In order to run the higher lift VVT 5.7L and 6.4L HEMI camshafts, you will need to upgrade your stock valve springs. This package comes with everything needed to plug-n-play the valve spring upgrade on VVT cylinder heads. Contains: PSI LS1515ML Valve Springs, Manley 23629-16 Retainers and (6.4L required shims) 24 shims in total: 1 Thick Shim & 1 Thin Shim on Intake, 1 Thick Shim on Exhaust (no shims required for 5.7). Installed height is 1.950". Contact HHP for more information.