Ed,
Is there any consensus at this time as to which alloy (304 or 409) is the most
durable for our hot breathed 13B rotarys ??
--
Kelly Troyer
"Dyke Delta"_13B ROTARY Engine
"RWS"_RD1C/EC2/EM2
"Mistral"_Backplate/Oil Manifold
Kelly,
I'm not Ed but I did sleep at a Holiday Inn Express!!
Alloys to use for Rotary engine exhaust in order of decreasing desirability (and cost)
1.) Inconel
2.) 321 Stainless
3.) 304 Stainless
4.) 409 Stainless
5.) Mild steel
Basically 409 is a low chromium stainless designed for the automotive market, specifically for exhaust tubing. It does not polish well and will develop a protective coating of rust. It will live just fine, but will be less attractive.
If you move up in cost you get a higher chromium and nickel content and therefore a higher temp resistance and creep resistance. This means you can make everything lighter and thinner. Of course it becomes much more important to properly design the manifold for expansion/thermal cycling loads the thinner it gets. So you will have to put a lot of slip joints and metal bellows in it to seal it up if it is a turbo installation. So.....how much do you want to spend to save 5 lbs or have a polished tail pipe is the question.
Mild steel will work fine if it is thick enough. Especially if you coat it with ceramic. I suppose you could also coat the 409 stainless with ceramic if you want a nice finish, but it might be less expensive to just use 304 at that point.
Monty