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Old 02-28-2009, 03:41 PM   #1
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Default Custom Exhaust Manifold is cracked / has hole... what could have caused this?

Im trying to figure out what could have caused this and have a few ideas so far. I am yet to take the exhaust manifold off the car to see exactly what has happened. About a week ago under any throttle above 1500 rpm's theres a loud exhaust leak that ticks(usually indicates a pre turbo leak). I checked the bolts holding the manifold in place hoping a few nuts got loose and while looking around for the leak, I gave the car a little throttle and was able to see some of the heat wrap around the manifold shooting out little dust particles indicating the hole is on the front section of the exhaust manifold. The red box indicates roughly where the hole is and its on the bottom side of the manifold (the side closest to the ground). The picture of the engine is not current...and i know theres a few issues with that setup. Any suggestions are appreciated.

Possible problems
-To much weight on the manifold due to turbo set up
FIX = Build custom brackets for manifold and turbo

-Material it was crafted from is to weak
FIX = Use better material, heat coat it

-Engine shifting under load with extra weight cracked it
FIX = HD motor mounts or chains to help engine from flexing as much

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Old 02-28-2009, 04:17 PM   #2
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What manifold is it? I'd like to see a picture of the manifold, something closer up atleast to see which one it is.
What is the manifold made of?

It's hard to recommend much without knowing which manifold it is. It might have cracked due to lack of relief cuts but that is manifold dependent.
Standard recommendation would be to fix the manifold and brace it to take the weight off the runners. Maybe brace the downpipe as well so the turbo and manifold aren't supporting the weight of the downpipe and exhaust.
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Old 02-28-2009, 04:25 PM   #3
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I will report back with pics as soon as the manifold is off the car. It was an ebay manifold (i think made from stainless steel) that i cut the turbo flange off of and then welded on a new flange for my turbo.
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Old 02-28-2009, 04:32 PM   #4
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That's the problem.
Read here. The ebay manifolds are built with cheap tubing, they all crack eventually, especially without bracing. Buy a real manifold.

https://www.miataturbo.net/forum/t19358/
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Old 02-28-2009, 04:39 PM   #5
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Yeah, post up a detail pic so we can get an idea of the "weakness" that might have led to it.
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Old 02-28-2009, 04:45 PM   #6
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Buying one is not an option as its a custom turbo setup. Other than starting with a new manifold and welding onto that one is there anything that can be done to strengthen my current POS ebay manifold?
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Old 02-28-2009, 05:42 PM   #7
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why dont you actually get some pics so we dont have to work with only speculation.
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Old 02-28-2009, 05:46 PM   #8
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i like your heater core outlet plumbing... and your blocked breather line.
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Old 02-28-2009, 05:53 PM   #9
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Halp u guyz i want 2 kno y my ebay manifold broke :[
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Old 02-28-2009, 06:06 PM   #10
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Quote:
Originally Posted by Braineack View Post
i like your heater core outlet plumbing... and your blocked breather line.
LOL @ heater routing. As far as the crank lines go, most of the big daddy turbo set ups I see have the breather end plugged with a big PCV on the other end going to a catch can and then the intake manifold. I've also seen them going to the exhaust instead of the intake manifold, supposedly if you do it correctly, the exhaust flow will suck fumes through and burn them without getting the mess into the IM.
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Old 02-28-2009, 07:16 PM   #11
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Heater core was removed, valve cover breather has since been routed into the intake... thats why i said please excuse the outdated pics but anyways here are the pics of the crack in the manifold.
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Old 02-28-2009, 07:33 PM   #12
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An ebay manifold cracked. Damn, that's never happened...
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Old 02-28-2009, 08:09 PM   #13
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was it always wrapped? it's the nature of that manifold to crack, really.
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Old 02-28-2009, 08:29 PM   #14
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Weld it up and wait for it to crack again, brace it this time, might last an extra week.
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Old 02-28-2009, 09:13 PM   #15
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I now realize its made of cheap metal... I am just looking for a way to use it for a bit longer until I fabricate another design. It was the first exhaust manifold ive ever made. I know that I could have bought a turbo that would have worked with begi's or another name brands manifolds but i wanted to use a wrx turbo.

To those that fabricated their exhaust manifolds, what did you use as a starting point?
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Old 02-28-2009, 09:16 PM   #16
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Search. Search for words like "manifold" "tubular" "weld-ell" "pipe" and things like that. Schedule 10 and Schedule 40 pipe works very well to make runners for a manifold. Last forever and never cracks if you weld it up half way decent.
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Old 02-28-2009, 09:30 PM   #17
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Turbo Header kits WARNING! FABRICATION REQUIRED!!!!!!!!!!!!!!!!!!!!!!

They sell a miata specific log manifold kit that takes all the work out of sourcing parts.
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Old 02-28-2009, 10:37 PM   #18
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My plan for the WRX turbo:
You can take a cast mani for a T25 made by FM or Begi or HKS, etc., and buy two things from Weirtech. A T25 flange and a Subie flange. Orient them so you can get to the bolt holes on each and weld the two flanges together. Bolt the T25 part down to the mani and the Subie part to the turbo.

Or just weld the Subie part to the cast mani if you don't think you will ever go to a T25 in the future.

I'm going to try to do it the first way to preserve the integrity of the manifold.

If you are building your own mani, Weirtech has really nice flanges for the part that bolts to the head also...
weiRtech
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Old 03-01-2009, 01:15 AM   #19
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or, you can bother ETD racing to make another one of this:

Custom Exhaust Manifold is cracked / has hole... what could have caused this?-dsc00460.jpg

but seriously, you could get one of these:

eBay Motors: 89-93 MAZDA MIATA 1.6L B6 CAST T3/T4 TURBO MANIFOLD (item 250380055633 end time Mar-02-09 17:38:31 PST)

and make an adapter plate that has countersunk bolt holes for the T25 flange and through-holes for the IHI/Subaru flange.
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Old 03-01-2009, 07:56 PM   #20
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Pipefather,
That shore is purty! I'm sure it was a few bucks more than I was willing to spend, though.
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