Mercury – Exhaust Manifold | V6 Series | Corrosion-Protected Cast Iron | 99746A17Mercury Exhaust Manifold V6 Series Corrosion Protected Cast Iron 99746A17 Overview. There are a few parts on a MerCruiser engine that you simply expect to work without drama, and the exhaust manifold is one of them. When its right, your engine breathes easy, runs cooler, and feels smooth through every throttle setting. When its wrong, you feel it instantly in the idle, in the temperature, and in your own peace of mind. Thats why boaters trust the