Includes titanium top collars, steel lower collars, valve springs and a valve key set. Machining required to lower the valve guide to avoid interference with the top collar. Special 3-spring design with interference fit to reduce harmonics and control spring surge. Springs have more pressure than stock. Pressure: 180lbs - 1.600" / 365lbs -1.100" / 415lbs - .950". Coil bind: .850"