Good news about Permatex Ultra Copper gasket maker.
Two years ago I replaced an exhaust adapter, after I had earlier replaced the other exhaust adapter a few years earlier.
The first replacement I had not coated the inside. Had major flaking rusting so I built it back up with bronze rod. this is a steel part that joins the log exhaust manifold to the riser.
The second replacement I had coated the inside with Ultra Copper, and there is absolutely no rust at all. I cleaned off the soot and you can see the Ultra Copper still is there underneath the burnt on carbon.
The lower part of the inside pipe you can just see the Ultra copper, the baked on carbon was tough to clean and I wanted to show you that it survived inside the exhaust stream.
So I do not need to braze, I can just coat the other engines adapters and the inside end of the exhaust manifold with Ultra Copper.
Of course it could be the other two adapters on the other engine are rusted so much they will need brazing.
Link to ultra copper
Gasket Makers : Permatex® Ultra Copper® Maximum Temperature RTV Silicone Gasket Maker
Says good to 700*F. I also think that this ultra copper insulates the metal from the exhaust heat a little. And I think inside a water cooled exhaust manifold the wall temperature of the cast iron manifold exposed directly to exhaust runs cooler than in a non water cooled manifold. So I bet you could coat the entire inside surface of a water cooled manifold that is exposed to exhaust gasses and the coating would survive intact. It certainly survived the heat inside the small short adapter and there is no cooling water flow for that.
Adding pics of the exhaust riser.
It would be nice to be able to coat the inside of this riser to prevent rust. I could remove all the rust, but how could you coat it? The riser bends, I had thought of a swab on a metal stick.
See the inside exhaust surface of a riser still rusts even if it is fresh water cooled.
To left is where I brazed on a 3 inch bronze pipe 16 years ago.
That has never corroded even with hot salt water and exhaust.
Red hose injects salt water.
The other 2 pipe nipples circulate antifreeze water, the FWC part of the coolant flow.
This keeps the water passage from rusting.
Inside down the pipe view where exhaust exits. Cast iron is rusty.
Lower end where adapter attaches
Where the adapter attaches to the 50 year old FWC exhaust manifolds, a small amount of cast iron erosion was occurring, ate up half the wall thickness, only at the very end about 1/2 inch. This one I built up with bronze rod. But the other 3, I plan now to use the Permatex Ultra Copper instead to fill up the metal. First I will clean the casting. It does not have to real clean, the Permatex Ultra copper sticks regardless. Rotary wire brush is all it needs.
Entire log riser made by Palmer.