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PostPosted: December 29, 2016, 11:44 pm 
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Joined: October 12, 2013, 8:55 pm
Posts: 200
Location: Tucson, AZ
Running into an issue and I'm needing some help/guidance.
First off - here's my build log: http://www.locostusa.com/forums/viewtopic.php?f=35&t=15572&start=300
On that page you'll find the question but to reiterate:

Because of space constraints and my own lack of fabrication skills, I'm thinking of using a turbo exhaust manifold - I can't mount my pedal box with the master cylinders because they conflict with the exhaust manifold ('95 1.8L Miata Donor).
I've read some general forums and from what I can tell, I can use a much smaller (turbo version) exhaust manifold from ebay or flyin' miata - BUT according to the forums it does come at a performance loss. I'm not too concerned with loss of performance as this will not be a racer but rather a sunday driver...maybe a daily driver to work. But I don't want to break the engine or putt-a-long as slow as a granny either.

Any snippets of wisdom would be appreciated.
Thanks in advance for the help!

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PostPosted: December 30, 2016, 12:23 am 
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Joined: April 17, 2009, 1:28 am
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Location: San Tan Valley, Arizona
Dwight,
I can not answer your question about the turbo manifold, but, if the 95 Protege and Miata have similar cyl. head configs, then you might be able to use the Protege manifold. It has the flange pointing down, between #3 & #4 cyl.
If the gaskets are a match (or close), It might be another route to follow.

Walt


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PostPosted: December 30, 2016, 1:04 am 
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waltj wrote:
Dwight,
I can not answer your question about the turbo manifold, but, if the 95 Protege and Miata have similar cyl. head configs, then you might be able to use the Protege manifold. It has the flange pointing down, between #3 & #4 cyl.
If the gaskets are a match (or close), It might be another route to follow.

Walt


Thanks for answering!
I had thought about seeing if another from a different vehicle might fit, but figured that process would take as long as fabricating one. I reviewed images of the 95 protege that you mention and found that the bolts would most likely not match up - also compared online images of the two gaskets side by side and they seem very different.
Thanks for the suggestion though!

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PostPosted: December 30, 2016, 2:26 am 
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Edit: I only just saw that you are not actually using a turbocharger, so everything I wrote is irrelevant :x

Hey Dwight, a log-type manifold on a turbo engine is actually very effective. It will not offer the scavenging effects of a tubular manifold with a low-angle collector, however in most cases a log manifold will give better spool and will most definitely reduce chance of cracking in the manifold itself. Avoid the temptation to buy a cheap Chinese manifold that looks all polished in stainless steel; they will crack, and their figment is dreadful. I have been building turbo manifolds for many years for clients, and for a 4cyl under 300hp there is no tangible benefit, except for when pushing the envelope; as a tubular manifold will often reduce EGT's allowing you to run more timing. But this doesn't sound like your case, and as such KISS is a great way to go.

I use 45` and 90` cast bends together with "T" pieces that can be easily purchased, often refered to as steam pipe. Very important to have the steel ground to a chamfer to allow the weld to penetrate. A stick, mig or TIG is suitable. Bolt the exhaust flange to a thick piece of steel ( or an old head that you don't use) to avoid warping. It will still need to be machined afterward.


Last edited by Ewcarb on December 30, 2016, 3:44 am, edited 1 time in total.

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PostPosted: December 30, 2016, 2:44 am 
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Edit: I only just saw that you are not actually using a turbocharger, so everything I wrote is irrelevant :x

most people go way overboard on the internal cross section of turbo manifolds.

For torque, quick response and good power keep it small!

On a 4cyl up to 500hp I use 1.25" ID tubing, over 500-600hp I go to 1.5" ID.

Just a bit of extra info that may be superfluous:
I previously owned a turbo fabrication business, and built manifolds for international clients. We did some data logging on two very highly modified engines in the 800-1000hp range; 2JZ (Supra) and RB26 (GTR) and up to 800hp a 1" ID manifold (admittedly full tube runner style) was the better choice; as it gave a better power curve, response and did not limit the power at all.


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PostPosted: December 30, 2016, 12:16 pm 
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Joined: April 1, 2010, 10:26 am
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Don't discredit a log manifold because it does not look as sexy. Flyin Miata make a great manifold, it's been refined over the years, it may lack the very top end power but you get better spool at lower rpm. They are also very durable and should outlast the car , Don't over turbo the engine, you may get more power but they become more difficult to control ECU wise and tougher to drive physically. Anything up to 1 bar is smooth, powerful and easy to drive. With such a light are and big turbo power hits become difficult to control.

Graham


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PostPosted: December 30, 2016, 12:46 pm 
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Joined: October 12, 2013, 8:55 pm
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Location: Tucson, AZ
So, thinking about this for a few days....in the shower...I had an epiphany *EUREKA*.
If I cut the oem manifold about where the yellow line is in the picture I could weld a 90 degree bend on to it that could go straight to the side wall...then I could weld the original flange to the extension.
Gotta go take a look but figured I'd write it down before I forget the plan.

Thing is, I wouldn't be able to fabricate a whole new manifold....but I can modify the existing one....hopefully this will work!


Attachments:
File comment: yellow line is a rough guestimation of where I'd cut and splice
IMG_7209.jpg
IMG_7209.jpg [ 1000.33 KiB | Viewed 569 times ]

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PostPosted: December 30, 2016, 11:12 pm 
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Location: central Arkansas
Perfectamundo!

A 45 degree elbow might work as well as a 90. Order the elbow first, then cut where the diameter matches.

If the manifold is stainless steel, it can be a right ***** to cut with a saw. A cutoff wheel will work better. Use the narrowest one you can find to minimize any steps to the elbow.

If you buy a stainless elbow and have someone TIG it with a stainless filler rod, you can run the manifold bare, just like Mazda did, and not have to worry about rust, repainting, etc.


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PostPosted: December 31, 2016, 6:01 pm 
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Yup...i got a mig welder and it'll all be steel...so i think im all set...no one local has bends...all the exhaust shops are sh*t heads about it and the local pepboys only have a limited selection....thank god for ebay!

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PostPosted: January 1, 2017, 5:44 am 
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Joined: November 21, 2016, 4:33 am
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I am currently doing a how-to-make-an-exhaust-manifold-from scratch-with-basic-ish-tools video and will throw it up on YouTube; hopefully someone will find it helpful. Did three runners today and just one to go....filming and editing the video is much harder.


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image.jpeg [ 1.82 MiB | Viewed 499 times ]
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PostPosted: January 2, 2017, 5:55 pm 
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Ewcarb wrote:
I am currently doing a how-to-make-an-exhaust-manifold-from scratch-with-basic-ish-tools video and will throw it up on YouTube; hopefully someone will find it helpful. Did three runners today and just one to go....filming and editing the video is much harder.


Wow, that's impressive work...But I think I'm going to stick with modifying the stock one first, if that doesn't work I'll definitely have a look at your videos!
Thanks for posting!

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