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Old 07-27-2011, 11:48 PM   #1
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Default Discuss: Slip Joints vs. flex tubing

So after working with the slip joints on a begi setup, and doing some basic searches on google, I haven't been able to conclude why anyone would want to use a slip joint.

I know that people say race teams have been using slip joints with springs as the industry standard, and i see some very accomplished fabricators using these joints on top end cars, such as agtronic seen here:

http://www.honda-tech.com/showthread...267900&page=54

I just don't understand for the life of me why someone would choose to use slip joints over flex joints and v-bands. I've built several exhausts now, so i understand the pros and cons of various clamping systems, but its hard to think of a situation where slip joints would be the best choice.

If anyone has any input on slip joints and their purpose, please shed some light on the situation. Cheers.
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Old 07-27-2011, 11:55 PM   #2
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I would assume for space reasons. But I agree, I do not like slip joints either.
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Old 07-28-2011, 12:12 AM   #3
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Here's a Ferrari F1 header. Inconel 625 at least partially, most likely.

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Old 07-28-2011, 12:24 AM   #4
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Easier assembly, and dis-assembly. It also has room for some play. My FF car has slip joint headers.
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Old 07-28-2011, 12:27 AM   #5
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F1 above is irrelevant to mere mortals.


I have flex. It's held up for .22 miles on the V8 car. That's about all that I can say about that.
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Old 07-28-2011, 07:35 AM   #6
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Quote:
Originally Posted by Bond View Post
Easier assembly, and dis-assembly. It also has room for some play. My FF car has slip joint headers.
That couldn't be further from the truth at least for the disassembly. I've got a Y-pipe in my v8 swap and have 2 2 1/2 v-bands up front and a 3 inch v-band in the back and can install and drop in 3 minutes. Prior to the v-bands I had slip joints and they were a pain to remove. You need space to slide the ends apart and disassembling slipjoints gets tough if you're in an area with any moisture.

Obviously on a tight clearance header setup a v-band is not practical though.
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Old 07-28-2011, 09:53 AM   #7
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Takes me about 10 seconds to pull off the spring and it slides out. Use PB blaster if you are a weak bitch.
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Old 07-28-2011, 10:34 AM   #8
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Slip joints and flex bellows have different purposes. The slip joint in a manifold allows for thermal expansion without distortion, relieving stess off solid, welded joints. A thin wall turbo manifold would otherwise be prone to cracking.

Slip joints on a downpipe only serve to join two pieces together. Like v-bands, they don't have any give.

Flex joints allow independent movement, to some degree, of either end of the joint. Without a flex bellow in the DP, there's 10ft of leverage wreaking havoc on the the manifold studs.
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Old 07-28-2011, 03:33 PM   #9
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So, a slip joints purpose is to fit into tight spaces, usually on thin wall headers that need some room for thermal expansion.
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Old 07-28-2011, 03:41 PM   #10
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Great thread and very important (to me as well) question.

I have a little follow up question: how well do slip joints seal in a pressurized environment? A manifold will get pressurized pre-turbo, wont a slip joint be more prone to letting some of said pressure out? Or is that ONLY if its faulty/defective?
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Old 07-28-2011, 03:47 PM   #11
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Use a double slip if there is pressure. this type has a lower tendency to leak and will seal properly if fabricated correctly.
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Old 07-28-2011, 07:07 PM   #12
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Quote:
Originally Posted by shlammed View Post
Use a double slip if there is pressure. this type has a lower tendency to leak and will seal properly if fabricated correctly.
+1. Timmy catches **** because the double slips in his AF setups are a little overkill (typically they're used for pre-turbo manifold connections) but they don't leak. The double-slip on my EWG connection does provide a tiny bit of play to take the stress off of the welds, but Tim uses a baller 1.5" Vibrant flex joint there instead now.

V-bands are great for pretty much everything but double slips are better in tight spots. Proper double slips also use springs to maintain preload on the slips to prevent leakage while allowing for thermal expansion/growth.

Check out the last photo from your example:


V-bands wouldn't be possible there, so (presumably) double slips and springs are used. Ideally the collector would have been an integral part of that manifold, but the fab bill for that would be pretty astronomical.
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Old 07-29-2011, 02:09 AM   #13
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Double slip joints are the standard for VERY high end race teams from nhra prostock drag cars to a lot of nascars. They are mainly used on the header to collector connection and a major benefit of them to the engines are their flow characteristics. These race teams go to the nth degree to squeeze every last drop of power out of the engine and the exhaust is not overlooked. Their exhausts are made out of 321 stainless and lower classes will sometimes use 304 stainless. Inconel is very expensive and very difficult to work with, if you can find any but it is by far the strongest/retains most heat. The reason for stainless is because it retains more heat inside each individual tube and therefore scavenges better. You need to use a similar material with almost identical heat properties for the joints and thats when the double slip joints come in. They dont leak, they expand/contract at the same rate at the header/collector, they have quite a bit of fore and aft flexibilty but no vertical movement whatsoever(they arent supposed to). Vbands are great but they disrupt the flow plus who would use 4 vbands from a header to collector lol. On our cars, vbands, flexies and all the others work fine.
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Old 07-29-2011, 02:14 AM   #14
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Quote:
Originally Posted by Savington View Post
Ideally the collector would have been an integral part of that manifold, but the fab bill for that would be pretty astronomica
No high end car would want the collector as part of the header, because they usually go through 3-4 different combos of headers/collectors on the dyno and use different collectors for varying conditions at the different tracks.
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Old 07-29-2011, 02:02 PM   #15
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Related i guess: My begi dp leaks at the slip joint. Im at least 15 kinds of mad. It seems to leak less when the car warms up.
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Old 07-29-2011, 04:03 PM   #16
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Agrtonic makes some pretty stuff, and they were nice enough to talk to me on the phone about issues with the TiAL turbine housings...but they could learn a few things from this forum.

Quote:
Originally Posted by Jpopsbronco View Post
Double slip joints are the standard for VERY high end race teams from nhra prostock drag cars to a lot of nascars.
Most of us are running our cars hard enough that we need them too.
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Old 07-29-2011, 04:14 PM   #17
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i havent read all of the post but the mane reason for slip joints is movement under engine torque. Apposed to the engine moving the entire welded/v-banded/etc exhaust system when the car twists the chases off the line (FnF quote for anyone who got it) it allows just the header to move, very similar to a flex pipe.

Good read with similar concept:

edit: they deleted one of my favorite links on the interwebz
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Old 07-29-2011, 04:16 PM   #18
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Quote:
Originally Posted by hustler View Post
Agrtonic makes some pretty stuff, and they were nice enough to talk to me on the phone about issues with the TiAL turbine housings...but they could learn a few things from this forum.

Most of us are running our cars hard enough that we need them too.
He (agtronic) is an amazing fabricator, but he has had some serious trouble getting enough steady work and is only working night hours in the shop now.

Aside from that, i dont think theres a "very tight" location on our cars that need a slip joint. I dont buy the "disrupting flow" bullshit, because the high end v-bands have recesses to perfectly fit eachother (vibrant) . It does make sense to me that its easier for swapping out different collectors on drag cars though.
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Old 07-29-2011, 04:29 PM   #19
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TiAL = high end v-band

I have a couple vibrant v-bands in my car and they really suck without a groove.
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