What was found
CLIMBING THROUGH 13,000 MSL THE PILOT REPORTED A LOSS IN MANIFOLD PRESSURE ON THE LT ENGINE. RETURNED TO THE AIRPORT FOR A NORMAL LANDING. DURING INSPECTION, FOUND HEAT AND EXHAUST STAINING ON THE LOWER COWL. AFTER REMOVING THE COWLING, FOUND APPROXIMATELY 4 INCHES OF THE EXHAUST BALANCE TUBE WAS MISSING. THE MISSING PIECE WAS NOT IN THE COWLING.