If you pick a turbo that falls outside the efficiency range of your engine, you risk causing damage to both the turbo and the engine. It is OK for a turbo to glow every once in a while; however, you do not want it to glow continuously. If you push your turbo to operate beyond its efficiency range, you will destroy it in a short amount of time. In addition, air that has been heated to an extremely high temperature will be injected into your combustion chambers.