XRAY - Model racing cars

Hello everyone,,
I have super awesome XB4 it is very beautifull,well made model and i like it more than rest of my auto's, but i can't resolve one problem and hope you can help me Here's the situation - this year i'm racing in beginner class. Here we are allowed to use three motors - LRP S10 blast (20500rpm), LRP S10 twister (23500rpm) and thrust eco 21 (25500rpm). I've tried all of them, but no matter what i'm having SERIOUS heat problems - after 5 min run all motors are well beyond 110 degrees (celsius), and after 7 minute final runs S10 reaches 150 on brushes and thrust eco just melts inside.....I've tried different gearing - 81T spur with 25T pinion. Also 74T spur with 25T and 27T - last combo (74/27) is somewhat competitive in terms of speed, but motors are smoking after first qualification. The only gearing that keeps temps reasonable (by that i mean ~80 degrees) is 74/22, but in this gearing i loose waaay too much speed - all the LRP blast models are faster in straight lines and what i gain in perfecting my turns, i keep loosing in straights. We are running big tracks (indoor clay and outdoor clay/sand) initially made for 1/8 nitro buggy, so straights are long enough to loose 1-2 positions each time. I was starting to think XB4 is not made for beginner race (i know, it's mod), but guy in same class races kyosho and his temps are normal, so i know i'm doing something wrong myself.
Any ideas would be appreciated.