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DIY 2.5" ---> 3" Downpipe w/Cat + 3" catback build

 
Old 07-05-2017, 03:29 PM
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Default DIY 2.5" ---> 3" Downpipe w/Cat + 3" catback build

Just thought I would post some of the progress I have made on fabricating a full 2.5 to 3 inch exhaust for my turbo build. You all inspired me to go out and build my own so I bought an Alphatig 200X and went to town.
Only one image for now, but I will update as I go. This picture is of the 2.5 inch inlet side vband of the 2 stage cat I bought from amazon
https://www.amazon.com/gp/product/B01N41NJIP/ref=oh_aui_detailpage_o05_s02?ie=UTF8&psc=1 https://www.amazon.com/gp/product/B01N41NJIP/ref=oh_aui_detailpage_o05_s02?ie=UTF8&psc=1

Feel free to tell me how ugly the welds are.
Attached Thumbnails DIY 2.5" ---> 3" Downpipe w/Cat + 3" catback build-img_20170702_171759.jpg  
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Old 07-05-2017, 04:08 PM
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Go look at the first page of my MKTurbo for sale thread. Copy my exhaust exactly. Win at life.

Wear good welding gear when under the car and trying to tack things together. TIG welding upside down to tack is absolutely horrible, you need 3 or 4 hands at any point in time. Use additional jack stands and jacks to help hold things in place while you are figuring out fitment. Buy the huge magnaflow muffler, the part number is in my FAQ. Build a 4th exhaust hanger for it to even it out. Get all your pipes from Mandrel Bending Solutions in Maryland, or Columbia River Mandrel Bends in Colorado. Bother have great prices and fast shipping.
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Old 07-05-2017, 04:24 PM
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Things I learned about welding V bands.... they warp. Really really bad if you aren't careful. What is beautiful now, will look like a tulip in 5 minutes. So, how to avail this?

1. Tons of short beads runs. I think I count about 6-10 beads at a time.
2. Alternate 180 each bead set. Cool as needed to keep it not-hot. I went so far as to wiring a wet sponge in place. It helps cool things and let's you know when things are getting hot.
3. Avoid having to run back over to smooth things out with the torch. This usually causes more harm than good on a V band.
4. Check with a straight edge when you are done. This is when you get to know if it's junk or not.
5. Buy a bunch of extra everything when you are learning to weld.
6. DO NOT TRY TO WELD WITH DIRTY TUNGSTEN. Especially when you are learning. The last thing you need while learning, is an unsteady and u predictable arc column. Sharpen like 5 tungsten on both ends, change them the second you spit contamination on one.

Filler- your weld looks like it needs more. Overall, it looks like it got REALLY hot.. use the pedal, thays why you have one. Back off when you don't need the heat. stand on it to melt in the rod, ten back off.

This is all just my own practice, others might do it different. I am extremely particular about how my fab work looks and performs, and this is what works for me.
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Old 07-05-2017, 04:36 PM
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Originally Posted by ryansmoneypit View Post
Things I learned about welding V bands.... they warp. Really really bad if you aren't careful. What is beautiful now, will look like a tulip in 5 minutes. So, how to avail this?

1. Tons of short beads runs. I think I count about 6-10 beads at a time.
2. Alternate 180 each bead set. Cool as needed to keep it not-hot. I went so far as to wiring a wet sponge in place. It helps cool things and let's you know when things are getting hot.
3. Avoid having to run back over to smooth things out with the torch. This usually causes more harm than good on a V band.
4. Check with a straight edge when you are done. This is when you get to know if it's junk or not.
5. Buy a bunch of extra everything when you are learning to weld.
6. DO NOT TRY TO WELD WITH DIRTY TUNGSTEN. Especially when you are learning. The last thing you need while learning, is an unsteady and u predictable arc column. Sharpen like 5 tungsten on both ends, change them the second you spit contamination on one.

