exhaust manifold water injection

gentlemen
need assistance regarding ways to prevent water injection on a mercruiser exhaust manifold
454 7.4 1996
any advice will be appreciated

What's your exhaust configuration? Straight out and down would not be preferred. From riser to lift bucket then up over and down would be preferred!

Do you mean “water reversion”?

Not much to go on but not turning the key to off with forward motion helps .

There is a history of water ingestion, reversion, whatever you want to call it. The basic problem is water can under certain conditions enter the engine through the exhaust. There are two basic problems here that cause this and they boat are very much related to the specific boat and exhaust system design:

1. The exhaust system design - there is not enough "rise" in the exhaust system as it exits the engine and based on the design of the boat and the engines relation to the water line, it's possible for water to come back through the exhaust and enter the engine. Older inboard engines with "log" style exhaust systems vs the newer "lift" type mufflers are more prone to this issue.

2. On GM 7.4 liter engines the valve design or "overlap" (the period where the exhaust and intake valves are both open to some degree) can create a negative pressure situation in the exhaust causing water (really water vapor) to be drawn back into the engine. This usually occurs at low/idle speeds and manifests itself over time with rusty valves. Salt water boats are more prone to this issue. I would say if a boat has these engines and has more than a few hundred hours on it, it's not likely to have the problem.

I'm not an expert on this and have never had the problem, just aware of it.
Google Mercruiser Engine Water Ingestion and you will fine tons of information.

If you are referring to your 400? The mufflers should stop any water from the outside of the boat finding it's way to the exhaust. The real issue is the center upward riser, while the manifold it self is fresh water cooled (anti-freeze) the riser has salt water in it. When you shut the engine down, no matter moving or not, salt water will always sit in the riser. This eats away at the thin wall and eventually erodes and leaks into the exhaust corroding the exhaust valves, head and more importantly the cylinder ways. Usually only cylinders 3,4,5 and 6 are most at risk. I have seen a hydro-static lock up if the problem goes for too long and the boat sits for an extended period of time. Over time even if there are no signs of an issue, it can leak back into the cylinder and over time destroy your engine causing the need to rebuild or have to replace the block.

The only way to avoid this is to replace the risers every couple of years. Check and replace the gaskets every year. It's just a poor design. The after market risers are not the same as factory, and yes even if you get them from the dealer in most cases they are still after market. Not everywhere and there are good dealers that go the extra step to get factory parts but not many.

Thank you guys
My mechanic advised me to replace all 4 exhaust manifolds and elbows with a dry set from Mercruisers to avoid water ingestion
Over 4500 in parts
It’s just I don’t drive my boat often
Just idle and once a while get on plain
I use it to sit and relax by ocean