[71 super]

On trucks without- especially with clutch fan there is actually blow through -for lack of a better term- that is felt into the cab from the engine compartment. These seals prevent that from happening as well as the dirt/debris issue. I think that the seals may have been part of the comfort/convience option like the under dash insulation found in the higher end trucks. All adds to the reduction of noise and increases the comfort level- aiding in the move from utilitarian to the modern comfort these trucks helped Chevy move toward. They require the special brackets as stated earlier that are not repoped. The seals come with thick/heavy staples that hold them onto the sheet metal bracket. I jave yet to be able to use the staples that are sent with these and instead use a heavy insulation staple from Lowes. They require 14 or so staples per bracket and I install them by inserting and then bending with a punch. You must have the brackets for the seals to install correctly and there is a specific bracket for each side. They simply install with a couple of screws into the cowl region as pictured in the build manual schematic. Hardest part are the staples.