Rear exit headers thermal expansion


bonehead

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Came to my attention a few months ago that the driver's side of my Borla rear exit headers (M9430-GTX) were contacting the lower rear mesh screen after a drive. Initially thought one of the spring brackets came loose but everything is connected. Haven't had time to get it back into the shop until a few weeks ago to have the CDC bumper delete kit installed. During that interval period, the repeated contact and heat actually scored an imprint of the mesh screen on the ceramic coating of the pipes.

Well, we had to shorten the tips for the bumper anyway, hoping this would also take care of the contact issue. As an extra layer of precaution, Evan Guyett put a layer of header wrap on the potential offending section. Drove the car home and immediately checked the pipe. Still making contact, albeit now with the wrap instead of directly with the section of pipe.



The exhaust fab shop shortened the tips as close to the transaxle as possible, so I don't think there's any other way to cut the length down any further.

Anyone else with the rear exits (Ralphie?) have this issue? Do I even need to worry about it as long as it doesn't damage the exhaust or the mesh screen?
 

BlackICE

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Nov 2, 2005
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SF Bay Area in California
I would try to adjust the exhaust so that when heated it is centered in the opening. There is probably some movement also from the engine when it moves in its rubber mounts.
 

PL510*Jeff

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The rear facia expands/contracts with both heat and speed.

Sign of playing hard.
 

RALPHIE

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Mar 1, 2007
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No known problem to date, Ed. But, I've never considered a bumper delete kit. My tips are centered through the bumper. They do seem to discolor the black bumper insert a little.
 

FENZO

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It was a challenge getting all the rear surfaces aligned properly when I did a bumper delete. Point being I think you could loosen a bunch of fasteners back there and persuade the mesh away from the exhaust a bit.
 

bonehead

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Not sure I conveyed my issue correctly.

First, I had the issue with the OEM bumper and rear fascia. The bumper delete kit has nothing to do with the problem.

Second, the issue isn't one of centering the exhaust in the bezel (i.e. Positioning up/down or side to side) but with lengthening of the header system with heat, i.e. fore/aft movement.

So by shortening the tips, our hope was that would solve the contact issues. Unfortunately, it looks like the system expands more than we have the ability to reduce it's overall length.

Does this make anymore sense?
 

Empty Pockets

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^ Yes.

Shadowman came up with the solution to this (assuming you're referring to the expansion of 4-tube headers). There's a whole thread on it somewhere around here.

'Will try to find it.



Edit: I think this is it:

http://www.fordgtforum.com/forums/showthread.php/6737-Shadowman-IMPORTANT-Stainless-Works-News?highlight=

...however, upon glancing thru it again, I'm not so sure it addresses your specific issue.
 
Last edited:

FENZO

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I didn't mean to imply that the bumper delete had anything to do with it, just that is the reason I was back there adjusting stuff. The rear facia is flexible and the clip nuts on the mesh itself have play. If you were to drop the rear belly pan, loosen all the fasteners in/around that location I'm betting you could pull the mesh out and re-tighten everything away from the exhaust.
 

Sinovac

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Ed,

Are the collectors seated all the way into the primaries and are the springs tight?
 

bonehead

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EP, thanks for the link, but no, I don't think that addresses my issue.

FENZO, I was referring to Ralphie's comment about the bumper delete. But thanks for your input. I think the amount that the screen would need to be pushed out would be aesthetically displeasing.

Paul, Evan did all the work, so I would assume all the connections are tight and seated. I'll see if I can get him to chime in here.
 

nota4re

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You had the rear exit headers ceramic coated. As such, you need to take great care to insure you are getting the full ~1.25" of overlap at the slip joints. If you are not getting all of this overlap, the system may be longer overall - thus causing the contact.
 

bonehead

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You had the rear exit headers ceramic coated. As such, you need to take great care to insure you are getting the full ~1.25" of overlap at the slip joints. If you are not getting all of this overlap, the system may be longer overall - thus causing the contact.
Thanks Kendall. But I distinctly remember Evan telling me he taped off the slip joints before sending them off for coating for just that reason. I asked him to chime in here when he has a moment.
 

Sinovac

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Loosen the exhaust brackets at the transaxle, wrap a wooden block in a rag, put the block squarely over the entire circumference of each exhaust tip, and give the block a couple of light hits. If you alter the clearance at the screens to any extent, the collectors are not fully seated. Don't hit the block hard, you are just trying determine if you can get some additional movement.

If this makes you queasy, find someone with rear exit headers (who doesn't have your problem) and take reference measurements from the header flange to the slip joints. Compare them to the measurements on your car. Longer on your car = improper seating.

