"The 4 slotted passages are th
"The 4 slotted passages are the cooling section of the Manifold (isolated from the exhaust section).
If you have fresh water cooled manifolds there is a block off plate installed before my elbows (I don't have risers).
If the manifolds are raw water cooled, there is a 2 hole gasket used (1 large middle hole for the exhaust + 1 slotted hole, positioned at the top, for the raw cooling water to flow out into the elbows.
see items 8, 14, & 17 at the link below, and read the "Tech tips page"
http://www.marineparts.com/osco/osco20.aspx"
"The 4 slotted passages are the cooling section of the Manifold (isolated from the exhaust section).
If you have fresh water cooled manifolds there is a block off plate installed before my elbows (I don't have risers).
If the manifolds are raw water cooled, there is a 2 hole gasket used (1 large middle hole for the exhaust + 1 slotted hole, positioned at the top, for the raw cooling water to flow out into the elbows.
see items 8, 14, & 17 at the link below, and read the "Tech tips page"
http://www.marineparts.com/osco/osco20.aspx"