I have a couple of quick questions,
1. Is it an infra red thermometer designed to be used with RC engines?
2. Have you check it againist any other thermometers? You can always compare it to other thermometers at the track or maybe your friends have one.
3. Why don't you use a thermocouple? It is probably more repeatable, you can record highest temperatures reached and it is cheeper.
Dishy