I guess I dont follow the raising and lowering the powerband by re-fabbing the exhaust. <SOME SNIPPED>
Two strokes are highly dependent on the exhaust to make their power.
The exhaust pipe is a highly tuned resonance chamber that when in tune will triple the power of the engine.
Ruin that tune, and you will cut your power to a fraction of what the stock YZ engine makes.
The length of the pipe is one of the factors in achieving a state of tune (also tapers, volumes and tailpipe/stinger diameter).
Longer = lower rpm, shorter = higher rpm. Of course where the length is added or removed is important too.
RPM is a factor in building horsepower, so shortening the pipe very slightly like YZOtis did has the potential to make slightly more rpm and HP.
My particular engine (2003 KTM250SX) has a reputation for strong but peaky power. Lengthening out the pipe helped smooth that out.
MX engines offer huge hp gains, a typical 250 makes 40-50hp in stock form.
The largest problem with most of them is very limited transmission gear range.
A 300 lb (very light by quad standards) Blaster needs more 1st gear ratio to get moving than a 200 lbs limited traction motorcycle. The overall gear spread on a Blaster transmission is in the range of 6:1, most MX are only about 2.5:1 and even wide geared enduros are only 3.25:1. My KTM Blaster has a too tall 1st gear, and yet top gear is out of rpm at 65mph, even though a change of sprocketing could show you much faster due to this gearing.
Everything in life is a compromise. An MX powered Blaster is no exception.
Tall 1st gear makes technical trails and rock climbing difficult.
Limited top speed makes safety sense, but is annoying to have more sluggish quads inch by you on long flats.
Hillclimbs, wheelies and acceleration are its forte. Hugely fun.
Steve