This question has been discussed to death on this site without consensus... I have the same issue and don't know whether to be concerned or not. In fact, I am willing to bet that MOST of the super cubs out there run this hot!
Flying up to and around Alaska this summer I have made it a point to ask every cub owner and pilot what CHTs they run. Here is a sampling of the responses and observations:
- From Lycoming factory rep at a flyin in PA: 400 to 430 in cruise is ok - our engineers set those numbers for a reason, they are in the manual.
- From a well known A&P/IA on this site I visited on the way up: I cruise at up to 450 in my 150HP cub without any issues all the time.
- A commercial operator with a 160 HP in a remote part of Alaska: we are seeing CHTs up to 480 in climb, and we have to take corrective action to bring it down. We cruise at over 430 all the time.
- From a well known supercub.org member up here: read the Lycoming manual... they are right. And rip that damn CHT gauge out and stop worrying!
- From a well known bush pilot for something like 40 years up here: I don't have any CHT gauges in any of my aircraft. Oil temp is what's important! Look at all those Florida banner tow pilots that don't run any cowling at all!
MOST of the cubs here in Alaska don't have any CHT gauges and have no idea what temps they're running... and also don't seem to appreciate the airflow issues that Steve refers to! Many have wide open bottom cowls where the air filters and starter holes are.
But I can't help worrying that running this hot will not cause some damage, and have been taking all the recommended steps to bring mine down (so far without success). My manometer readings have been between 5.5 - 6 inches as recommended by Lycoming... that's with a slow 160 HP cub with 31" bushwheels, etc.
Just some observations.... wish I knew the answer, especially when flying in some of these really remote areas...