tuning by temperature guage doesn't take into acount the ambient air temperature, which can adjust the temp of the engine. Also, I've run certain tracks that were better if the engine was a little rich, and not producing the highest power it could. You should tune to what your ears hear and what your eyes and feel tell you. I have been into airplanes for almost 20 yrs now, and I've never once used a temperature guage. It's not even a rare thing. It just doesn't happen. With cars, you can run lean easier, but you should be able to tell by the smoke trail, the sound, and the smell of the engine. Yes, the smell. I can tell when an engine is to hot by my nose, most seasoned engine tuners should be able to too.