Simple DIY Manifold
 

Hello turbo cats, I just wanted to share my turbo manifold project with you all, this is my first time trying so all feedback is welcome!

I started out by attempting to make a proper turbo header, but after realizing this was very difficult, especially for a newbie like me, I decided to tackle the more traditional "log style" manifold. If you want more pictures/cad files/simulations just send me a message and I will do my best to help out.

The first step in making the manifold was to purchase the tubing bends and couplings, I went with 48.3mm( 2 ish inches) tubing with a 2.8mm sidewall. I chose to use relatively thick material as I do not want it to crack or be affected by the weight of the turbo, this is also the closest diameter I could find to match the exhaust ports. Since I can only attach 3 images I will be using IMGUR to show my progress.

Tubular bends and parts

I made a quick sketch up in CAD of how I wanted it to turn out and then double checking the dimensions with reality before I started to hack the bends, This is how I calculated how much of each bend to cut in order for them all to line up properly.

How I knew how much to cut from each piece.

Since the distance between them was 27mm, I took half of that distance from the T fitting and the other half from the 90 bend. I think it turned out just fine with the fitment,

The next thing I did after making all the bends the correct length and width I Hammered the "port connecting" part of the T bend flat to ensure that the weld fillet wouldn't interfere with the hole where the engine stud goes through the exhaust flange, this also made the T bend a bit wider which led to a better fitment, This was done with an Oxy-Acetylene torch and an anvil. unfortunately, I have no images of this except in the final product where it's visible.

When all the pieces Were cut to size with a hacksaw I used an angle grinder to remove the black paint from them and tacked them together.

Tacked together manifold

After the manifold was tacked together I Test fit it in the engine bay to decide where I wanted the turbo inlet flange to sit, I found a spot and Created a round -> flat adapter plate thing,

Turbo flange (pardon the mess)

When everything had been test-mounted in the engine bay I drilled a hole in the manifold for the turbo flange, and proceeded to weld the rest of the manifold entirely. (if you are going to make a manifold, remember to bolt your exhaust manifold to something rigid as it WILL deform under high heat, I used a thick piece of steel square tubing).

Here is the final product, If you have any tips of general feedback I would highly appreciate it.

PS, Dont mind the 3d printed orange wastegate bracket, it was just used as a template before making a steel one.

Thanks for reading

//Davinci

where did you get the flange?

Where did you get the pipe pieces?

All the flanges (exhaust flange, turbo inlet flange and turbo outlet flange) were made locally at a water cutting company, I sent them the cad files for my flanges and picked them up later that day.

I bought the piping bends at a Swedish auto parts performance store called jspec.se (Swedish), they are an industrial standard called A234 WPB steel.

2.8mm is Sch10, it will crack eventually, 100% chance of that.

You want 3.5mm, Sch40, which will also crack eventually, but it will take much longer.

I just checked and its 3mm, I´ll use it for now and be cautious and maybe upgrade in the future if it breaks, thanks for the reply!

Haha. This happens at least twice a week. Enjoy your failure.

Id like to see their posts regarding their issues, where I come from a 3mm turbo manifold is considered oversized, Standard is 2.4 at tuning shops.

Search and you'll find them. In the US we refer to the two common sizes as Schedule 10 (0.110") and Schedule 40 (0.140"). Most tuning shops use Schedule 10, but that doesn't hold up on these engines. Schedule 40 is required if you want any sort of long-term longevity. With a short, stubby manifold like yours, Sch10 will last longer than it would on a long-runner tubular, but eventually, it will succumb to the same failure.

At the end of the day, there are two kinds of tubular manifolds: those that have cracked, and those that will crack

Do some searching on this forum and you will see what these guys are talking about. Lots of other cars run around with manifold built out of thin tubing, but the Mazda B series destroys manifolds. Speculation is that its the result of some kind of harmonics (Im not sure if the cause has ever really been confirmed). There are numerous threads about broken manifolds, issues with hardware, etc.

That being said, for a street car this manifold may hold up for a while. You could put some extra bracing on it and see what happens. Worse case you can go back and buy a Kraken manifold and modify your downpipe to fit. But, if you want it to be right from the beginning, you should go ahead and get the right manifold.

Yes, I see your point about it being "thin" and you might be right, just seems so strange to me that that can happen a 3mm steel tube, can crack that easily. I tried using the search function for finding posts and threads with manifold issues but I must have done something wrong as the only posts I find are people asking what manifolds to buy. Appreciate your input.

Search by Google thusly: site:miataturbo.net search subject

Where search subject is what you are looking for. Can be a phrase in quotes.

See my build thread for my experiences. Been holding up for a while now, but only one track day at 175WHP

Usually the tube wont crack, the welds where it joins do.

Under full load there's a shitload of heat there, with the metal expanding and contracting all at slightly different points, which means bits eventually crack.

Steel does funny stuff when it gets all glowy.

Manifolds that work forever on Hondas and Nissans die a quick death on our rough running agrarian little engines. It's just the way things are. Every engine design has its particular quirks. Part of the reason we have a forum is to share experiences and insight so we don't all have to learn everything on our own.

Savington gains nothing if you get a thicker or thinner wall tube.

Im back ladies, Just came back to the forum and found this old post and thought I would give a quick update!
I have now driven my car at .9Bars (13psi) for more than 2 years (about 10k miles) and this manifold is still holding up with no signs of cracking or damage. I guess its true what they say about swedish steel :rolleyes:.

I know it wont last forever but its a cheap manifold to get out on the road and have some fun. I could build 10+ of these for the price of one cast manifold. It might not be for everyone but I would highly reccomend people giving it a shot if they have a welder, some free time and appreciate fabrication.

The one thing I would advice people to do is think through the type of flange they use, I have thought about changing turbo, but there arent so many to chose from when using this type of mitsubishi/subaru triangular turbo inlet flange.

Good to hear!

***also, you mean, you can purchase the material to make 10+ of those log manifolds for the price of an already made retail cast manifold. Everyone doesn't have the same value of their time.

Youre definately right, at the time I was a student, and considering how much time I have wasted playing computer games, I am now thankful for any time I spent in the workshop gaining experience. Im still a student in college and cosidering the circumstances with corona, free time is all I have and suspect a lot of other people do aswell.

I just hope this thread might encourage someone to give it a shot, try fabrication, its very rewarding.

Indeed. I went to wood. But... that slowed down a bit with the prices :vash: