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Old 06-12-2009, 02:23 PM   #1
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Default New Manifold?

I'm considering a new manifold, but I'm trying to decide if it's worth it.

The one I have now is home-made out of stainless (except the flange), and it keeps cracking. Apparently the guy I had weld it for me wasn't as good as he claimed. So far I've been pulling it off and having it fixed every time but that is getting old.

I have an offer from a friend who works at a very good machine shop to weld me a new one (just like the old one, so the turbo wouldn't move) for the price of materials (I supply the materials and he turns them into a manifold for free).

So far it sounds like a no-brainer.

I don't intend to keep the car for too much longer, so a shiny new manifold just doesn't seem worth it. I also don't like having a cracked manifold either.

I guess the basic question is what would you do in this situation? My options as I see them are:

1. Continue to have the old manifold repaired every couple months as it develops new cracks - Free but a pain in the ***

2. Have a new manifold built out of stainless - $200ish

3. Have a new manifold built out of mild steel - $179 or less

At this point I am leaning toward option 3 and seeing if I can get the parts a little cheaper. Thoughts?
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Old 06-12-2009, 02:40 PM   #2
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Option 2.

What if you decide to keep it longer?

What if the new owner contacts you bitching about the cracked manifold?

It's $30 more than mild steel.
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Old 06-12-2009, 04:24 PM   #3
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get a better job so you can wipe your *** with $200 instead of welding weekly.
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Old 06-12-2009, 04:39 PM   #4
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get a better job so you can wipe your *** with $200 instead of welding weekly.
I'm working on it. Had an interview on Wednesday at a place that will pay roughly 3x what I make now. You may have heard though, the job market isn't great for those of us fresh out of college.
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Old 06-12-2009, 04:57 PM   #5
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It's a no brainer, do option 2, do it right. Selling a car with problems you know will happen = weak.
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Old 06-12-2009, 05:03 PM   #6
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How is making a quality manifold out of mild steel selling a car with problems? Aren't most of the cast manifolds around here something other than stainless? The $200 price was an estimate, I don't think either of the flanges from JGS are stainless, and those tend to be tough to find. Is a SS manifold with MS flanges a bad idea?
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Old 06-12-2009, 05:19 PM   #7
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Originally Posted by skidude108 View Post
How is making a quality manifold out of mild steel selling a car with problems?
I believe he was referring to option 1, "Continue to have the old manifold repaired every couple months as it develops new cracks" on the premise that it would continue to develop new cracks after you had sold the car.
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Old 06-14-2009, 05:07 AM   #8
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Quote:
Originally Posted by skidude108 View Post
How is making a quality manifold out of mild steel selling a car with problems? Aren't most of the cast manifolds around here something other than stainless? The $200 price was an estimate, I don't think either of the flanges from JGS are stainless, and those tend to be tough to find. Is a SS manifold with MS flanges a bad idea?
Ive done it on my downpipe but that was about 2 feet pre cat i switched over to 3" mild steel from 2 1/2" SS. Now there are major differences in heat cycles the latter being the manifold. Constant heating and cooling espicially with dissimilar metals (although the only difference is 12+% of chromium/nickel) can potentially create problems down the road. OTOH its not like your joining cast iron and stainless using FCAW. If it were me i would make it all the same metal.

A few quick questions about the previous manifold.

1. Thickness
2. Did the "good" welder back purge while welding?
3. What welding process did he use?
4. Did he get full penetration?
5. What filler rod?
6. Where does it crack?


1. If its thin **** it is more prone to crack than say schedule 40 pipe
2. Without a back purge you are burning the chromium out of the metal creating the *sugaring* which will in turn cause stress risers and crack.
3. Im just curious on this one
4. Without full pen the pipe will already have stress risers in the weldment and be more prone to failure.
5. Im assuming your using 304 base metal since thats the cheap **** everyone buys (it works great for this crap) Important to know what kind of filler rod he used. I use 308L which is low carbon rod which aids in preventing martensetic. Martensitic is a property of alloys that allows them to be hardened but the downside it takes away from ductility.
6. If the crack started at the weld then most likely the stress riser gave way. We all know about thermal expansion and you add 1 flaw... time makes fools of us all right?

Last edited by SKMetalworks; 06-14-2009 at 05:09 AM. Reason: wording
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Old 06-15-2009, 09:02 AM   #9
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sbkcocker, sorry, I don't know the answer to many of those questions. The thickness of the pipes was something pretty decent. I want to say it was sch. 40 but don't quote me. I don't know about back purging, he was using a mig with gas to weld, no idea on the penetration. I almost doubt it in most places because the weld only shows from the front. Don't know about the filler rod, and it cracks on the welds where the Ls meet the Ts. So far it hasn't cracked where either of the flanges meet. The first crack was on the top side and the second and third cracks have been on the underside.
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Old 06-15-2009, 01:42 PM   #10
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So I'm leaning toward a new manifold out of mild steel because I had forgotten how expensive/hard to find SS flanges are, and I don't really feel like having it made out of two materials. Doesn't matter, most manifolds are MS anyway.
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Old 06-15-2009, 02:14 PM   #11
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Just use stainless runners with MS flanges. I believe full-race makes all their manis like that.

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Old 06-15-2009, 05:53 PM   #12
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But then you run into the possibility of the dissimilar metals expanding and contracting differently causing unnecessary stresses... so far nobody has mentioned a single reason not to just make the entire mani out of MS...
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