ABA 2.0 Swap; Cat Support Questions. PICS

[Vanagon Nut]

Hi everyone.

This is for a "diesel Vanagon" type exhaust with a "toilet bowl" aka Mk2 flex joint.

Is the "solid" support I made between the pre cat primary pipe and isolated diesel outer bracket a bad idea? If so, why?

Reason for installing the support; help keep engine vibration from causing the pre cat pipe to "wiggle".

The clamp at pipe was held closed with pliers while the nuts on rod were alternately turned the same amount. (avoid pushing/pulling the clamp at rod. Doing so might introduce stress)

I debated mounting a "softer" support between this pipe and body, then thought to mount the support to a metal-rubber hanger at the engine, but the 1.9 WBX, turbo diesel, some Subaru swaps, show a solid support in the exhaust system so I took that route.

The rod is small, was originally meant for the type of metal-rubber hanger shown below but if this added support causes something to break, I'd rather it be the rod and not the cat. (the rod would be the "canary in the coal mine" so to speak)

view from driver side

looking up

I have a square version of this

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1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[82westyrabbit]

Hi Neil. I think that that rod will be to flexible to help much with cracking. If nothing else I would add another rod to make a triangle from the bottom to out near the muffler hanger. Just my thought do with it what you want. John

[Vanagon Nut]

Thanks John. I agree that the support is not very strong. One reason I made it that way was that if vibration does make that pipe "wobble", that vibration might break the support before causing a failure elsewhere in the exhaust. e.g. at the cat inlet.

Since the support is attached to a pretty much isolated exhaust system, and not directly to the engine, a stronger support may not do any harm.

My initial concern was that even though the support is attached to an isolated exhaust, if it was quite strong, it might impart more vibration from engine to that pipe and/or not allow the metal to expand and contract during heat cycling.

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[82westyrabbit]

That’s good thinking of course. Are you just trying to stop vibrating or give it some support? John

[Tbob]

Neil, cracking exhausts, as you know, were one of the re-occurring issues with the inline engine conversions. When I built my conversion, I did a lot of research, and the question that I forget is where did they generally crack? I don't remember it being the cat in any case, but my memory is really not what it was. So, I may be forgetting. But it seems like the focus of your support is to protect the cat from being cracked,which is a noble cause. But IIRC, the exhaust pipes were cracking somewhere along the short distance between the header and the cat. So, if all that was true (and it has been 10 years since I did mine, so I may me just remembering poorly) then your brace, if strong enough, cuts the effective length of the part that normally breaks( the pipe between the header and the cat) in half. The problem was the rigidity; and the engine vibration(in a longitudinal axis), and your heavy exhaust(cat and muffler) on an axis perpendicular to the source of the vibration. IIRC, the problem was minimized by adding flexibility(adding a braided flexible coupling to the pipe between the cat and the header. Since what you are doing is making it more rigid, and more prone to cracking. But maybe more prone to cracking on the pipe where it is cheap to repair.
So, when I was doing my conversion, I thought about exhausts. On a conventional front engine, rear exhaust, inline engine, you almost never hear of an exhaust cracking. Vibration along a longitudinal axis, flexible mounted exhaust. Throw the motor in sidewise, and you get cracks. Back in the day all sorts of things were tried, but the braided flex joint became the solution of choice, possibly due to low cost and least amount of fitment hassle.
So, on the conversions, and the diesel Vanagons, and even the waterboxers, we have the same issue. Longitudinal engine vibration, heavy exhaust perpendicular to that. I had my waterboxer exhaust welded a couple times, as have others.
The solution to me was clear, to run the exhaust forward, to the center of the van, and the return it to the rear. Long enough to spread the forces along a longer moment arm, and hopefully prevent cracking. So far, so good.
However, do I KNOW what I am talking about, engineering wise? No! But it makes sense to me, and it has been borne out in my one example. YMMV, and Good Luck!
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1969 Deluxe, owned since 1973
1973 Westfalia, owned since 1983
1980 Westfalia, watercooled conversion
1985 Westfalia, stock!
1986 Westfakia, Audi I-4 conversion
A couple of trucks and a couple of Jeeps

[Vanagon Nut]

[Vanagon Nut]

[metropoj]

Neil, in contrast I have 25k kms on my OEM TiiCo header. I had it high temp powdercoated last year.

It Only has the braided flex before the cat, the rest of the exhaust supported by FAS bracket setup at the start and end of the 1.9l muffler.

I have no cracks or issues so far .... I hope it stays that way !

My understanding in my case was that the earlier engines were running lean and were not cracking near the cat, but near the exhaust manifold outlet area. My hope was that the newer ECU would help alleviate some of the heat buildup and perhaps not affect the header like the earlier ones.

When 1.8t time comes I think I'll use a similar layout when a header gets built. I see most 1.8t builds similar in design.

BTW, thanks for taking the time on all your documentation and R&D during your processes, they are quite informative and thought provoking ...
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John.
86 TiiCo powered Westy.

[Tbob]

Neil, I think that the idea of keeping the exhaust light and centering the weight around the vibration center as much as possible is on the right track. That big muffler back there most likely sets up some sort of harmonic that cracks it at the weakest spot. I would think, based on your experience, that mounting it more rigidly to the engine only would be part of the solution. If that is the case, would a flex joint be counterproductive. And, does the diesel vibrate as much as the ABA? I know my 3B vibrates enough to make going over 55-60 a chore. If the diesel didn't vibrate as much, then all the factory engineering that we are attempting to duplicate may be for naught.
So, in thinking about it(and when I think it usually hurts my wallet!), if I was to follow the diesel vanagon type of exhaust, I would: seriously rigidly mount the lightweight muffler/cat as close to the centerline of the vibration source, and mount only to the vibratory source and not to the body or engine bar or anywhere that isn't rubber mounted with the engine) use a flex joint inline before the cat(although alternatively, close to the cat before the 90 into the cat would most likely work.
What I think I would be trying to achieve is a decoupling of the moment arm of the muffler /cat from the flex of the exhaust pipe/toilet bowl movement. Will it work? Don't know! I'm not an engineer, I just play one!
_________________
1969 Deluxe, owned since 1973
1973 Westfalia, owned since 1983
1980 Westfalia, watercooled conversion
1985 Westfalia, stock!
1986 Westfakia, Audi I-4 conversion
A couple of trucks and a couple of Jeeps

[Vanagon Nut]

[Vanagon Nut]

[ndorian]

My plan was to add a flex joint as soon as the down pipe aligns with the carrier bar and the add cat as soon as I clear engine mount then pipe out the back. So my only mount would be the drivers side engine mount with a custom made brace. That is why I was asking about adding a hanger or something somewhere else. I just think that is too much horizontal distance and it won't really support the cat.

[ndorian]

My plan was to add a flex joint as soon as the down pipe aligns with the carrier bar and the add cat as soon as I clear engine mount then pipe out the back. So my only mount would be the drivers side engine mount with a custom made brace. That is why I was asking about adding a hanger or something somewhere else. I just think that is too much horizontal distance and it won't really support the cat. So where Vanagon Nut put a rod, I would need to rely on a good brace.

[ndorian]

Sorry I cross posted by accident.