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Question about exhaust manifold heat shields
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eche_bus
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PostPosted: Mon Mar 02, 2015 12:31 pm    Post subject: Question about exhaust manifold heat shields Reply with quote

How important is it for the thin metal and asbestos(?) that surround the exhaust manifold pipes to be intact? Here's mine:

Left side
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Right side
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The pipes and flanges seem good. No exhaust leaks detected before pulling the system apart. How important is the heat shielding? How should I go about restoring or replacing these? Are there new or NOS?
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Wildthings
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PostPosted: Mon Mar 02, 2015 2:17 pm    Post subject: Reply with quote

They seem to do a good job keeping the pipe from deteriorating from the outside in. Probably keep some heat away from the heads as well. Never heard of a good replacement though. Crying or Very sad
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aerosurfer
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PostPosted: Mon Mar 02, 2015 2:37 pm    Post subject: Reply with quote

On my bus and other header pipes i have sold and come across, i have not had any with the asbestos insulation. Even in the classifieds i have rarely ever seen a pipe with them. All else being equal, its the mating surfaces and especially the flanges that are the critical parts of those pipes.

Perhaps a good insulation idea 40 years ago, but IMO the pipes were over engineered and the insulation was underdeveloped.

I have both great heat and excellent head temps and AFRs out if my stock (to the muffler) system
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gliderman
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PostPosted: Mon Mar 02, 2015 2:47 pm    Post subject: Heat shields Reply with quote

I have a '79 Calif. emissions westy with the stock exhaust system. The left-side exhaust manifold had a heat shield that was similarly deteriorated. I assume that it is there to keep head temps down since the manifold runs directly below the head on the Calif emissions setup. At rebuild time a few years back, I remove the old heat shield and wrapped the manifold with manifold insulating wrap that you should be able to find at your local auto parts store. I secured this insulation using steel mig-welding wire wrapped around the manifold every inch or so. Many years later, it is still in place and I have some peace-of-mind knowing that I am not frying my heads with a the red-hot manifold an inch or below.

T

'79 westy
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Bleyseng
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PostPosted: Mon Mar 02, 2015 5:38 pm    Post subject: Reply with quote

It was stock but almost every set of J tubes I have seen its been rusted off. That being said [email protected] had a good complete set a month ago laying there in the garage.
It's not a big deal as hot air is blasting over the J tubes from the heads pushing the heat away. I don't think it does much to keep the heat from the J tubes from heating up the heads Wink
Maybe it was to try and keep the J tubes as hot as possible so the exhaust going into the HE's was Hot Hot Hot.
I switched over to the 72-74 HE setup as it's much simpler and doesn't rob HP like the later setup. ( about 5hp on a 914).
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aerosurfer
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PostPosted: Tue Mar 03, 2015 5:42 am    Post subject: Re: Heat shields Reply with quote

gliderman wrote:
I assume that it is there to keep head temps down since the manifold runs directly below the head on the Calif emissions setup.


Secondary effect perhaps, but likely just the opposite; to keep exhaust temps UP, for continued gaseous burn and breakdown as it flowed through the system

gliderman wrote:
Many years later, it is still in place and I have some peace-of-mind knowing that I am not frying my heads with a the red-hot manifold an inch or below.


This is incorrect. Remember VW had to go to this design because of emission regulations. Its been proven over and over the 72-74 style design was more efficient for power (claimed for heat as well), but they couldn't keep what came out of the tail pipe clean enough as the rules got more stringent.

The 75-78 style was adopted to increase the total burn time of the exhaust gas before it reach the cooler area of the muffler and out the back as CO. A perfect world burn would produce Hydrogen and Oxygen only. Eventually with a CAT added and the overly complicated 79 Systems. IE the slow death of the aircooled engine Sold in the US.

The exhaust pipe is not 'red hot frying your head' That is by design. Think about it, since the original heater boxes went straight down and out into heater boxes under the head as well. The cooling tins, ducted airflow and metal to metal heat distribution on the head itself, as well as timing and mixture control is what keeps your heads cool or fries your Valve guides
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eche_bus
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PostPosted: Tue Mar 03, 2015 1:11 pm    Post subject: Reply with quote

Wouldn't the Exhaust Manifold insulation/shield both keep temps inside the pipe up AND reduce its heat radiation up into the head? At idle, doesn't the EGR valve lean the fuel mixture, raising exhaust temps somewhat in a situation where there is little airflow over the exhaust manifolds?

