Replacing exhaust manifolds and risers - go with cast iron or aluminum?

[denhajm]

I have a '90 4.3L Mercruiser with raw water cooling (no heat exchanger) and am about to order up some new exhaust manifolds and risers to install. Boat sits on a trailer unless it is being actively used. Gets 4-8 hours of run time in salt water/year. Gets 8-14 hours/year of run time in fresh water lakes. Should I go with cast iron exhaust manifolds and risers? Why? Or should I go with aluminum ones, such as those made by HGE? If so, why?

Who has actual experience with aluminum exhaust manifolds and risers on a cast iron block from Mercruiser?

Thank you for your input!

 

[NHGuy]

Aluminum is lighter so it reduces your weight. But it corrodes faster and costs more. I'd buy anything except HGE, it's really roughly cast. Some on the forums have had to service GLM mating surfaces to get them to seal. But they at least have some directional vanes inside the manifolds to divert the exhaust gasses toward the outlets.
Mercruiser is best, but costs the most, and lasts the longest. It's probably cheapest in terms of cost of ownership over time. They also offer optional inner coated cooling passages that resist corrosion... for even more money.
Gaad boating is expensive. Thankfully I get those couple of times a year that I'm just bombing along with a big grin on my face!

 

[Rick Stephens]

I've seen aluminum exhaust take a lot of corrosion abuse in only a little bit of salt water time. I'd stick with iron unless weight is your issue.

 

[Scott Danforth]

I would suggest Mercury, Barr, or Osco manifolds. if your going to go aluminum, Kodiak, EMI, IMCO, Stainless Marine all make good aluminum manifolds that are hard anodized for the 4.3