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chevynut
03-24-2015, 11:26 AM
I have a header to bumper stainless exhaust system all TIG welded together from straight pipe and mandrel bends. It's a long system with an x-pipe, and I've always wondered if I should have a pair of these in the pipes to try to isolate engine movement from the rest of the system. Do you think I need these?


http://static.summitracing.com/global/images/prod/mediumlarge/vpe-63004_ml.jpg
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MP&C
03-24-2015, 03:05 PM
Are they on the new Vette's? If your system is rubber isolated and has room for movement I wouldn't worry. If it looks like you may experience some noise due to exhaust in close proximity to frame members, it may be a good idea.

chevynut
03-24-2015, 06:19 PM
Thanks Robert. My exhaust currently has rubber hangers but I'm looking to replace them with some billet ones with urethane isolators to make it a bit more rigid. It can still move, though. I have urethane engine mounts so the engine shouldn't move too much. My concern was the length of the pipes that are all welded together, and the stress on the welds. I don't want it cracking.

Rick_L
03-24-2015, 07:13 PM
If your hanger system allows some axial movement you're good. When things get constrained - well then something has to give.

They are done both ways, as well as some other variations.

You can calculate the added length, I don't think it's that much because the pipe is only hot up by the engine.

chevynut
03-25-2015, 12:04 PM
Rick, with most of my exhaust being stainless it will expand almost 50% more than if it was steel (9.6 in/in/F versis 6.7 in/in/F). I thought those coupling bellows were for vibration, but maybe they're for expansion.

My first hangers will be 32" from the header collectors which are about 2 feet from the center of the engine. If I assume the exhaust cools from around 1200F at the port to 600F in that distance, it should expand about 3/8" at the first hanger. That's a lot imo. Now if we assume the rest of the ~7 feet of pipe drops to 200 degrees at the exhaust tip you get another ~1/4 of an inch expansion. That's 5/8"!!! Are these temps reasonable?

So how do guys get away with bolting their exhaust with hangers that don't allow for this much axial expansion? I see it all the time.

I'm thinking that I need to make these billet hangers slide on some studs rather than bolting them solidly in place even with the urethane bushing.

http://www.deedsengineering.com/cms/wp-content/uploads/2013/07/N-3-white-190x243.jpg

NickP
03-25-2015, 12:40 PM
http://pic20.picturetrail.com/VOL1600/2283636/23877721/405578889.jpg

Rick_L
03-25-2015, 12:53 PM
I think your temperatures are a good guess for peak temps, but normal temps would be down quite a bit from that.

If you cut your expansion estimates by about 1/2 to 1/3, now you're getting into things that are more manageable.

rockytopper R.I.P 5-13-2017
03-25-2015, 01:17 PM
http://pic20.picturetrail.com/VOL1600/2283636/23877721/405578889.jpg

Those look awesome Nick. Were does one acquire them?

chevynut
03-25-2015, 01:37 PM
Nick, how does that system deal with expansion of the pipes the way you have it bolted up?

Rocky, look here: http://www.deedsengineering.com/

I just ordered some myself. :)

NickP
03-25-2015, 05:12 PM
There are a total of 8 Deeds clamps.

Rick_L
03-25-2015, 06:00 PM
I wonder how much compliance you get with their bushing? How hard is it?

Some neat looking, and expensive looking, stuff. I don't see a whole lot of total solutions on the website, but there's certainly some things you could work with.

chevynut
03-25-2015, 09:01 PM
There are a total of 8 Deeds clamps.

I calculated about 1/2" or more of expansion which would seem like it would pop the urethane bushings out of the hanger at the bumper. I think rather than bolting them solid they should slide on a shaft. Did you use any expansion joints?

chevynut
03-25-2015, 09:14 PM
I think your temperatures are a good guess for peak temps, but normal temps would be down quite a bit from that.

If you cut your expansion estimates by about 1/2 to 1/3, now you're getting into things that are more manageable.

Yes I was thinking peak temperatures which COULD occur if a guy did any hard driving. But even at half those temps we still get 5/16" or expansion which seems like it would pop the bushings out of those hangers, especially at the bumper where the most movement occurs. The other problem is stainless has about 1/3 the thermal conductivity of steel, so it dissipates less heat and traps more in the pipes. The hotter they are, the more they expand.

I wonder if theres's any empirical data on the expansion of a stainless exhaust system that's 10 feet long.

