Re: Sound deading material. Home › Forum › Ask A Member › Sound deading material. › Re: Sound deading material. amullerReplies: 1055Topics: 163 September 12, 2018 at 3:24 pm #82720 Other question: OMC went from using basically open metal covers and inlet silencers, to sealed fiberglass hoods used as intake plenums. Are these "tuned," such that missing foam, or extra foam, effects the output? am