Carpokes Porsche Forum

On the stock 951 the exhaust pipe between the downpipe and the catalytic converter is double walled. Apparently the inner wall is known to collapse over time / heat cycles. I learned about this after drilling a hole to install a wideband O2 sensor bung and being baffled by what I could see inside the pipe. Yesterday I finally cut the pipe in half to reveal just how bad it was.
I can't believe the car still ran as well as it did! But the performance was obviously being restricted by this, plus a number of other aged components I'm replacing. The logical thing to do here is buy an off-the-shelf aftermarket exhaust system, but why would I do that?

So naturally I bought a tig welder, some stainless pipe, and am learning as I go. At the risk of having my novice welds being ridiculed, I will share my progress and approach.
I am using 3" stainless pipe, a straight-through muffler, will include a catalytic converter, and plan to use pie cuts (or lobster cuts) to form all the bends. Not a whole lot to show yet, but here is my first bend tacked together with a reducer to connect to the original downpipe flange.
This is the last big item keeping my car off the road and summer is here, so I'm trying to get finished within a couple weeks. I'll keep updating the thread as I progress and likely make a YouTube video once I'm done. Hope to inspire or at least show what goes into something like this!

As a beginner welder. Please don’t do pie cuts. Use mandrel bends and as few joints as possible.

Also check your local community college or local argon supplier like airgas for classes. They’re cheap classes and you’ll learn a lot.

I’m still a beginner really. But good enough to build what I need.

Very cool. I bought a MIG welder maybe 20 years ago and was determined to weld my own exhaust tip on the car. Truly horrendous welds, with weld blobs on top of weld blobs. It's still on my car that way -- kind of a reminder of where I started. If anyone ridicules your welds, I'll post a picture of that and suddenly yours won't look so bad.

After using the MIG more and more I started getting the hang of it, and then maybe 10 years ago got a TIG and that's just about all I use now. I think the last time I ran the MIG was when I fixed the rusted battery tray in my car. I have a Miller Diversion TIG, which is kind of TIG for dummies, but it does everything I've asked of it. I figure it's still a way better welder than I am, so no point in upgrading unless/until I feel like it's holding me back. My only advice is to practice a lot. Those pie cuts look like good practice actually, but welding pie cuts on pipe is a kind of like learning to ride a bike on a motorcylce... I'm not in Audisports' league on the SS (nice welds!) but at this point, after lots of youtube and practice, I'm able to do the things I need.

Nice welds Tom and AudiSport. I hear you about the pie cuts not being very beginner friendly, but so far it hasn't been too bad. I figure it's good practice like Tom said. All this will be hidden under the car when I'm done so hopefully I'll have developed some skill by the time I weld something visible. Also I have a decent amount of mig and stick welding experience already. The whole idea is to have fun and I am succeeding.

I finished the seams on the first elbow tonight and am pleasantly surprised with the results so far. Only complaint is how long this is taking and how much argon I'm using.
I think I'm overheating (cooking) the stainless but haven't burned any holes yet.

Also prepared the mini catalytic converter: For the record this is 3", 14ga, 409 stainless pipe. Using 0.035" ER308L filler, with Solar Flux instead of back purging. Welder is a Primeweld TIG225ACDCP running around 40-50A.

1 elbow down, 4 or 5 to go. More updates to follow.

Do you have a foot pedal? I'd take it up to 60A . The lower Amps is and just starting out is probably causing you to move too slow putting too much heat in. But not enough to make a puddle fast enough and move on. Practice on some scrap if you can

Thanks for the tip, I'll try that. I do have a foot pedal. The machine has been set at 70A so I'm just guessing I'm running around 50A. I think you're right I could use more heat and move faster.

Where did you get the minicat? I'll need to replace my system and I'm debating cat application and source.

When I'm a bit rusty I take some scrap and just play with making a puddle and pushing it along, no filler, to get my speed and amps dialed in.

ROB III wrote: Wed May 18, 2022 5:22 am Where did you get the minicat? I'll need to replace my system and I'm debating cat application and source.

I'll admit it's a relatively cheap one off Amazon - specifically an "AUTOSAVER888 ATCC0010." Appears to be fine quality but I can't make any other endorsement yet. Ask me again in a year. I debated spending more for a brand name, high flow, cat but it is a big price jump for questionable gains. I'm not chasing peak performance on this car, it's just for fun, and almost anything will be better than the collapsed exhaust this replaces.

My wife is sensitive to smells and actually likes my Porsche, so I hope the little cat will help keep it that way.

Here are some pie cut references