Aluminum vs Cast Iron Exhaust Life (e.g., Revolution Marine)?

[RedDog]

The aluminum Revolution manifolds and risers seem to be one of the better values out there. Can someone in the know share some knowledge or speculation on the durability of the aluminum if they see salt occasionally (a time or 2 per year) vs never (assuming good flushing after the occasional saft use)? How does the service life of aluminum systems like the Revolutions compare to the cast iron of stock Mercs?

[MOP]

This came up last season, I worked exclusively on salt boats for many years. Very few of my clients had ran aluminum, but those that did lasted longer than cast iron. Many get put off by intake manifolds rotting, they are sand cast made of the cheapest alloy available. Look at it this way, your Y pipes and connectors are aluminum, out drives and props are aluminum. It is the type of aluminum that is the key to its lasting. I have met many guys that worked Alaskan trawlers over the years, most of the boats are aluminum and not painted top sides. Another really good example of the durability of aluminum is the PBY an amphibian patrol aircraft used during WWII, being an EX aircraft tin knocker I saw a few when I was stationed at Eglin AFB and did speak with guys that worked on them. As long as water did not get trapped between the seams they had little trouble with corrosion, there are still a few around today. Not bad for a plane built in the late 30's and early 40's. If you want to take another step to protect the entire mass IE: all the metal parts make up a Zinc kit and insert it in the intake water hose and ground it to the block, this will help to protect everything. The kit is made using a brass T, on the straight through use the size of your intake hose, the T side got to 2-1/2 inch. Buy a reducer to 3/4 this will accept a fairly large zinc. Use pipe dope not Teflon to assemble assuring good continuity. Drill and tap the reducer for a #10 screw to be able to attach the grounding wire and ground to the block. I did this on my favored customers boats, it extended the life of cast iron manifolds and risers by about 2 years. If you are running a brass seas water stainer the cap can be drilled and tapped to accept a zinc. Electrolysis is more of an enemy than corrosion, this is especially true when water is in motion. When water is moving by a metal object the electrolyte is constantly being changed increasing the damage. You boat has much more damage underway than at rest. Mercury Marine has had a bad time with intake manifolds rotting through those that have seen it know it is right where the most water flow is present. But put a zinc in the passage and it is greatly reduced.

[JimG]

I'd run aluminum in a heartbeat! Just flush 'em good and they'll last a long time. See this post:

http://www.donzi.net/forums/showthread.php?t=25108

[RedDog]

Thanks Jim - thats the answer I was looking for