Doing up an exhaust system for the 20B.

In the past I've welded mild steel to some kind of stainless and it worked ok, but I recall it was a bit touchy. 409 stainless is what I need to weld to some mild but others have said it can be tricky. I believe the stainless I welded was 409, but it could have been 304. Isn't 409 somewhat ferrous and therefore easier than 304? Has anyone here done it? Anything I need to watch out for?

Keeping it simple. Pipe size will be 3" 14 guage 409. Many thanks go to Gordon, chohakai and the venerable rotarygod.

 

Tig will be fine because you can change the electrode and filler wire to suite mild to stainless welding.

Mig not so sure.

 

Thanks. I used a flux core welder last time to join the mild to the unknown stainless. I will give it a try on the 409.

 

for mig what i have found to work best is to use overlapping spot welds and try to keep it off set so 1/3 the spot weld ends up on the stainless also make sure the spot welds overlap a little bit as well.

 

TIG it with a 309 rod and backpurge with argon if possible. If not possible use welding flux inside the pipe.

 

We weld mild to all kinds of stainless all the time. Just regular S6 wire and 75/25.

I have never had any kind of luck using flux core wire on anything. FWIW.

 

4xx series stainless is considered ferritic mainly because it is heat treatable (hardenable with proper heating and quenching) and magnetic.

3xx is non ferritic (though it still has some iron in it) and is not heat treatable and non magnetic. It will work harden from pounding or drawing but not through heating and quenching.

A magnet will direct you to the series but not the specific type in the series.

 

Thanks for the info. I tested the unknown SS with a magnet and it didn't attract so it must be a 3xx series.

I did a little reading and so far it looks like my idea to work with some 409 is probably not a very good one. I'd prefer to work with mild steel.

This exhaust system is for an NA setup. If I could find some thickwall 3" mild steel I'd prefer that over any kind of stainless. I'm getting pretty handy with a flux core welder and enjoy building systems with Racing Beat's nice 11 guage .120" wall mild steel offerings. I have grown to appreciate the way thickwall pipe keeps in a lot of the rotary noise that causes so much grief for so many NA users. The only problem is they are too small, and the 3" stuff they sell is stainless and only 16 guage. Too thin.

I did find some aluminized 3" 14 guage mild steel. A local place sells a bunch of nice stuff like U-bends, flanges and various pipe sizes and thickness. Even schedule 10 and 40. None of the schedule is quite right for me but I wonder whether 14 guage aluminized would be ok at the collector back to the presilencer. Or do I need a .120" wall thickness pipe there?

I'm not so much worried about the pipe thickness after the first muffling device, but coming right off the header will be loudest, so I assume it needs to be thickwall for this short distance. Right?

 

yes, this will work regardless if it's type 3 or 4 SS