I ordered 4 of those Deeds Engineering clamps and I think I'm going to put them on smooth rods or long bolts so they can slide a bit as the pipes expand. IMO there's no reason to bolt them down and it will just cause stress in the system and hangers.

chevynut
03-25-2015, 09:35 PM
I just found a site that gives the thermal expansion coefficient of 18/8 stainless at elevated temps. From 32-600F the mean expansion is 11.8 in/in/F (even higher at higher temps). That means I under-estimated the expansion of the exhaust quite a bit since I used 9.6 in my calculations above. If I assume a mean temperature of 400F as above, the expansion is 9/16" in 10 feet, not counting the headers. It looks to me like overall expansion could be as high as 3/4" at peak temps, and even 3/8" or so at more normal operating temps.

Just think what would happen if it looked like this!!!

http://www.epi-eng.com/images/Engine/exhaust_technology_01.jpg

chevynut
03-25-2015, 10:40 PM
I wonder how much compliance you get with their bushing? How hard is it?

Some neat looking, and expensive looking, stuff. I don't see a whole lot of total solutions on the website, but there's certainly some things you could work with.

The hangers aren't too bad at $50 each imo. I've seen similar ones for $65-70 each.

I really don't think it matters much how hard the bushing is. If you look at it and how it's bolted on, I think there's very little compliance axially if bolted solid to the frame. The bushing doesn't have much wall thickness either, so it doesn't really isolate the exhaust from the frame that well. I'm using them because I need more support at the bumper, and I don't have a lot of room at the transmission mount.
http://www.deedsengineering.com/cms/wp-content/uploads/bushing-kit-190x243.jpg

Later, during final assembly, I hope to replace my rubber isolators at the shock crossmember with something like this...I may have to make them myself to get the right length. And I won't bolt them solid, they'll just have rods through them with something to keep them from coming off:


https://scontent.cdninstagram.com/hphotos-xaf1/t51.2885-15/e15/11015679_554011661405392_1131108091_n.jpg

carls 56 (RIP 11/24/2021)
03-26-2015, 05:45 AM
I'd have to go back to college to understand half of what you have been talking about. ain't going to happen. :eek:

chevynut
03-26-2015, 07:51 AM
Carl, all I'm saying is that when the exhaust system heats up it expands toward the rear bumper. If you clamp the pipe with a hanger, that hanger has to be able to move, flex, or somehow account for that expansion. The calculations were just to show the amount of expansion you could get.

NickP
03-26-2015, 09:20 AM
I really don't think it matters much how hard the bushing is. If you look at it and how it's bolted on, I think there's very little compliance axially if bolted solid to the frame. The bushing doesn't have much wall thickness either, so it doesn't really isolate the exhaust from the frame that well.

There is more movement in them than you may be aware of. Don't ask me how much though.

chevynut
03-26-2015, 10:09 AM
Nick, do the hangers clamp solidly to the exhaust pipe, or can the pipe slide in them? I seriously doubt there's 3/8" of compliance in one of these hangers if they don't allow pipe movement. There are ways to address the pipe expansion using them, though.

Rick_L
03-26-2015, 11:10 AM
Seems to me those hangers are better suited to using the flexpipe to deal with the movement.

chevynut
03-26-2015, 11:20 AM
Seems to me those hangers are better suited to using the flexpipe to deal with the movement.

I agree, but I think you'd have to put more than one flex-coupling in the system. I think a non-rigid mounting does the job better.

Troy
03-26-2015, 11:45 AM
How about mounting using the hangers you've shown and align axially. This would allow movement from expansion. See 3D model below.

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NickP
03-26-2015, 12:13 PM
Nick, do the hangers clamp solidly to the exhaust pipe, or can the pipe slide in them? I seriously doubt there's 3/8" of compliance in one of these hangers if they don't allow pipe movement. There are ways to address the pipe expansion using them, though.

No, Lazlo once the clamp aspect of the unit is tight the tube will not move inside of it. But there is a lot of movement (not sure of 3/8") in the unit.

chevynut
03-26-2015, 12:30 PM
Troy, that's a good way to deal with it. I plan to just hang them like my rubber ones and allow them to slide. if a guy placed the rod ends facing each other with a good overlap, they could never come off.

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What we're discussing is the ridid mount ones and how to make them work. I'm trying to deal with what I think is too much side-to-side movement at the bumper hanger using my rubber mounts. I plan to use the Deeds hangers and put them on a rod so the pipe can expand and contract. I know there are rubber hangers with 3 holes, but I have read that these eventually start sagging and I don't want that.

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Rick_L
03-26-2015, 02:29 PM
Duh Troy, why didn't I think of that?

chevynut
03-31-2015, 09:29 AM
Here's how I decided to address the exhaust pipe expansion. After getting them and looking at them, I feel that the Deed's Engineering hangers provide little or no compliance in the system when clamped to the pipes. The bracket and rod are stainless.

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