there are a lot of things that determine the heat you READ from an engine

Type of temp gun
Emmesivity rating of the material in the head
Head Clearence
Fuel
Pipe
Tyres
Weather
Humidity

etc etc ..

What i did with the engines at the NSW titles was to see how far we could lean them and still run reliably with my new fuel. We found 160 deg C was about as far you could go while still maintaining good performance. id say with regular fuels run them at 140 deg c .

What people regard as hot may actually be normal operating temp. When you get an engine running so hot it sags in power then you are starting to enfore pre mature wear but running an engine hot and happy will allow it to last longer ...

The happy part relies completely on the quality of the oil you use

Cheers MM

MM