Exhaust Manifold question

[Gerkin]

Hi all,
I sincerely hope I am in the correct place. If not, I apologize.

So, I have a Classic Donzi with twin screws.
The 454s fit very close to each other on the inner mounting.
The exhaust manifolds are basically garbage and I want to replace.
Because they re so close, I will most likely need to replace the inside manifolds with the same model and brand. They seem to be slightly narrower than most. (I could be wrong)

I am also trying to lose a bit of weight in the boat, so I would love to put aluminum manifolds in there.
I hope this is not an idiotic question, but Is it a big problem to install new cast iron manifolds on the inner parts of the engine and aluminum logs on the outside? In other words, each engine would have 1 cast iron and 1 aluminum.
Thanks all

 

[tpenfield]

The aluminum is going to get depleted by the iron/steel of the engine. Salt water would be no good. In fresh water, it might last a while.

 

[Gerkin]

This will be in Lake Tahoe, so it would be as fresh as it gets

 

[dubs283]

Considering overall weight of the boat installing 2 out of 4 manifolds being aluminum the weight saving is a drop in a bucket.

You'll notice zero difference and the boat will perform the same.

I have little/no experience with aluminum exhaust manifolds but if it were me I'd go with cast iron

Certainly don't envy your position regarding the inboard manifolds. If you have access to an overhead lift I'd use it

 

[kenny nunez]

Another thing about your particular set up. Hopefully your manifolds are mounted with bolts instead of studs. There are some really good aluminum manifolds available now that will hold up.
EMI and Imco are 2 examples. You never said which brand of marine engines you have.

 

[alldodge]

Had EMI on my cruiser for many years in fresh water, no issues.

 

[Gerkin]

I do agree about the weight probably will not change performance. I just know that getting those cast iron manifolds off were a nightmare and extremely heavy.
What was in there were some PCM manifolds. Held in by bolts and the heads of those bolts were rounded off. It was a fun time getting those off.

 

[Gerkin]

Nice having friends with a crane

 

[Gerkin]

 

[Scott06]

View attachment 381274

Nice having friends with a crane

Absolutely. I used the rigger I use at work, he and his son did me a solid. Took longer to set up the crane than do the lift... totally safe and easy

 

[Scott Danforth]

how many years did it sit with water in the bilge?

pic shows flywheel rusted and water line on the oil pan.

I would go with aluminum across the board or cast iron across the board or stainless across the board

Stainless Marine (aluminum manifolds and stainless elbows)
Gil Marine
Custom Marine (stainless)
Lightning Headers (stainless)
EMI (aluminum manifolds and stainless elbows
Mercruiser 8.1 liter (aluminum manifolds and stainless elbows)

Etc.

 

[Gerkin]

Thank you for that input. The boat sunk but was only down 2 days. It sunk because the person that tied up the boat in the harbor tied it to a beam instead of the floating dock. Tide went down and the boat stayed down