It depends on the engine. I have a Sirio that runs great at 260-270 but the manufacturer says that is in the danger zone. I also have the 21BB in my daughters Savage and it likes 220-230. To get an accurate measurement take it at the glow plug inside the head. Just point the guage inside the head at the base of the glow plug closest to the exhaust port. This ensures the hottest temp. I you were to take it closest to the intake it woul be cooler since the fuel enters the combustion chamber there it cools because fuel is cool.