This manifold has a center riser and fits either side of the engine. For replacement of Mercruiser V6 Manifolds with center risers. Mercruiser Part # 99746A8. Sierra Part # 18-1952. Applications: • Engine: 175, 205, 4.3L, 4.3LX (Serial # B527955 and up)• Engine: 4.3L, 4.3LX (Serial # D714107 and up)• Engine: 4.3L, 4.3LX (Serial # F000878 and up)• Engine: 185, 205 (Serial # A331455 and up)• Engine: 185 (Serial # 6330183 and up) Fits either side of the engine Mercruiser Part # 99746A8 Sierra Part # 18-1952 | Mercruiser V6 Manifold With Center Riser