What was found
A NORMAL FLIGHT WAS COMPLETED. THE NEXT TAKEOFF RESULTED IN ONLY A 26.50 INCH MANIFOLD PRESSURE (NORMAL RED LINE 32.50 INCHES). AFTER TROUBLESHOOTING THE PRE SSURE RELIEF VALVE AND TURBO CONTROL VALVE, THE TAILPIPE WAS REMOVED AND DISCOVERED THE WASTEGATE BUTTERFLY VALVE WAS MISSING AND HAD ENTERED THE ACFT THROUGH THE TAILPIPE. SUBMITTER STATED THE MOST OBVIOUS CAUSE IS EXCESS TIME IN USE. T IME SINCE OVERHAUL 1,482 HRS (1,400 TBO) JUST UNDER 13 YEARS.