Only advantage to aluminum that I can think of is weight. Cast iron
certainly lasts a good long time even in sea water. Risers are a whole
other thing.

If I was going to replace manifolds on an inboard engine I'd go with
stainless but only if my intention was to keep the boat for many more years
for some kind of payback.

The stainless guys claim some performance advantage???

Butch
"N.L. Eckert" wrote in message
...
Colonel wrote:
I've been considering using aluminum exhaust manifolds with zinc anodes,
but everyone I talk to says don't do it. It seems to me that outboard
motors are made of aluminum and THEY don't rot out like cast iron (so
long as they have active zinc anodes) so what's the problem? My engine
runs cool â?" normal operating temp is 140° F â?" so it's
not like I'm going to have salt "baking onto" the insides of the
manifolds, and anyway, I flush the motor with freshwater after every
use. (Boat lives on a trailer.)
What do you folks think? Are the aluminum manifolds and risers (about
$100 more than the iron ones) worth a try? Has anyone here ever used
aluminum manifolds and risers on a raw-water-cooled inboard?
==================================
My first inboard was a 1959 25 ft Chris with a 283 Chev. engine. Chris
Craft was using aluminum exhaust manifolds back then. I had less than
200 hours on the engine when the manifolds had to be be replaced. They
had both burned thru at the rear of the engine. I had a friend with the
1960 version of the boat and his burned thru, too. If you were the
original owner of the boat, Chris Craft would replace the manifolds at
no cost with cast iron. I wasn't the first owner so had to buy the
manifolds, I don't recall the price but in 1965, they weren't that
expensive.
Also, it should be noted that I'm in the Great Lakes, so these boats
only saw fresh water, I can imagine what it would be like in salt.. My
advice would be to stay away from aluminum (if indeed, they're still
available), but Stainless would probably be a different story, but
$$$$$ I'm sure.

Good luck, Norm