This item is the tuned, or megaphone, type exhaust tube to up-power a Johnson 9.9 built 1974 thru 1992 to 15 HP. OMC introduced this on 1981 15 HP models to improve exhaust scavenging to get a full rated 15 ponies at the prop shaft.  IOW, you actually need this if you have a 1974 thru 1980 Johnson or Evinrude "15" model, too.  Thanks for looking.