Filler- your weld looks like it needs more. Overall, it looks like it got REALLY hot.. use the pedal, thays why you have one. Back off when you don't need the heat. stand on it to melt in the rod, ten back off.

This is all just my own practice, others might do it different. I am extremely particular about how my fab work looks and performs, and this is what works for me.

I like the v-band assemblies from MBS out of all the ones I have found because the collar part of the flange is longer then most other brands. Whenever I am welding a v-band flange on I always have it clamped to another flange that is welded to a another pipe. This way the heat has more places to move, and it does a much better job at keeping the flange straight.
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Old 07-05-2017, 04:57 PM
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Cool beans. As long as it doesn't leak. At least you are learning. And if your welds are ugly, but don't leak, and still hold, and you've got mad grinder skills, who am I to argue?
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Old 07-05-2017, 05:00 PM
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Originally Posted by shuiend View Post
I like the v-band assemblies from MBS out of all the ones I have found because the collar part of the flange is longer then most other brands. Whenever I am welding a v-band flange on I always have it clamped to another flange that is welded to a another pipe. This way the heat has more places to move, and it does a much better job at keeping the flange straight.
excellent idea. I'm going to steal that one from you, and go make one now. Thinking about it now, I think I might turn one from aluminum or brass. Just like my heat sinks for welding spherical bearing cups. Damn I feel like an idiot for not thinking of this before! You has the smart.
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Old 07-05-2017, 05:09 PM
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I have the alpha tig 200x as well and this is what my vbands look like. The vband is 3" stainless and the cheapest one I could find on eBay that came with a stainless connector. The exhaust is aluminized. After tacking I got away with 4-5 beads. I didn't notice any warping. I just placed it on the end of the pipe and lined it up straight and went to town. Where does everyone else source their vbands?
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Old 07-05-2017, 05:16 PM
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Would welding stainless exhaust to stainless vband make a huge difference to warpage vs aluminized exhaust to stainless vband?
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Old 07-05-2017, 05:32 PM
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Originally Posted by Joseph Conley View Post
Would welding stainless exhaust to stainless vband make a huge difference to warpage vs aluminized exhaust to stainless vband?
Not enough to matter on an exhaust for a miata. All my exhausts are aluminized while all the v-band flanges I use are stainless.
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Old 07-05-2017, 05:55 PM
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LOL that was quick. I have been graced by the presence of god emperor shuiend himself.

And yeah, I think the weld was too hot, but it definitely penetrated, if a little undercut. Another thing that sucked was the fact that there was this huge thick blanket of white residue and oxidation that developed on the both the outside and inside of the weld, but mostly on the inside. I looked it up to see if it was because I was welding galvanized metal, but the guys on welding forums never post pictures for some reason, so I don't have a visual comparison. It was completely white, and had the mechanical properties similiar a very very thin sheet of PTFE or something. It also broke apart and floated in the air easily. I'm not dead yet and this was 2 days ago. Tell me what you think. I cleaned the metal very well before welding including using acetone, so it had to be a coating on the metal or something.

As for warpage, I tack about 8 tacks alternating 180 degrees from each other. I then wait about 10 mins and do the final passes. The vband is a little warped, but not enought to create a sealing problem I don't think. They are the mating kind with a machined lip and groove to center it, so that should help.

EDIT: Damn I just looked at Mandrel Bending Solutions' prices.... thanks for ruining my day. I could have saved $100 by now if I had gone through them....
I also plan to use this fancy high heat polyester tape to hold joints together for fitment and then tack it all together off of the car.
Amazon Amazon
Again we'll see if that works.

I'm also curious as to how you all mount your exhaust hangars. I've seen people weld reinforcement plates onto mufflers and tubing where the hangar is supposed to meet.
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Old 07-05-2017, 06:03 PM
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In my opinion this is a perfect place to be using silicon-bronze filler. The white is probably from te aluminum coating if you didn't sand it off.
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Old 07-05-2017, 06:21 PM
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Would silicon bronze hold up to the heat?

