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I want to make my own turbo exhaust manifold - Gen 1 RX7

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I want to make my own turbo exhaust manifold - Gen 1 RX7

#1 Post by arran » Wed Sep 30, 2015 9:58 pm

Hi all,

Might anyone suggest where I could get the bits and pieces needed to make up my own exhaust manifold? The manifold I have on the cur currently has cracked twice so I want to replace it.

I think it best to use stainless, 304 schedule 10 seems to be used commonly.
I want a 13b flange, s5 turbo foot, and it is to go in a gen 1 rx7, turbo is internal gate.

Thanks in advance,
Arran


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#2 Post by WANKfactor » Thu Oct 01, 2015 5:43 am

Where abouts did it crack? I believe i have the same manifold (no names) albeit shortened and modified for twin gates and the turbo is hung on a pendulum brace.

will be watching this space as last time i tried to find ss steam pipe and butt welds it was a headache to say the least, and pretty sure i will be doing the same once mine has cracked a couple of times too.


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#3 Post by arran » Sat Oct 03, 2015 5:45 pm

Hi all,

Looks like i'll be putting a hold on the new manifold. I've just put the car back on the ground after jacking it up to take a good look at what was going on, I found that one of the bolts from CHRA into the turbine housing has fallen out. It was one of the bottom ones so was had to spot and quite difficult to get back in. All good.

I did make a couple of phone calls and had a comment that steam pipe rather than stainless was better for this application, I don't actually know why.....

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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#4 Post by WANKfactor » Wed Nov 04, 2015 7:41 am

There is a seller doing 304l steam pipe and butt weld on Ebay, works out pretty cheap for a twin rotor manifold, but am wondering if 304 is good enough? I have heard that mild steel steam pipe is better too, and that 321 isbetter than 304, but i dont know where to get hold of it.

Little help? What should i use? 304, mild, or try and find some 321?


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#5 Post by arran » Tue Jan 26, 2016 10:41 pm

Going to proceed with this manifold again, I've contacted ecsengines for the steampipe, and SDR Motorsport for the flanges.

I spoke to Blackwoods who have a great online catalog but weirdly they could not sell me straight pipe in anything less than 6m. That was for NB40 pipe. The NB50 pipe only came in 12m lengths. ecsengines seem to offer 1m lengths in their ebay shop, so see how that progresses.

I'll need to tap in 1/8npt x 2 for the EGT sensors, and I'll look at getting this one ceramic coated if it works as well as a heat shield.
I want to try to fit in NB50 pipe as it has almost double to CSA compared to NB40.


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#6 Post by arran » Fri Jan 29, 2016 1:15 am

WANKfactor wrote:There is a seller doing 304l steam pipe and butt weld on Ebay, works out pretty cheap for a twin rotor manifold, but am wondering if 304 is good enough? I have heard that mild steel steam pipe is better too, and that 321 isbetter than 304, but i dont know where to get hold of it.

Little help? What should i use? 304, mild, or try and find some 321?
I bounced the question on materials of a guy I know through the seven of clubs car club who is a mechanical engineer. His opinion was that the mild steel steam pipe would be better than Stainless steam pipe because it will crack under the heat load of a rotary exaust.

Another factor is the flange material. If you are going to be using mild steel flanges, you would not want to be using stainless runners. I'd guess that there is a difference in rates of expansion so you are going to introduce stress.

I'm going to get the Sch 40 NB 40 and 50 bends and straight from ECSengines. I received a quote today and the prices are OK
I'm getting the flanges from SDR, they have given me a quote also


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#7 Post by omp » Fri Jan 29, 2016 7:33 am

I see you are in Brisbane, if you are north side, hit up Daniel at Metallon (0401 071 655).

He has dealt with rotaries and manifolds in the past.

Recently had a rotor in his hilux before going to 1UZ V8 turbo, all fab work done there.



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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#8 Post by Ale » Fri Jan 29, 2016 6:19 pm

Hey mate, good to see your still around and DIYing it!!

Stainless looks nice and Ive seen it work very well, but IMO, for the average DIY, mild steel is a no brainer and much easier ( not to mention cheaper) to get right.

Ive probably made 20-30 in mild steel pipe, never had one crack, ever.
When I think back to the quality of the fabrication on the first ones I made as an apprentice , I cringe, they still survive 15 years latter.
Hot tips:
Fully vee out your joins, and use a tig welder to ensure a proper burn in, dont linish welds if you arent 100% confident, then wrap the thing.

Keep flanges thick, and have them machined after fab, tap holes in turbo base plate and use quality studs where possible with mechanical lock nuts.
Pain in the arse to tighten, but rather this than constantly having to tighten them as they rattle loose

Over the years, Ive got better and fine tuned the design. These days Id aim for an equal length, fully split design (regardless of turbo housing design) with the shortest runner length as possible.
Id think very carefully about waste gate integration, especially if running 25+psi boost.

I also try and match flange ends to pipe diameter.
Purely for example; if putting a T3 base plate on a 13b exhaust port, Id add concentric reducers in the runners for a nice transition from 50nb to 40nb. If using small 12a exhaust ports, Id run 40nb all the way up to a T3.

Ive done lots of street cars with the above, no issue's. On a race car, I except you can waiver from the above, but I wont pass opinion cos Ive done very little fab on race cars.

