If the cylinder where the muffler bolts go is reaching 450 degrees F., you have more problems than your muffler coming loose. The cylinder head itself, which is the hottest part, should never approach 450..... Yes, the exhaust gas temp itself may reach as high as 1300 to 1400 degrees on a lean run (more like 1000 to 1100 degrees normally), but the cylinder itself never reaches that; at least not and stays serviceable....

AV8TOR