THE PILOT VISUALLY CHECKED THE FUEL BEFORE TAKEOFF AND WAS AWARE THAT THE TANKS WERE NOT FULL. HE REPORTED THAT HE WOULD ONLY USE 80/87 OCTANE FUEL BECAUSE THE ENGINE WAS NOT EQUIPPED WITH VALVES THAT WOULD ACCEPT 100 OCTANE FUEL. DURING THE FLIGHT, HE ENCOUNTERED CLOUDS AND DIVERTED FROM HIS ORIGINAL ROUTE. THE LEFT FUEL TANK WENT DRY ABOUT 20 MILES SOUTH OF PHOENIX FIELD, FAIR OAKS, CA. HE SWITCHED TO THE RIGHT TANK AND PROCEEDED TOWARD PHOENIX FIELD. THE PILOT SAID THAT HE CHECKED THE RIGHT FUEL TANK GAUGE AFTER SWITCHING TANKS AND IT SHOWED A LITTLE LESS THAN HALF FULL. HOWEVER, WHILE THE PILOT WAS DIVERTING, THE ENGINE LOST POWER AND WOULD NOT RESTART. THE AIRCRAFT WAS SUBSTANTIALLY DAMAGED DURING A LANDING ON ROUGH, HILLY TERRAIN IN AN AREA OF TREES AND BRUSH. THE ELEVATION OF THE CRASH SITE WAS APPROXIMATELY 4500 FT MSL.