Exhaust Manifolds: Cast Iron v. Aluminum for Salt Water

[SeaNugget]

Boat is a '05 VLX with a 340 Monsoon with 1,300 hours (last 300 hrs in salt water). I think I need new exhaust manifolds based on taking off the manifolds and seeing salt water leaking out of one of the cylinders and corrosion on the exhaust valve (see links below for pics). I was considering buying cast iron manifolds , was wondering if anyone had experience with or knew if aluminum or cast iron worked better with salt water.

Corroded Valve:

https://photos.app.goo.gl/wMRVeiW2itTveReR6

Opposite side of the Block:

https://photos.app.goo.gl/bV7rs3tXX4bWT9WN9

[martinarcher]

Check out Stainless Marine.  I went with their manifolds even though I'm running in freshwater.  I had my cast iron manifold on the port side crack. 

A failure is the boat asking for an upgrade right?    

[Woodski]

When going aluminum you should include zinc anodes as a sacrificial element in the system.  I would check with the manifold vendor on sea water compatibility.  Also, run a 140 degree thermostat to keep the salt from crystallizing.

[SeaNugget]

Do you guys think the additional cost for the stainless exhaust is worth it? Do they really last forever or will they eventually corrode out? 

I looked into some options for replacements. Michiganmotors has a set of the cast iron heads for $800 although I know I would lose some power. It's $1700 for a pair of the original EXT non-cat aluminum exhaust. Or it jumps up to ~$2,400 for the stainless. Piece of mind is always worth it but it seems like a considerable cost difference if it's only an extra few years of life. 

I flush religiously with salt-away and drain the manifolds after every outing in casing anyone was wondering. Wasn't enough to prevent them from corroding although perhaps the anodes would have helped.  

I ran a 143 degree thermostat this year after seeing that suggestion in another thread, but then I also read that the computer wont run right if it's not up to the 160 degree temp it wants to be at. It smelled like it was running rich this year, but that could have been contributed to the valves not sealing consistently. 

 

[Eagleboy99]

In saltwater?  I'd go stainless.  Like Dad used to say "Buy once - cry once">  I think htey have 5 year warranty?

[Slayer]

IIWM, I'd go stainless as well.