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Old 12-05-2011, 02:28 AM   #1
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Default Downpipe Bracing - What Works and What Doesn't?

So I am working on a new custom setup for my '94 (pics below) and I am contemplating what I should do to brace the manifold/downpipe.

My previous setup (ETD long tube) cracked the manifold runners 1 and 4 where they met the flange, and also cracked where the downpipe met the turbine flange. It had a 6" flex joint in the downpipe and everything lasted about 15k miles of dd/autocross/some drag racing. I am thinking the added weight of the 3" exhaust contributed - I can hear it banging the rear brace when I corner really hard so its definitely moving around quite a bit back there (side note, any good ideas for reducing side to side movement of the exhaust without adding NVH??)

With this new setup I would like to make sure I don't do anything that could lead to premature failure. I saw how FM was bracing their downpipes to the tranny, but I thought I read that some people were having issues still? What about the BEGi brace method? I am using v-bands so I cant copy the BEGi method verbatim.

My new manifold is schedule 40 (.140") which is the beefiest I could find. And I have a flex joint at the end of the downpipe. However once I got it bolted up, I grabbed onto the exhaust and shook it back and forth to see what would give - surprisingly it looked like all of the flexing was taking place in the manifold/front portion of the downpipe and the flex joint wasn't doing much flexing at all. Is the flex joint too far back? I could move it ~4" further forward but thats about it before I risk clearance issues with the tranny and frame. I did notice that the old one, after thousands of miles of use, was MUCH more flexible than the new one so maybe it just needs to break in?


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Old 12-05-2011, 02:44 AM   #2
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Originally Posted by mx592 View Post
(side note, any good ideas for reducing side to side movement of the exhaust without adding NVH??)
I am using the polyurethane exhaust hangers from corksport, they really helped a lot with side to side exhaust movement.

As far as bracing goes, I haven't used any, but you'll want to get input here from hustler or savington about what bracing the absurdflow setups are using.

One thing i do recommend, is to put a flex section for the wastegate tube before it reroutes into the exhaust. That area can heat up in different patterns than the exhaust, and cause stress cracks to form. Also it gives a tiny bit of play which helps when you'te bolting everything together.
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Old 12-05-2011, 06:34 AM   #3
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That setup looks badass, did you build it?
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Old 12-05-2011, 09:39 AM   #4
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I am using the polyurethane exhaust hangers from corksport, they really helped a lot with side to side exhaust movement.

As far as bracing goes, I haven't used any, but you'll want to get input here from hustler or savington about what bracing the absurdflow setups are using.

One thing i do recommend, is to put a flex section for the wastegate tube before it reroutes into the exhaust. That area can heat up in different patterns than the exhaust, and cause stress cracks to form. Also it gives a tiny bit of play which helps when you'te bolting everything together.
Thanks. Do you daily drive your car? I have shyed away from PE hangers becuase I know they are going to increase NVH, and its already loud enough with the top up. I tried an expirement this summer, where I cut up a coathanger and fastened one end to the exhaust with a worm gear clamp and the other end to the rear brace with another wormgear clamp. It allowed the exhaust to move up and down as well as to the left (the wire would just bow) but not to the right, which is where it hits normally. It prevented the banging sound on hard cornering but I couldn't believe how much noiser it was! It made a buuzzing sound on decel.
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Old 12-05-2011, 09:40 AM   #5
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That setup looks badass, did you build it?
Yes sir. Build Thread: https://www.miataturbo.net/build-threads-57/winter-turbo-build-custom-equal-length-tial-v-band-goodness-61959/
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Old 12-05-2011, 10:19 AM   #6
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There are two schools of thought.
I consider this the thin-walled example:

And this is the schedule-40 example, ultra high-tech example I came up with to stop breaking exhaust hangers at the bumbiest track on Earth:


I'd still like to do a crane on mine, but I don't really have the money, it's a logistics nightmare to drop my car off somewhere, and I don't think us Tial V-band housing guys have enough room to mount to the CHRA bolts because it's already tight as hell.

Are you running Inconel, safetywired CHRA hardware? If not, you should be. Also, youre wastegate dump-tube is going to break.
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Old 12-05-2011, 10:26 AM   #7
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Ohh yah. If your wastegate has the water cooling ports, I highly suggest you use them. Or else it will not stay black at all.
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Old 12-05-2011, 10:33 AM   #8
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Ohh yah. If your wastegate has the water cooling ports, I highly suggest you use them. Or else it will not stay black at all.

After one day on the track my wastegate turned bronze, but even after 100-hours the diaphram is still good.

Lars, get some fire-sleeve over that hose and reroute it. You're in the danger zone, broski.
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Old 12-05-2011, 11:09 AM   #9
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Lars, get some fire-sleeve over that hose and reroute it. You're in the danger zone, broski.
The feed hose has been shortened a good bit and now feeds under the manifold. That is just a really old picture.
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Old 12-05-2011, 11:53 AM   #10
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Wrap it in fire-sleeve and use silicone tape on the ends, I melted an SS/rubber hose a long time ago on my car. BatInc is the way.
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Old 12-05-2011, 12:26 PM   #11
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Originally Posted by mx592 View Post
Thanks. Do you daily drive your car? I have shyed away from PE hangers becuase I know they are going to increase NVH, and its already loud enough with the top up. I tried an expirement this summer, where I cut up a coathanger and fastened one end to the exhaust with a worm gear clamp and the other end to the rear brace with another wormgear clamp. It allowed the exhaust to move up and down as well as to the left (the wire would just bow) but not to the right, which is where it hits normally. It prevented the banging sound on hard cornering but I couldn't believe how much noiser it was! It made a buuzzing sound on decel.
Yes I do daily my car, thats its only purpose right now. Once school is done i might swap back some stock rubber ones to see if i hear an increase of noise with the poly ones, but so far i can't contribute any increase of noise to them. The largest culprit of noise from changing hangers is probably sound coming up from the rain rail vents.
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Old 12-05-2011, 12:42 PM   #12
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The hangers don't do much other than help stop front to rear movement, my exhaust was still flung around violently.
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Old 12-05-2011, 01:23 PM   #13
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May seem ghetto as ****, but I used this hanger/brace to keep my DP from hitting the tranny and tunnel, and it transmits essentially no NVH to the car itself thanks to the rubber portion. I bolted one end to the PPF (iirc...have not been under there in a while), and attached the other end to the DP with a U-shaped exhaust clamp, double nutted as tight as I could get it. Been like that for months/thousands of miles and has not let go yet. There is another hanger similar to this with a longer rubber portion which replaces the metal strap, but this one kept everything fixed in place better.

