Mercury - 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 it's right, your engine breathes easy, runs cooler, and feels smooth through every throttle setting. When it's wrong, you feel it instantly - in the idle, in the temperature, and in your own peace of mind. That's why boaters trust the 99746A17 Exhaust Manifold. It's the kind