FJ 280z Posted March 3, 2011 Share Posted March 3, 2011 so i have a guy i believe is my friend at a local tuning shop here in arizona. recently, my brother and i made a custom tubular turbo manifold for my fj20. we made the flange, and purchased an obx collector, the tubing was a 1.75" mild steel tubing i purchased at a local exhaust company. they were 180* bends, i don't remember the thickness of the pipe, but my brother being a welder said it should work. we made a pretty nice piece. it was all tig welded together. anyways, back to the tuning guy, i dropped it off to him to get decked and ceramic coated as i thought i was gonna get a good deal. he calls me this morning and says something along the lines of "oh, my fabricator guy saw it, he's worried that you made it out of mild steel, its to thin, its gonna crack all over the place, with the vibration and weight from a turbo, the coatings not gonna work for it it will only make the metal hotter and it won't last." anyways, he's wanting to make me one out of stainless, blah blah $2000 custom piece saying it will work better. am i getting bs'd here? will this manifold that i built out of exhaust mild tubing and tig welded together and jet hot coated just break apart or crack? i spent some good money on the pieces for the manifold and believe in my brothers welding, its a really nice piece as you can see in the pics. but what do you guys think? are they trying to sucker me to buy one of thier manifolds? plus, i was quoted 100 bucks for the coating, and he's saying 150 to 175. im just trying to get some hybridz members opinions so i can figure out what to do here i'd hate to have to buy new ss tubing and remake this whole thing if these guys are for real. i'm hoping someone would tell me thier full of bs and i'll take my stuff and go elsewhere. Quote Link to comment Share on other sites More sharing options...
johnc Posted March 3, 2011 Share Posted March 3, 2011 Tell the tuner thanks for his recommendations. Then ask him to do the work you asked him to. Make sure the coating you get is something like JetHot 2000 or Swain White Lightning. Ask for those coatings by name and don't accept anything that's "Just as good." Jet Hot Sterling or Extreme Sterling won't last. Quote Link to comment Share on other sites More sharing options...
Snailed Posted March 3, 2011 Share Posted March 3, 2011 Thin tubing, (~.065") either stainless or mild doesn't tend to last as long when you hang a turbo and exhasut off it, especially on 4 cyl motors. For starters, take a look at some 80's F1 turbo setups. They had thin manifolds (iconnel usually I think) and they would use a small tubular tripod to hang the turbo from it's CHRA and take the weight off the manifold. As long as the support can flex in the right directions (1/4" heims) it will do a good job of taking the stress off your manifold. I have fabricated turbo supports as elaborate as the F1 stuff and some, more simple designs and found it made a big difference in the longevity of the manifolds. Consider using a long flex joint in the downpipe and supporting your exhasut very well also. Another large factor in manifold durability, is getting clean, full penetration welds. If you have a crack or a pile of sugar at the root of the weld, inside the pipe, that is a huge stress riser and it won't really matter how think your tubing or pipe is, it will break there. As far as the coating goes, it will keep more heat in the steel and probably make it weaken faster. I guess the theory of coating the inside of the pipes is that the heat doesn't get in the metal to start but I have yet to cut into any exhasut part and find the inside properly coated. That's part of why high grade stainless is a good material for manifold, it doesn't conduct heat nearly as well as mild steel. Incidently, 304ss weld els (cast pipe weld fittings that many turbo manifolds are made from) are cheaper than mild steel ones. Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted March 4, 2011 Share Posted March 4, 2011 As noted above, the welds themselves can be a problem. Believe it or not for things that need to be tested (aerospace and defense parts), my boss finds it easier to weld stainless. Mild steel is more difficult to weld "right" then stainless because it is dirtier. Porosity in the weld is a big issue especially when TIG welding mild steel. Also, I know this is anecdotal, but I was always told to use SCH40 weld els for mild steel manifolds, SCH10 for stainless. That said coat it and run it until it breaks. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted April 23, 2011 Share Posted April 23, 2011 (edited) Mild steel expands less with heat, it apparently doesn't crack as easily as SS. I'd still build a support for the turbo. Edit: This thread was a little older than I thought, oops. Edited April 23, 2011 by letitsnow Quote Link to comment Share on other sites More sharing options...