Walker part number 35210, $10 at Advance Auto.
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Old 12-05-2011, 01:49 PM   #14
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Even more ghetto; I made an "L" bracket with a hole in it, put in a longer transmission bolt through so that I had threads sticking out the front and mounted the "L" bracket solidly on the transmission. Then with a standard exhaust "U" clamp, I pulled the DP hard against the transmission. Keeps everything forward tied together.
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Old 12-05-2011, 02:00 PM   #15
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Are you running Inconel, safetywired CHRA hardware? If not, you should be. Also, youre wastegate dump-tube is going to break.
I assume you are referring to the bolts which hold the turbine housing to the CHRA? Is this a known issue? If so, why doesn't Tial supply it with Inconel bolts? Is it due to the greater expansion coefficient of the SS housing?

About the dump tube - its not finished yet. It will have a flex joint as well as a slip joint where it merges back into the DP. It's got about another 18" of tubing that I have yet to fab. I would like to put the flex joint closer to the wastegate but I don't think there is room - seems like it wont do much if I mount it under the car near the slipjoint?
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Old 12-05-2011, 02:14 PM   #16
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It seems like the solutions above are adressing two different (but related) issues;

1 - The "crane" setup basically just helps to support the weight of the turbo, downpipe etc. but due to the heim jointed ends it cannot restrict any torsion or side loads generated by side-to-side exhaust movement.

2 - The exhaust brace solutions would help to restrict the side-to-side movement of the exhaust and therefore greatly reduce the torque applied to the manifold/downpipe. For me the key would be restricting exhaust movement without adding NVH - bracing the exhaust to the transmission or PPF is one way to do this since the whole powertrain itself is effectively isolated from the chassis. FM's brace is a good example of this: http://www.flyinmiata.com/index.php?...umber=06-97577
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Old 12-05-2011, 02:16 PM   #17
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Originally Posted by olderguy View Post
Even more ghetto; I made an "L" bracket with a hole in it, put in a longer transmission bolt through so that I had threads sticking out the front and mounted the "L" bracket solidly on the transmission. Then with a standard exhaust "U" clamp, I pulled the DP hard against the transmission. Keeps everything forward tied together.
I was considering something similar, my only concern with this solution is that it is not very forgiving to thermal expansion and contraction. So unless is has some give or slip, it might actually increase the stress on the manifold.
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Old 12-05-2011, 02:20 PM   #18
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Ohh yah. If your wastegate has the water cooling ports, I highly suggest you use them. Or else it will not stay black at all.
Thanks for the tip, and yes it does have water ports. i wasn't going to use them but after seeing hustler's I am reconsidering.

I don't track my car, only autocross and the occasional drag race so I don't know if i would have the same issue but its (realtively) easy to do so why not.
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Old 12-05-2011, 02:22 PM   #19
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Originally Posted by mx592 View Post
I assume you are referring to the bolts which hold the turbine housing to the CHRA? Is this a known issue? If so, why doesn't Tial supply it with Inconel bolts? Is it due to the greater expansion coefficient of the SS housing?

About the dump tube - its not finished yet. It will have a flex joint as well as a slip joint where it merges back into the DP. It's got about another 18" of tubing that I have yet to fab. I would like to put the flex joint closer to the wastegate but I don't think there is room - seems like it wont do much if I mount it under the car near the slipjoint?
Yes Hustler is referring to the bolts that hold the CHRA to the exhaust turbine. It is a known issue that hustler, savington, and I have had with our V-Band setups on the track. Tial now does supply Inconel bolts. You still need to find a machine shop that is able to drill them. Hustler knows a shop in Texas that can do it. Or you can send your bolts to TurboTim and he can do it.

It is good that you are routing the dump pipe back into the down pipe. Savington tried running his without plumbing it back in and I believe it cracked on the track. I will try to grab some shots of my wastegate tube tonight when I get home from work.
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Old 12-05-2011, 02:52 PM   #20
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Originally Posted by shuiend View Post
Yes Hustler is referring to the bolts that hold the CHRA to the exhaust turbine. It is a known issue that hustler, savington, and I have had with our V-Band setups on the track. Tial now does supply Inconel bolts. You still need to find a machine shop that is able to drill them. Hustler knows a shop in Texas that can do it. Or you can send your bolts to TurboTim and he can do it.

It is good that you are routing the dump pipe back into the down pipe. Savington tried running his without plumbing it back in and I believe it cracked on the track. I will try to grab some shots of my wastegate tube tonight when I get home from work.
Wow thanks for the info, I had no idea. I got my Tial housing less than 2 months ago - how would I know if the bolts are the newer inconel variety? Is Inconel magnetic?

I should be able to drill the bolts myself, I do have a mill available and some cobalt drill bits.
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