10 years latter this one still looks the same:

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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#9 Post by arran » Fri Jan 29, 2016 9:46 pm

Hey Ale,

Thanks for dropping by! That manifold looks spectacular, nice work. I'm fairly sure that mine won't be looking anywhere near as good as that :)
I have an AC TIG welder in the garage, 200A.

My idea is to try to keep the turbo located in the same position it is now so I don't need to change other stuff like intake duct, pipe to intercooler and especially the dump which is a split main exhaust/wastegate setup. This means templating off the SDR Manifold. I am using a high flowed Hitachi HT-18-2S Knightsport internally gated.

The way SDR has merged from runner to flange at the turbo is to oval the ends of each of the 45 degree bends somehow, it isn't a great transition but I don't think it is critical for making power, but would probably be seeing a lot of heat where a step is (which isn't where it cracked). For a Gen 1 RX7 though, the SDR does put the turbo right where it needs to go so I don't see any need to change that.

I hadn't considered using reducers to drop from NB50 at the engine to NB40 at the flange, that's a great idea. I've attached a pic of the SDR manifold, and there might be enough straight there to fit in a reducer.

Tapping the turbo flange holes is also a great idea. I'm buying laser cut flange from SDR, paid for it today, if it is the same as the flange on the manifold I have it is going to need a big bolt so I'm not sure I can do that unless I fill the holes and redrill. What about welding the nuts to the back of the flange?

The manifold wants to crack right where the two runners are welded together. I see with your manifold you have left both runners separate right up to the flange. I think that this gives more runner length over which heat distortion stress is spread so each given length of runner has to flex less. I'm sure that is no accident :)

I have heard about a lot of problems wrapping mild steel because of corrosion. Do you see that? That is why I was leaning towards HPC.

Arran
SDR_Motorsport_E_4b433547ce097.jpg


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#10 Post by WANKfactor » Fri Jan 29, 2016 10:21 pm

All the big-nob players building and selling manifolds in yankee-land seem to use the 40mm pipe, and bevel the flange. The SDR one i got wasnt finished at all, just raw welds. I portmatched my flange to the exhaust ports and ground the "step up" into a bull-nose - sort of like a mini velocity stack. Dont know if thats good or bad but doesnt seem to hurt performance.
As to HPC, i was turned off using it because kept getting told it will flake off mild steel when the carbon sweats out of the steel, and its a bastard to grind off should the need arise to repair cracks. Not to mention its not cheap.
Used flame proof paint, seems to hold up pretty good, cant see why you couldnt wrap over the flame proof. Aesthetically, the manifold isnt seen (at least on my set up) so looks dont really enter the equation. As for heat management I'm just using ACL sheet.

Looking forward to seeing how this comes along! Also a bit worried about the cracking issue as mine is the same thing (SDR) except shortened so will be even more susceptible.


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#11 Post by arran » Sat Jan 30, 2016 9:33 am

Thanks,

A friend of mine has the same manifold bought about the same time and hasn't had problems with cracks


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#12 Post by arran » Sun Mar 13, 2016 7:15 pm

I've had a bit of trouble getting hold of a manifold from which I can template my home made manifold so I don't need to keep pulling the car apart.

I called SDR Motorsport to see if they had any suggestions and for a very small cost Steve is going to use his shop template to orient the flanges and send them to me in Brisbane.

They should arrive in the next couple of days


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#13 Post by arran » Wed Mar 16, 2016 11:58 pm

Jigged up flanges arrived today. Any recommendations on welder setup? I'm using a 200A AC/DC TIG

TIG DC
What size electrode and filler rods?
Current setting?
Gas flow - usually set at 7L/min
Attachments
IMG_20160316_182118 (Small).jpg


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#14 Post by Ale » Thu Mar 17, 2016 10:59 am

LW1 filler wire, 1.6mm dia, amps around 120-150 maybe? Depending on your pipe prep and technique. Id be running a few more braces before you start.
Tack the runners up, but before attaching them permanently to the flanges fully weld the parts you can’t get to as nice once in position between the flanges if it makes sense.


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Re: I want to make my own turbo exhaust manifold - Gen 1 RX7

#15 Post by arran » Sat Dec 24, 2016 11:41 am

To close this thread out, a new manifold has been made, but not by me. I had repeated problems with my welder blowing up and I waited and waited but the crack progressed to a point that I needed to do something about it so bit the bullet and took it to the fabricator. I'm happy with the result even though it ended up costing quite a bit.

The crack can be seen in this picture near where the two runners come together. Second time it cracked there.
SDR Cracked.jpg
This new manifold has been purge welded and roughly honed internally. Chunkier 1/8 NPT bosses have been welded in for the EGT probes.
The main feature though is the path that the runners take. Because of the steering rack conversion I wanted to get a bit more clearance to the pinion and raising up the rear runner slightly achieved that, and allowed heaps of room for clearance to the heat shield. With the old manifold there was about 12mm clearance, which was enough, but with the new manifold I have about 30mm clearance even after the new shield is installed
New Manifold 1.jpg
New Manifold 2.jpg
Last edited by arran on Sat Dec 24, 2016 11:59 am, edited 2 times in total.


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