5 races for a pushed engine is good.. thats 5 races + the practice session.
thats about 10 hours of full throttle riding..
after that much on a high output engine, you need to AT LEAST disassemble it and check your tolerances and clean everything.
a stock 125 should do a piston/ring/pin/bearing job every 22 hours. and the Blaster is air cooled, so you cant maintain the tight tolerances you do in a water cooled 125.
ofcourse, if you have enough money, you could tune it for BIG power and get only one race out of an engine.. its all relative to what you use your engine for