BLOZ UP Posted April 23, 2011 Share Posted April 23, 2011 I'm making a pair for my VG30, with plans to brace the turbo. I'm using SCH10 304 butt weld fittings. I've been told by everyone, 304 is going to to crack, it won't last long. You should have used 321. My reply is usually: "Yes, it might fail with high heat. But for the price of making ONE manifold out of 321, I can make 3 out of 304." And I'm willing to bet my first complete design could use a few small "revisions" once it's all done. Quote Link to comment Share on other sites More sharing options...
johnc Posted April 23, 2011 Share Posted April 23, 2011 I'm using SCH10 304 butt weld fittings. I've been told by everyone, 304 is going to to crack, it won't last long. Well, everyone is wrong. Cracking in 304 has much more to do with the preparation and welding process then the base material. Make sure your fitup is as perfect as possible with no gaps greater then the diameter of the filler. Use 308L filler wire. Purge the inside of the tubes with 100% Argon for 5 minutes before welding and plug each end of the tube with bronze wool or a heat resistant plug. Keep the purge going while welding. Use a 1/16" thoriated tungsten and a 1/16" diameter filler wire. Keep the tungsten sharp and clean. Tack in four places evenly around the tube and run a weld bead from tack to tack without stopping (you'll need to make few dry runs for each bead to get this right before welding). Make sure the bead wets in and try to minimize the heat input while still getting good penetration. Pause at the end of each bead for about 10 seconds to let the bead cool under an Argon shield. Quote Link to comment Share on other sites More sharing options...
ozzzzz Posted April 23, 2011 Share Posted April 23, 2011 (edited) Well, everyone is wrong. Cracking in 304 has much more to do with the preparation and welding process then the base material. Make sure your fitup is as perfect as possible with no gaps greater then the diameter of the filler. Use 308L filler wire. Purge the inside of the tubes with 100% Argon for 5 minutes before welding and plug each end of the tube with bronze wool or a heat resistant plug. Keep the purge going while welding. Use a 1/16" thoriated tungsten and a 1/16" diameter filler wire. Keep the tungsten sharp and clean. Tack in four places evenly around the tube and run a weld bead from tack to tack without stopping (you'll need to make few dry runs for each bead to get this right before welding). Make sure the bead wets in and try to minimize the heat input while still getting good penetration. Pause at the end of each bead for about 10 seconds to let the bead cool under an Argon shield. Edited April 23, 2011 by ozzzzz Quote Link to comment Share on other sites More sharing options...
ozzzzz Posted April 23, 2011 Share Posted April 23, 2011 Also the cup size on the tig torch needs to be as small as posiable. It decreases the HAZ zone and chances of carbide precipitation..(Exhaust manifold for a turbo would not be an ideal first project for Stainless). Solar flux type B can also be used on the backside of the weld if backing gas is not practical.. Quote Link to comment Share on other sites More sharing options...
BLOZ UP Posted April 23, 2011 Share Posted April 23, 2011 Well, everyone is wrong. Cracking in 304 has much more to do with the preparation and welding process then the base material. Make sure your fitup is as perfect as possible with no gaps greater then the diameter of the filler. Use 308L filler wire. Purge the inside of the tubes with 100% Argon for 5 minutes before welding and plug each end of the tube with bronze wool or a heat resistant plug. Keep the purge going while welding. Use a 1/16" thoriated tungsten and a 1/16" diameter filler wire. Keep the tungsten sharp and clean. Tack in four places evenly around the tube and run a weld bead from tack to tack without stopping (you'll need to make few dry runs for each bead to get this right before welding). Make sure the bead wets in and try to minimize the heat input while still getting good penetration. Pause at the end of each bead for about 10 seconds to let the bead cool under an Argon shield. They usually are. I have a purge setup and all the correct supplies. What do you mean by "dry runs"? Are you talking about making sure I can reach continuously between tacks before starting welding? Should I let the piece cool a lot between the 1/4 circumference welds? I've heard that keeping the heat to a minimum is like #1 or #2 priority. Do I need to purge when tacking? I've heard equal amounts of "Yes" and "No" when I searched. I noticed on a few test pieces that I would get sugar if there were any gaps or if I used any filler. But tacking flush pieces without filler (.5-1.0s of arc) together nothing appeared wrong. It sure makes it a hell of a lot faster to strengthen my mock ups. Also the cup size on the tig torch needs to be as small as posiable. It decreases the HAZ zone and chances of carbide precipitation..(Exhaust manifold for a turbo would not be an ideal first project for Stainless). Solar flux type B can also be used on the backside of the weld if backing gas is not practical.. I have a medium size gas lens and cup, on a 17 air cooled torch. This is not my first stainless project, nor my first manifold project. It is my first stainless manifold though. Quote Link to comment Share on other sites More sharing options...
