STOCK MOTOR GEARING
There are two motor tuners that race at my home track. David Gullikson, owner of AXIOM motors and Dennis Anderson, owner of Birdman motors. They've both told me that when you gear a stock motor:
"don't worry about heat, they're going to get hot...gear them so that you're maxing out before the end of the straight and leave it. As long as you're not getting soft before the end of the race, heat doesn't matter." I gear on the same teachings and my motors run awesome. Its true though, as long as you're not getting soft before 5 minutes is up, don't worry about the heat. Besides, I'm sure your track has an air compressor that you can use. Just walk over there and air off you motor for a few minutes and its good as new.