I had the mx porting from Sandtrix done on a spare cylinder, Weisco piston stk bore, ESR coolhead, 38AS carb, V-Force reed cage, ESR TRX5 pipe, FMF Turbine-core silencer (I need the spark arrestor) 14/39 gearing, Uni filter with stock airbox/snorkle.

The powerband is very explosive, it's soft on the bottom (off the pipe) but is very strong on the pipe for a stock bore engine. I would think it would be a handful to race mx but it's a blast in the sand or just play riding which is what I do. I had to freshen up the clutch to get the power down in the higher gears. This porting with a powervalve would be awesome, the low end would be better.

 

talk to bubba297 he does all kinds of porting and he got a 250r of his own