The Crosman Power Pack is marketed as an essential upgrade kit for the Crosman 2240, 2250 and 2260 models.
 

Both pieces are available separately, too. Power Valve | Power Spring
 

Power Valve: These valves are professionally altered to deliver maximum CO₂ flow per shot.
 

They feature such enhancements as an angled exhaust port, thinner walls and less cap threads (for a larger CO2 reservoir).
 

Power Hammer Spring: The hammer spring is longer and stronger, allowing more force delivered to the hammer (and thusly to the valve) per shot.