BLOZ UP Posted November 29, 2011 Share Posted November 29, 2011 (edited) So, to follow up... [bracing myself for any criticism...] I finished my manifolds. I was using 3/32 thoriated on one side, but switched to 1/16" and had better results. I used various sized gas lenses, finally settling on a #10 (!) with about 15CFH flow rate. I could not do continuous 90 degree beads on a lot of the joints like johnc suggested, most are 30-45 degrees. I had what seemed the least amount of heat when I did a little on each joint at a time, rather than completely welding one joint before going to the next. This also made it faster since I moved the weldment into position and then welded all the joints that I could get to. I also noticed that adding more tacks before welding greatly reduces expansion problems later on. I ended up having about 2" (!) of tungsten sticking out and 17CFH on the hard to reach areas, with as much tape and argon as I could shove in to the area. I had a couple mishaps where I didn't get enough shielding gas, but by increasing the postflow (it's a fixed amount so I have to tap the pedal to get more), I could keep the bead and the tungsten clean. I used ~10CFH pre-welding purge for one minute (or more on the larger pieces), then ~5CFH while welding. I say "~" because it's a Harbor Freight regulator and it seems to be going a lot faster than it indicates. Those low flow rates (at least) are probably inaccurate. Anywho... I made the driver's side manifold first, then the secondaries, then the passenger side. I should have done the secondaries last, duh, but refitting after the manifolds moved was not too bad, luckily. I made the driver's side collector myself, and it was a lot more work than I thought, with the tools I don't have. So, I had Adam at Columbia River make the passenger side one, and was very satisfied (only $120 bucks!). His collector was a lot smoother on the interior, among other things... Before you say it, yes, I plan on bracing the turbo with a heim joint. But I have a question, where should I place a flex joint? Do I really need one? About the only place I can see to place one is after the passenger v-band (as in, on the turbo side), where there's about 4 inches of straight. Edited November 29, 2011 by BLOZ UP Quote Link to comment Share on other sites More sharing options...
johnc Posted November 29, 2011 Share Posted November 29, 2011 Absolutely no criticism from me. Good job! A flex joint is a good idea and where you suggested placing it will work. The flex joint lets the whole assembly stress relieve itself the first few times you run the car. Quote Link to comment Share on other sites More sharing options...
BLOZ UP Posted November 29, 2011 Share Posted November 29, 2011 (edited) Absolutely no criticism from me. Good job! A flex joint is a good idea and where you suggested placing it will work. The flex joint lets the whole assembly stress relieve itself the first few times you run the car. Thanks, I'd welcome any constructive criticism, these are my first tubular manifolds. I've made only log manifolds before out of carbon steel. I will see if I can find a ~2-3/8" flex pipe. Any recommendations on cleaning out all the grinding debris from the inside? Can I just tell the machine shop to dunk it? Or spray brake cleaner/acetone all in it? Edited November 30, 2011 by BLOZ UP Quote Link to comment Share on other sites More sharing options...
FJ 280z Posted January 12, 2012 Author Share Posted January 12, 2012 wow bloz, thats some really nice work! and thanks johnc for your input. i plan on building another manifold with two wastegate tubes and a t4 flange vs. the t3 my brother made previously. great info guys, thanks again for your contributions! Quote Link to comment Share on other sites More sharing options...
sft3303 Posted January 13, 2012 Share Posted January 13, 2012 Just a heads up, you might want to read up on the actual manifold design, the first one (your fj20 manifold) is going to have pretty poor flow characteristics going towards the wastegate. The flow of the exhaust gases almost has to do a 180* turn (aka, flow reversal) to get to the wastegate, and that is something you really do not want to do (will *actively* slow your turbo while the wastegate is engaged). If anything, the path to the wastegate and turbo should ideally be separate, but equal. Aka, the exhaust comes to a "fork" in the manifold, one route to the turbo, and the other to the wastegate, where it is equally easy to go to either path. Just something to keep in mind. Quote Link to comment Share on other sites More sharing options...
BLOZ UP Posted January 17, 2014 Share Posted January 17, 2014 A follow up for my headers. They've been on the car for 2 years now, driving rarely only in the summer--mostly for autocrosses. A couple 1/4 mile track runs too. No big issues that I know of. I added a brace from the turbo to my radiator, and less importantly plumbed the wastegate back into the down pipe. There is a slight exhaust leak, but I'll look into it more when I swap the motor out. Quote Link to comment Share on other sites More sharing options...
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