Also, if the shielding was there to help reduce emissions, couldn't it be argued that removing it would make it harder to pass emission tests? I've never seen anyone say so, just making a logical extension to the original claim.

Still, if many others have run these bare without elevated head temps AND without emission problems, I'm more than willing to consider doing that. I saw one thread here where a guy ceramic coated them, and that could be a good compromise.

gliderman - I've seen a lot of bad comments about wrapping manifolds. Are you certain it's not rusting out the pipes?
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Wildthings
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PostPosted: Tue Mar 03, 2015 2:00 pm    Post subject: Reply with quote

eche_bus wrote:
Wouldn't the Exhaust Manifold insulation/shield both keep temps inside the pipe up AND reduce its heat radiation up into the head? At idle, doesn't the EGR valve lean the fuel mixture, raising exhaust temps somewhat in a situation where there is little airflow over the exhaust manifolds?

Also, if the shielding was there to help reduce emissions, couldn't it be argued that removing it would make it harder to pass emission tests? I've never seen anyone say so, just making a logical extension to the original claim.

Still, if many others have run these bare without elevated head temps AND without emission problems, I'm more than willing to consider doing that. I saw one thread here where a guy ceramic coated them, and that could be a good compromise.


It would be hard for much radiant energy to get deep into the fins on the heads. There would be a measurable increase in heat, but just not very much of one.

The EGR valve does not lean the mixture, it just lets mostly inert exhaust gases into the intake charge (leaving the mixture unchanged), thus lowering the maximum temperature seen in the cylinders.

Can say as far as emissions are concerned, this would be an interesting theory to test.
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PITApan
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PostPosted: Tue Mar 03, 2015 6:07 pm    Post subject: Reply with quote

eche_bus wrote:
Wouldn't the Exhaust Manifold insulation/shield both keep temps inside the pipe up AND reduce its heat radiation up into the head? At idle, doesn't the EGR valve lean the fuel mixture, raising exhaust temps somewhat in a situation where there is little airflow over the exhaust manifolds?

Also, if the shielding was there to help reduce emissions, couldn't it be argued that removing it would make it harder to pass emission tests? I've never seen anyone say so, just making a logical extension to the original claim.

Still, if many others have run these bare without elevated head temps AND without emission problems, I'm more than willing to consider doing that. I saw one thread here where a guy ceramic coated them, and that could be a good compromise.

gliderman - I've seen a lot of bad comments about wrapping manifolds. Are you certain it's not rusting out the pipes?


It definitely rusts the pipes. I've seen it and on ceramic coated pipes as well (poorly coated---they were my pipes BTW). Keeping wrap spray on it helps some but not much. In the wet the wrap keeps a layer of steam right on the hot pipe. Rust city.

Notice how the tinwork on heater boxes rusts most where it contacts the actual manifold pipes? That is just elevated temps and daily air/moisture. It's the heat that's the big catalyst. Add a jacket that holds moisture and you're scrued.


if the pipe is cheap and easy to replace, then take advantage of the insulation. if not, avoid it. It's for racers who need to maintain exhaust temps and gas velocity in the pipes. The racer lookalike poseur wannabees put it on to hide the rust they got and/or to look like real racers.
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Hoody
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PostPosted: Wed Mar 04, 2015 8:04 am    Post subject: Reply with quote

Properly applied ceramic coating inside and outside the pipes is the way to go once the outer shield has been removed. It will reduce the heat much better then the original asbestos and outer sheet metal skin and there won't be a sponge to hold moisture there.
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aerosurfer
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PostPosted: Wed Mar 04, 2015 8:40 am    Post subject: Reply with quote

Its the internet, we can argue and hypothesize til someone starts with the cat pictures and the thread gets locked...

The whatever your thoughts on the collars are, the key components of these parts are the ends. Good torque and sealing to the head, which is well documented, and keeping the other flange sealed and preventing the bolts from rusting to them. If all the rest of your tin is in place, the header F-pipe also has the advantage of mostly not being subject to direct weather elements, and because of its job and temperature, if you are using the engine, its gonna be dry on there.

John,

You haven't shown us any pics yet of the U bend pipes. Those were also originally insulated. None of mine or any I have sold or scrapped had anything left of the original. Its gonna be the ends that are the factor if they are scrap or re-usable.

