The Crosman Power Pack is marketed as an essential upgrade kit for the Crosman 2240, 2250 and 2260 models. Also fits 2300S, 2300T, 2300KT, 2400KT 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.