large diameter automotive exhuast welding questions.

[The_Beave]

I have a bunch of questions. First, here is my current setup:

Lincoln Weldpak (the 110v unit) converted to MIG
Bottle of C25

My first question is can I use the C25 to weld .065" 304L tubing together for a car exhuast? I have been reading up on stuff, and some say it works, but there's a bit of splatter, others say it discolors the welds, etc. This leads me to think that the weds are ok, but the cosmetics aren't so wonderfull. This doesn't matter to me as the exhuast is going under the car and the only place that it matters that the welds be "pretty" are on the muffler.

Secondly, would welding that SS piping to mild steel flanges be difficult? Most shops do it, so it can't be too hard to do.

Third, I will be doing up a 3" exhuast for a turbo Honda CRX, and was wondering where a weldor would aquire a ground clamp that woud fit over 3" piping. I like to clamp the pieces I am welding right on the joint. Is this even neccessary? Can I just clamp the pipe at one end? I don't have a weding table, so please keep that in mind.

[DrIQ]

I would suggest a 400 series stainless for your exhaust project. The 300 series will probably not take the exhaust temperatures from your turbo. The C25 will not give you a good short circuit transfer and will result in a brittle weld due to carbon pickup in the 300 series.

The ground clamp can be attached to the end of the pipe, it doesn't need to be clamped on the joint

[bigolguy]

i dunno and i suck at welding but i thnk mig'n is the way to go with mifflers,tig is great to,i also seen gas welding done on muffles too

[Franz]

I don't want to deflate your baloon, but if you weld stainless to mild steel on the muffler, you will get rust that will travel down the stainless over time.

[The_Beave]

The Stainless exhaust and the 3" exhaust are two entirely different pieces. 3 series stainless is fine for the application. Thanks for the concern, though. The 3" exhuast is going to be mild steel and not expected to last more than two years.

I know what will happen with the SS/mild combination, but my freind is not willing to pay $28-35 PER flange for SS. $28 is the lowest price I've seen for a 3-bolt 2.5" center-hole SS exhuast flange. THe exhuast design isn't set in stone yet, but at least 4 SS flages would be needed. $112+shipping for flanges is a bit nuts when everything else for the exhuast including a flex pipe, new cat, etc. cost less than that.

Should I rent a bottle of 100% argon? Is it going to be that much better? The SS exhuast system isn't going to be under much stress, as there will be plenty of flexibility built in before the exhuast is actually attached to the header.

I'll just clamp the end of the pipe. Thank you for stating the obvious, DrIQ. Sometimes I miss stuff like that. heh

[DrIQ]

the mild steel flanges can be welded to the stainless with a 309 or 312 ss mig wire. Since you are looking at replacement in 2 years and have flex built into the system I would try the C25 gas.

[Roger]

Originally posted by The_Beave


I'll just clamp the end of the pipe. Thank you for stating the obvious, DrIQ. Sometimes I miss stuff like that. heh

The_ Beave is try to say It's ok to just attach ground clamp to end of exhaust pipe in answer to YOUR question. So lighten up.
I would first start tack weld on ground clamp side of joint and move bead to engine side of joint to prevent current looping through engine. Use C-clamp to electricity bridge joint and hold tubes in alignment while tacking.

If stainless steel flanges are too expensive make your own using tube, sheet and 1/8" plate. It's done all the time by those with more time than money.
I can't figure out why 4 flanges are needed anyway. If your building welded stainless steel exhaust system easiest and cheapest to weld everything and make it all stainless steel with only manifold flang.

[The_Beave]

DrIQ- I'll be testing out the C25 on the pipe soon. If I don't like the results, I'll tell my friend to pony up for a bottle of Argon.

Roger- Both exhuast systems will be fabricated off-car. The 3" mild steel system won't have any flanges at all. The tubing I am using for the down-pipe off the turbo is 3" OD. The Flex pipe and cat are both 3" ID. Those will be welded together, and then the rest of the piping will be clamped. Easy, cheap, light, and very effective.

The 2.5" stainless system is going to be installed as follows: header flanged to flexpipe welded to cat flanged to a Moroso Spiral flow muffler used as a resonator flanged the 2.5" (hopefully SS) mid-pipe flanged to the rear section. The cat is all stainless, so I'd like to put a SS flange on that side. So, one SS flange for the end of the cat, two for the mid-pipe, and one for the rear section. The reason for the pit is to facilitate some suspension work on the car, which is always being fiddled with.

Do you mean to "stack" flanges made from 1/8" plate? I am not sure how I could do that and have everything seal.

I'm sorry if I wasn't clear before. Sometimes I type too fast for my brain.

[Roger]

Flanges are sealed with gaskets.
Use High temp exhaust gasket material. If 1 gasket leaks use 2.

On tube end weld 1/8" to 3/16" wide circular flange out of same material as exhaust tube. This circular flange is narrow so higher pressure against gasket without excess bolt force. Circular flange at least 1/8" thick. Extra thickness helps keep it flat and gives clearance for it to be pushed into gasket. Weld this flange on inside of tube as weld hold better and the oval rotating bolt flange fits better. Bolt flange can be 1/8" thick but 1/4" is better. Rotating bolt flange allows parts to be aligned on car before tightening. This flange's mate can be flat bolt flange, but should use at least 1/8" (1/4" better) material to take force of bolts without bending.

Non rotating oval flanges without narrow gasket contact ring must be at least 1/4" thick.