My U-bend pipes and heater boxes are covered in VHT paint and have held up well in the first 4k+ miles and 2 years.
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PostPosted: Wed Mar 04, 2015 10:59 am    Post subject: Reply with quote

eche_bus wrote:
Wouldn't the Exhaust Manifold insulation/shield both keep temps inside the pipe up AND reduce its heat radiation up into the head? At idle, doesn't the EGR valve lean the fuel mixture, raising exhaust temps somewhat in a situation where there is little airflow over the exhaust manifolds?

Also, if the shielding was there to help reduce emissions, couldn't it be argued that removing it would make it harder to pass emission tests? I've never seen anyone say so, just making a logical extension to the original claim.

Still, if many others have run these bare without elevated head temps AND without emission problems, I'm more than willing to consider doing that. I saw one thread here where a guy ceramic coated them, and that could be a good compromise.

gliderman - I've seen a lot of bad comments about wrapping manifolds. Are you certain it's not rusting out the pipes?


Insulated u-tubes and manifolds were initially required to help get the catalyst up to temperature as quickly as possible.

I did a test of running my engine with non-insulated pipes up until August 2011, then insulated manifolds and u tubes after. The insulation actually does help reduce surrounding engine temperatures. I did not see a discernible difference at the CHT gauge. The pipes themselves are rust free stainless, but their flanges are prone to rust,
Colin

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eche_bus
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PostPosted: Thu Mar 05, 2015 3:46 pm    Post subject: Reply with quote

Thanks to all for all the very useful input. Colin, I especially thank you for the research-based comment. Catalyst temperature ... now that makes sense.

aerosurfer wrote:

John,

You haven't shown us any pics yet of the U bend pipes. Those were also originally insulated. None of mine or any I have sold or scrapped had anything left of the original. Its gonna be the ends that are the factor if they are scrap or re-usable.

My U-bend pipes and heater boxes are covered in VHT paint and have held up well in the first 4k+ miles and 2 years.


The U-pipes seem to be in real good shape. Solid heat shields, no cracks or breaks.
Image may have been reduced in size. Click image to view fullscreen.


It's kind of hard to tell about the flanges as they still have fragments of gasket attached to them, but nothing was crumbly. They feel solid. Would you or others agree that a file should clean these surfaces up? It's probably real hard to tell from pictures.
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Tcash
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PostPosted: Thu Mar 05, 2015 4:41 pm    Post subject: Reply with quote

A file would work.
If you know someone at a machine shop you could have them milled?

Good Luck
Tcash
P.S. I would ceramic coat.
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PostPosted: Thu Mar 05, 2015 5:07 pm    Post subject: Reply with quote

a large flat belt sander with aluminum oxide. Used to sand manifolds flat all the time that way. They have heat worked from all the heating and cooling cycles. A file is really hard to work them with compared to a large belt sander with a plate behind it. Sand 30 - 45 degrees to the right, 30 - 45 degrees left rotate 180 and do again.
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PostPosted: Thu Mar 05, 2015 5:26 pm    Post subject: Reply with quote

Those ones look in great shape! Lots of metal on the flanges. What they said above.

Mine were thinner, and warped, took a lot of filing and heat and hammering to get them flat. Use the thicker exhaust gaskets, the ones with the little hole perforations, there is more crush to them than the thin Reinz ones. Seal them up with some copper High temp RTV and you are good to go.
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PostPosted: Thu Mar 05, 2015 6:12 pm    Post subject: Reply with quote

I have belt sanded them and then flat sand them by putting a sheet of sandpaper on a piece of glass. Then sand them dead flat which you can use Prussian Blue to check your work.
If you have a soda blaster it works great to clean them up.

I traded out my set of late exchangers to someone who needed a good set.
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PostPosted: Thu Mar 05, 2015 7:16 pm    Post subject: Reply with quote

You can scrape any lose gaskets and do nothing else. Skim them with muffler paste and assemble with ordinary gasket (paste on both sides of gasket. Fer crissakes, it's an exhaust system not a head joint!. The thing is dumping into open air 2 feet away.
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eche_bus
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PostPosted: Fri Mar 06, 2015 10:07 am    Post subject: Reply with quote

OK, got a good sense for this now. New territory for me, so thanks again to all that helped by sharing their perspectives and opinions.
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