4 Cylinder Exhaust Manifold to Head Gasket | Sierra Exhaust 18-1204-1 Combination intake & exhaust manifold gasket fits GM 3.0L 4 cylinder marine engines with non-Vortec cylinder heads. Exhaust manifold gasket For GM 2.5L and 3.0L engines from approximately 1987 to 1990 with non-Vortec cylinder heads Will not work with all 3.0L engines - refer to engine model and serial for correct gasket Intake and exhaust ports are not square Replaces Mercury 27-96429 Replaces OMC 912164 Replaces Mallory 9-61419 Replaces Sierra 18-1204