Also Joseph Conley, I source my vbands from Tough Turbo Parts on eBay. They are here in GA so I get them super fast. They are nice quality, but I think they are aluminized or zinc coated or something. I ordered mine in mild steel so I guess they do this to prevent rusting before they ship.

http://www.ebay.com/usr/tuffturbopar...p2047675.l2559

EDIT: Yeah they say zinc coated right in the description. I'm going to die aren't I...
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Old 07-05-2017, 06:27 PM
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Originally Posted by MHM1 View Post
LOL that was quick. I have been graced by the presence of god emperor shuiend himself.

And yeah, I think the weld was too hot, but it definitely penetrated, if a little undercut. Another thing that sucked was the fact that there was this huge thick blanket of white residue and oxidation that developed on the both the outside and inside of the weld, but mostly on the inside. I looked it up to see if it was because I was welding galvanized metal, but the guys on welding forums never post pictures for some reason, so I don't have a visual comparison. It was completely white, and had the mechanical properties similiar a very very thin sheet of PTFE or something. It also broke apart and floated in the air easily. I'm not dead yet and this was 2 days ago. Tell me what you think. I cleaned the metal very well before welding including using acetone, so it had to be a coating on the metal or something.

As for warpage, I tack about 8 tacks alternating 180 degrees from each other. I then wait about 10 mins and do the final passes. The vband is a little warped, but not enought to create a sealing problem I don't think. They are the mating kind with a machined lip and groove to center it, so that should help.

EDIT: Damn I just looked at Mandrel Bending Solutions' prices.... thanks for ruining my day. I could have saved $100 by now if I had gone through them....
I also plan to use this fancy high heat polyester tape to hold joints together for fitment and then tack it all together off of the car. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Again we'll see if that works.

I'm also curious as to how you all mount your exhaust hangars. I've seen people weld reinforcement plates onto mufflers and tubing where the hangar is supposed to meet.
Good luck using tape to hold things in place. I have not had much luck with it when it comes to exhaust parts.

I weld exhaust hangers straight to the pipe. I try to put a decent side bead on either side of it. As far as I am aware I have had a single one break out of 50+ exhausts. That guy things it was far more because of his crappy roads and potholes and such more then my welding.
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Old 07-05-2017, 07:15 PM
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Well the way I am going to attack it is to build the downpipe/cat section, and then hang hang and mount the muffler where I want it. This way most of the weight of the exhaust system is already held to the chassis, so the tape shouldn't have too much work to do hopefully.

I also just researched how to get rid of a zinc coating. Brb getting pool cleaner (HCl)
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Old 07-05-2017, 07:56 PM
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A quick pass around the weld are with nome sand paper should be just fine. I use the cheap stuff on a roll from harbor freight. 150 grit. 1 inch wide.
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Old 07-05-2017, 08:49 PM
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too late

EDIT: Where should I dispose of this?
Attached Thumbnails DIY 2.5" ---> 3" Downpipe w/Cat + 3" catback build-dsc_0050.jpg   DIY 2.5" ---> 3" Downpipe w/Cat + 3" catback build-dsc_0052.jpg  

Last edited by MHM1; 07-05-2017 at 10:38 PM.
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Old 07-26-2017, 04:08 PM
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Sorry for the delay, I decided to build the intercooler piping first before tackling the exhaust. Anyway, here is the downpipe. I'm running a TacoTaco T3 on a 1.8 and a Cxracing garrett T3 copy. Needless to say there was no space for the downpipe and I really didnt feel comfortable going all faeflora on my firewall shelf. This downpipe is the result.





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Old 07-26-2017, 05:06 PM
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yuk dude.

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Old 07-26-2017, 07:41 PM
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Savage


I wish I had any ability to weld. I'm at the mercy of shops charging whatever they want
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Old 07-26-2017, 08:06 PM
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Brain are you cringing at the welds or the abortion pie cut bend right after the outlet?
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