DIY Tubular turbo exhaust manifold

[Mr Peepers]

I've been wanting to do this since my first cracked exhaust manifold(1g? really?) on my first DSM. I've been looking into this for a while but have had limited success on tips for making my own. My original plan was to make up a jig for the stock manifold so the tubular one put the turbo in the same location, but after talking to someone for tips, and accepting my addiction, I'm going to move it away from the block ~1" to allow for a larger turbo down the road. I won't be using the stock oil/coolant lines anyway and by having it farther from the ports, it'll make the bends smoother and allow more room for designing. All pluses.
I can get scrap mild steel easily and have a decent MIG welder to mess around with some designs before it's put through its real world testing. I don't mind the practice.

This is to mate a 7cm Mitsu turbine housing. The manifold itself will not be flanged for an external wastegate.

In the end I want to end up with a full stainless steel tubular mani with 1/2" flanges and stainless U bend tubing, preferably all TIG welded by yours truely(who has yet to touch a TIG).
My main concerns are:

1. Flow- as long as the bends are smooth and the collector is well designed(love this simple design but space may not allow http://store.straightlinespecialties.com//product_info.php?products_id=256) I shouldn't have a problem with it being better than most cast. If possible, equal length(more or less).

2. Durability- If it cracks eventually, not out too much besides some time and a little money, but gaining a lot of experience.

3. Ease of install- as long as it's physically possible to get all the bolts/nuts tightened down I think I can forgive myself. Must not interfere with any other components.

There is a divider on stock manifolds, that splits cylinders 1,4 and 2,3. This pattern is the same with many aftermarket/custom tubular manifolds for 4g63t's, with the primaries 1,4 merging into a secondary and the same with primary runners 2,3. Will this have much affect with a non divided Mitsu turbine housing? Should I bother with a plate separating the two in the collector? On the stocker it seems reducing turbulence was its main purpose.
What stainless steel should I use?
Will 1-1/2" diameter piping match the circumference of the stock exhaust ports when the ends are made into an oval?
Is .125" thick piping preferable? (1/8")
JetHot/ceramic coating? Will the thermal expansion of stainless steel cause a coating to crack?
Any foreseeable problems?
Order of assembly so you can weld everything properly?
Placement of extra support if needed?

I have plenty of time before my car is up and running again, and even if it never turns out, I'll know what not to do. Maybe someone else can benefit from this thread too. I love messing with stuff like this.

Any tips are much appreciated.
Thanks,

-Matt

 

[Mr Peepers]

The exhaust ports are ~1-1/4" tall and 2" wide. So no, 1-1/2" pipe will not work, but a pipe 1-3/4" ID will be just the right size to match the ports. Seemed like most tubular manifolds were 1-1/2" runners


1-3/4" OD pipe, shaped to the port, fits inside near perfect.

 

[dsm-onster]

Good to know about that pipe diameter there. Keep posting your progression and just build. I'm interested in doing this too.

I'm wanting to build a t3 flanged header topmount for an hx35. Topmounting the turbo may help w/ clearance issues associated w/ those big compressor housings.

 

[Mr Peepers]

Reminds me of another question.

Where would the ideal turbo location be? Where would you move it from the stock location, even if it was just a small amount? Looking for opinions on what people would change if they could.

 

[staticbrainwash]

Sticking out the front of the car shep style!

 

[Boosted98gsx]

Make sure you do some stress tests on different material thicknesses. Also I believe 304 or 321 stainless is a good stainless to use for a turbo manifold.

 

[Mr Peepers]

Anyone who didn't know about these grades of stainless(myself included) and was curious:

304 stainless info: http://www.azom.com/Details.asp?ArticleID=965

321 stainless info: http://www.azom.com/details.asp?ArticleID=967

321 has higher hot strength than 304, but is not as readily available. -from articles above

Most high end tubular manifolds are made from either grade, including Shep's with 321(haha, Geoff)

 

[Boosted98gsx]

Good info. Let us know how the wall thicknesses play out.

 

[staticbrainwash]

I maintain that for practice you should still make me a 2.5" tubular o2, haha.

Personally, it's probably a bit more expensive, but I'd go 321. Especially with a higher hot strength, it IS a manifold after all.

I am also curious about wall thicknesses though. Are you going to build a bracket for the turbo or exhaust, or make the manifold strong enough on it's own to support the weight?

 

[Mr Peepers]

I maintain that for practice you should still make me a 2.5" tubular o2, haha.

Personally, it's probably a bit more expensive, but I'd go 321. Especially with a higher hot strength, it IS a manifold after all.

