The key is that the valve needs to be overcome by the exhaust gasses. When the valve closes pressure builds and loads the motor. Then the valve opens and relives the pressure. It repeats this rapidly. Just make sure the 12v motor you use is not to powerful or somthing will have to give.
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97 2500 4x4 5 speed ext long box. 5" FBD Sraight. #11Fuel Plate. Star Wheel Cranked.