here you go.
Me rebuilding an SSI 14/71 hi helix retrofit blower from the tractor puller.
Mike the power valve is mean to play around with the timing on the engine so the blade has to wrap around the piston... it works via a diapfram sensing the pressure on the exhaust port after the blade... the higher the rpm the more pressure so the diaprahm lifts the blade out to higher the exhaust port.
if you did this on the exhaust outlet of the engine you would be interupting the sonic wave goming back so could make it alot worse!