GM Big Block Exhaust Manifold Gasket Set | Sierra 18-4348Gasket kit includes 2 manifold to head gaskets & 2 center rise elbow restrictor gaskets for a pair of Mercruiser 7. 4L & 8. 2L center rise exhaust manifolds. GM Big Block Exhaust Manifold Gasket Set Sierra 18 4348 Mercruiser exhaust manifold gasket set For GM 454 and 502 cu. in. marine engines with Mercruiser center rise elbows risers Includes 2 manifold gaskets P N 18 0418 and 2 riser gaskets P N 18 0897