I know a Nova racing engine in a 1/10 tourer can get 125 to 130 C, I have seen simple Kyosho engines up to 170 C and my own Eagle 100 and 130 C with 2 different pipes and a Sirio 3.5cc on 85 to 90 C and some engines I test only 75 C.

In other words, there is no right number to tell. Be sure there is smoke to see from the exhaust and the engine performs good without hickups then the temperature will be OK.