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 Post subject: Mounting Exhaust Options
PostPosted: September 3, 2019, 6:46 pm 
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Joined: December 6, 2017, 2:20 pm
Posts: 123
Location: San Jose, California
Hi All,

My miata engine are on stock rubber mounts. I plan to hard mount part of the exhaust to the frame, then connect the exhaust manafold to the exhaust to the muffler via a 6 inch flex pipe. Do flex pipes offer enough flexibility?


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PostPosted: September 3, 2019, 10:11 pm 
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Joined: December 1, 2013, 10:48 pm
Posts: 63
Location: Atlanta GA
I never had or needed one in 8500miles. Mine was rigid mounted to the chassis


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PostPosted: September 3, 2019, 11:04 pm 
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Joined: July 17, 2008, 9:11 am
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Location: West Chicago,IL
IMO it is poor practice to hard mount the entire exhaust system. Too much engine vibration and torque twist that will transfer to the hard mounts and cause stress over time. Perhaps the flex connector will work for you. I have seen these fail over time in production cars.

What is the objection to flex mounting the exhaust system?

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“Any suspension will work if you don’t let it.” - Colin Chapman

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PostPosted: September 4, 2019, 6:27 pm 
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Joined: October 10, 2010, 10:26 am
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Location: Santa Maria, CA
I've just integrated a 4" (@2.5" dia) flex pipe section into my 1800 build.. I felt I needed it as my exhaust tips are solid mounted where they poke through the rear valance..

The flex section I used was had from Summit Racing, and to answer your question, it has plenty of flex.. I can't as of yet speak to longevity as it's only been in service for a short time, but I too have heard they have a relatively short life.. It seems well made and should be ok, but time will tell..

--ccrunner


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PostPosted: September 6, 2019, 3:17 pm 
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Joined: July 4, 2006, 5:40 pm
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Location: Novato, CA
Having had several rubber exhaust hangers fail (the book design is rubbish), I was tempted to hard mount the exhaust, but figured out something better. The flex pipe is a good solution except for the way it looks.


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PostPosted: September 7, 2019, 7:38 am 
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Joined: September 22, 2005, 8:12 am
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Location: 4AGE in S.E. Michigan
You could look at using springs as exhaust hangers. The spring allows movement, and very little vibration transmitted to the body. The only trick is the bolt thru the center of the bracket needs a small section of rubber tubing between the bolt and bracket. So the bolt does not have metal to metal contact. The NICE garage rug is optional :D
Davew


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PostPosted: September 7, 2019, 9:14 am 
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Joined: October 24, 2008, 2:13 pm
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Location: Carlsbad, California, USA
@nick47
@davew

I kind of agree with both of you.

I think the flex section is a decent solution if you can hide it inside the engine compartment. I've already planned out my exhaust hanger locations and was searching for photo of what I have in mind to use as a system. It's an old school solution using springs, but I could not find a photo to share.

However, Dave's solution is nice too. Surprisingly, I found several examples of it while searching for the one I have in mind. The good news is you can buy ready made versions from places like O'Reilly's Auto parts. Here's just one example:
Attachment:
File comment: Example from O'Reilly's
Sprung Exhaust Bolts.jpg
Sprung Exhaust Bolts.jpg [ 12.04 KiB | Viewed 315 times ]


Here's a URL to a webpage of several examples.

Cheers,

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PostPosted: September 7, 2019, 8:59 pm 
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Joined: July 4, 2006, 5:40 pm
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What put the biggest strain on the book-sty;e bobbin hanger was the heat expansion of the exhaust pipe, about 1/4" longer when hot. The spring bolt solution allows the pipe to move with the engine, but puts some stress on the whole exhaust when it heats up. In the end I went with a standard two-peg hanger.


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PostPosted: September 7, 2019, 10:17 pm 
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Joined: July 17, 2008, 9:11 am
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Location: West Chicago,IL
Image

This was my hanger 2.0. Originally I had the pins 90 degrees from this, one facing outward from the chassis and one welded to the muffler. There was enough movement from the engine that it would unhook itself. In this orientation, they cannot disconnect. It does require unbolting the mount from the chassis to remove the rubber hanger. Not really a problem IMO.

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