Improper seating at the slip joint is the only logical explanation for the problem you are having. Absent some manufacturing defect, this is the only variable in the length of the header assembly. I can't imagine the rear fascia/screen would be so misaligned as to cause the problem.
 

nota4re

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Thanks Kendall. But I distinctly remember Evan telling me he taped off the slip joints before sending them off for coating for just that reason. I asked him to chime in here when he has a moment.
No doubt, but it is just not that easy. When we've installed slip joint headers, we will typically spend an hour or more with a dremel tool to get the full overlap that is designed into the system. As you are having "length" issues, I'd be pretty certain that this is the problem. Unfortunately the proper remedy is going to be a little labor intensive.
 

Xcentric

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Ed, As others have said, the slip joint between the primary and secondary would be the first thing to check. I'm not certain, but I think the joint is the same on the long tube and the rear exit headers. Mine were Jet-Hot coated and the join tubes were not taped off. Even so, besides having two secondary tubes a bit out of round (cured with a few rubber mallet whacks), the primary and secondary slid together and clearly felt like they bottomed out. We marked the tubes to make sure they went in to full depth.

You can see in the pics, there is no stretch to the springs. They are taut, but not stretched. IDK how close production tolerances are, but I would think if the tubes were 3/8" - 1/2" from being seated, you would see some stretch in the spring coils. OTOH, it seems to me that it would be obvious to anyone if the tubes weren't seating properly.

If you'd like, I could try to take some measurements...say between the spring attachment loops, but again, production tolerances may not be that precise.

Headers.jpg

IMAG1159-2.jpg
 

bonehead

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This is where is really like to get Evan's input as he was the one that installed the headers.

Separate but related question. If the slip fit is loose/not fully seated, would this cause an exhaust leak that would effect performance? Had a less than stellar outing yesterday at Airstrip Attack. Cars I should have easily taken by several cars were either losses or close calls. Very disappointed.
 

nota4re

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Separate but related question. If the slip fit is loose/not fully seated, would this cause an exhaust leak that would effect performance? Had a less than stellar outing yesterday at Airstrip Attack. Cars I should have easily taken by several cars were either losses or close calls. Very disappointed.
I think that the slip joints will leak a little bit on all car - but on NA or SC'd cars this minimal kind of leak would have no adverse effect on performance. This is a different story on the TT cars and likely one of the biggest performance gains we achieved between V1 and V2 of Heffner's TT kit was in eliminating theses joints. But, unless you are turbocharged, I wouldn't look toward these slip joints as being problematic at all.
 
Aug 25, 2006
4,436
All exhaust grow in length when hot however the long tube header design that goes straight back on both sides makes it more pronounced.

For example, I did thermal expansion measurements on the Stainless Works system and when extremely hot they grow in length nearly 3/4".

Having shared this, the Stainless Works have thermal expansion that I designed into the rear exit portion allowing for this and are routed with no thermal expansion issues however the Ford Racing aka Borla design is such that when it grows in length it is common for the final curve before the tail pipes to touch the rear screen.

I made it a practice to wrap this portion of the exhaust so as to prevent any secondary damage.

Takes care

Shadowman
 

bonehead

GT Owner
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Aug 18, 2012
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Houston, TX
All exhaust grow in length when hot however the long tube header design that goes straight back on both sides makes it more pronounced.

For example, I did thermal expansion measurements on the Stainless Works system and when extremely hot they grow in length nearly 3/4".

Having shared this, the Stainless Works have thermal expansion that I designed into the rear exit portion allowing for this and are routed with no thermal expansion issues however the Ford Racing aka Borla design is such that when it grows in length it is common for the final curve before the tail pipes to touch the rear screen.

I made it a practice to wrap this portion of the exhaust so as to prevent any secondary damage.

Takes care

Shadowman
Bill, thanks for your input. That bend right before the tips is exactly where the contact with the rear screen occurs. Is there any 'fix' for this aside from wrapping that section of the exhaust?

BTW, did you happen to be in Coalinga this past weekend? I thought I saw you or someone that looked exactly like you.
 

BlackICE

GT Owner
Nov 2, 2005
1,412
SF Bay Area in California
Bill, thanks for your input. That bend right before the tips is exactly where the contact with the rear screen occurs. Is there any 'fix' for this aside from wrapping that section of the exhaust?

BTW, did you happen to be in Coalinga this past weekend? I thought I saw you or someone that looked exactly like you.
You have an eagle's eyes, he was there.