I am also curious about wall thicknesses though. Are you going to build a bracket for the turbo or exhaust, or make the manifold strong enough on it's own to support the weight?

Ha, send me the materials and a TIG, it'll be covered up by your lower heat shield anyway

I will probably end up bracing it even if it's strong enough by itself, and giving the manifold some triangulation. Sadly, I won't be tucking it behind my front bumper, so a bracket between the flange and collector should suffice

 

[sophat34]

if you need help with the tig welding part shoot me a pm. i am north of madison about 20 min. I am pretty good with a tig welder, i just dont have a band saw or i would have already given this a shot.

 

[snox135]

If you have any questions about the TIG welding shoot me a pm. I'm in J-ville as well. I've been doing stainless fabrication for years.

 

[Mr Peepers]

Thanks snox135! I thought I recognized your screenname Weird how stuff like that happens.

 

[GVR4592]

Reminds me of another question.

Where would the ideal turbo location be? Where would you move it from the stock location, even if it was just a small amount? Looking for opinions on what people would change if they could.

I think moving it away from the block and slightly toward the passenger side of the vehicle would be optimal. You'd have more clearance for a larger compressor housing, and room for a larger O2 housing, as well as having more motor mount clearance for the oil return line.

 

[blcknspo0ln]

I think moving it away from the block and slightly toward the passenger side of the vehicle would be optimal. You'd have more clearance for a larger compressor housing, and room for a larger O2 housing, as well as having more motor mount clearance for the oil return line.

Well, another thing to consider is on a stock manifold and a down firing turbo, the exit of the comp housing points straight (or nearly to) the front motor mount. Moving it to the pass. side would place the exit right over the motor mount. The obvious remedy is to get a 90* elbow and weld it. Other than that, you're definitely right in that suggestion!

 

[blcknspo0ln]

You must be logged in to view this image or video.

That's with a to4e comp housing, stock 2g manifold, and the motor mount. As you can kind of see, the outlet is about 1-1.5" more towards the driver's side of the motor mount and if you move the manifold location over towards the passenger side, it, in essence, will place the outlet right on top of the motor mount. Again, if you weld an elbow on, you're golden.

 

[Mr Peepers]

Moving it to the pass. side would place the exit right over the manifold.

This is what I didn't quite get. By manifold did you mean motor mount?

 

[Boosted98gsx]

If you have a front mount, why would you want the comp outlet on the passenger side of the front motor mount anyway?

 

[blcknspo0ln]

I get it now, yes, I meant "the motor mount". As for why wouldn't you, you would, i'm just being captain obvious.

 

[GVR4592]

Is that picture from a 1g or a 2g?

 

[blcknspo0ln]

my old 2g talon fwd

 

[absolute_DSM]

I would employ the help of snox and sophat, TIG welding takes some practice but helps if you have some people to help push you in the right direction.

And if you want to build a good manifold, just email SSautochrome on ebaymotors about how to build one. Then do everything OPPOSITE and youll have a badass manifold.

 

[tkelly27]

With walls that thick I'm not of the impression it matters what type of SS you use. If it's the same stuff I'm thinking of, .125" walls can be made with mild steel and still be happy. Whatever you use, brace it. It really doesn't matter what the hot strength is if it's not supporting any weight.

If you want to save some $$ and make your own collector, this is pretty cool
http://www.theturboforums.com/smf/index.php?topic=65147.0

 

[Mr Peepers]

^That is a good idea. Ingenuity ftw

I'm having trouble finding anything even .100" in 321 stainless. Even the thin stuff is ridiculously expensive. I would be willing to say roll cage thickness mild steel would hold up just about as well as the stainless I'm finding, especially if it's braced. I'm also wondering if it would be best to tackle a mild steel one and see how it goes, then if/when it cracks, go with stainless and have some experience. Then know how much stainless I'd need, and be able to change little things that were wrong with the first.

By the way, I plan on making everything myself, maybe with the help of a generous local machinist.

 

[tkelly27]

Stainless is such a pain in the ass to machine (especially at those thicknesses), weld, and the cost of flanges that it might be in your best interest to start with mild. You can get schedule 40 straight pipe from home depot, and 90* bends from your local steamfitters. Up here in Portland it's like $4-5 for a 1.5" (it's like 1.6xx", same as mcmaster) 90 short radius, and no stupid shipping costs!

Also, I asked the dude, and SS bends are only $1-$2 more! I made a log manifold, it's kinda cool, but next is tubular out of mild steel, then maybe someday I'll tackle the SS. Did I mention SS is a bi*** to weld? It is. : D