Deer Valley Airport (DVT), Phoenix, Arizona. The private pilot, the sole occupant, received serious injuries. The driver of the vehicle, the sole occupant, received minor injuries. The maintenance test flight was conducted under the provisions of 14 Code of Federal Regulations Part 91, without a flight plan. Visual meteorological conditions prevailed. The local flight originated about 1300. According to a Federal Aviation Administration (FAA) inspector who responded to the accident scene, the engine lost power. During the forced landing, the airplane hit an automobile. The right wing and wingtip fuel tank were substantially damaged. Both tip tanks were compromised. The inspector reported that 1.5 gallons of fuel was recovered from the right wing tank and that the left fuel tank was empty. The left wing fuel tank was not damaged; however, the right wing fuel tank was cracked and had leaked fuel. The pilot was interviewed by an FAA inspector. The pilot reported that he had just completed a 'top overhaul’ of the engine and was performing a maintenance flight to break in the new cylinders. The pilot reported flying for about an hour at 10,000 feet. He decided to descend to a lower altitude; 6,500 feet, and continue operating the engine for another hour. As he changed altitude, he switched the fuel tank; he thought that the airplane fuel gauge was sticking because he knew there was fuel in the tank, and the airplane was still flying. As he contemplated the fuel gauge, the engine stopped running. The pilot stated that he was just north of DVT and set up for a landing. As the airplane turned onto final; the pilot realized that the airplane did not have enough altitude to make it to the airport, so he decided to land on Deer Valley Road. The engine was examined under the supervision of an FAA inspector. The inspector reported that there were no anomalies with the engine; however, the magneto would not produce a spark. Further examination of the magneto revealed a cracked magneto cap consistent with impact damage. The cap was replaced and the magneto performed as designed. An examination of the remaining aircraft systems revealed no anomalies. The pilot did not submit the required Pilot/Operator aircraft accident/incident report form.