Sandblasted headers: spray or leave?
 

Hi there,
as I wanted my exhaust manifolds to be crackfree, I had them samdblasted. The results: no cracks. Yay! But now: should I spray the headers? I would eypect that they are made of either iron or steel, but more so cast iron... So it'll take a few decades before they are really shite...

As you barely see the headers on the V12, I don't want any fancy colours there - no reason. So would it make sense to spray the parts? If so, what would you use?

Cheers

Damien

PS: how hot do these parts get on a catfree engine?

More than likely plain old cast iron. High temperature coatings do exist.
But, nothing is forever... Ceramics are the most elegant. Powder coating might last a while as does "header paint".


I'd leave them be. They will rust under the high temperatures to a nice red oxide color. They will outlast most of us by a century or more...


Carl

Ceramic coating are long lasting and look great

There are thermal coatings which help to reduce engine bay temps which might be worth looking into.

I doubt they'll rust away... I was tempted in painting them but they weren't like that from the factory. Would it be worth doing the downpipes? Or even wrapping them wirh the exhaust heatshield wrap stuff?

I seem to recall that wrapping cast manifolds could cause them to crack. You might want to research that a bit.

EDIT - Not an expert, and this is from memory, but I think you can thermal coat cast manifolds because they do the inside and outside of the manifold, but if you just wrap the outside it causes problems.

I would only wrap the downpipes...

I treated the manifolds on my XJ6 with phosphoric acid. Removed the rust off and leaves them with a beautiful clean metal look. The coating this deposits on the iron remains rust proof. Not tested truly long term yet but they look sandblasted clean now four months later.

Disclaimer. Test yourself on an inconspicuous section. I am not a lawyer.

Have them Ceramic coated inside and out, this will have the added benefit of reducing under bonnet temperatures. It's not feasible to wrap them also wrapping steel can cause rust as the fiberglass wrap can get wet and if not driven to dry them will cause rust.

Not sure about their availability in Germany, but this is what you're looking for:

Jet-Hot High Performance Coatings

I used Swaintech White Lightning Thermal Barrier Coating on my Manifolds. It is .015" thick, but they can only do the outside as they have to plasma spray it on. I also have had my heatshields and downpipes coated with Jet-Hot, they can do inside and out of pipes. Jet-hot is about half the price of Swaintech. The Swaintech is a really thick coating and the Jet-hot is about the thickness of paint. Both of them look great, and I believe have their uses. I couldn't get the chrome like finish on the heatshield as they run it through a ceramic tumbler and JET-HOT was concerned it would dent up or bend the heatshield. So I went with the silver non polished finish and makes it look more OEM like finish (which is what I am going for) plus I won't have to ever worry about it getting rusty or peeling, as they have a lifetime warranty. Both companies sandblast the parts prior to applying the product.






In summary (note some of these are my opinions):


Swaintech:
2x the cost
Not particularly "pretty", but not ugly as they use in their marketing.
Excellent at keeping heat inside.
Only can be done on the outside of parts
Very Thick .015"
Only comes in the white color
Conversation Starter: When people see this coating they ask we what it is as many have not seen it before.
Coating appears similar to the coating we apply to Gas Turbines/Jet Engines which are designed to prevent exotic nickel based super alloys from melting.


Jet-Hot:
Half the price of Swaintech
Can be in any color and be polished up like chrome
Inside and outside of parts
States it reduces underhood temps, but I don't think as much as swaintech.
Thickness similar to paint
Prevents Future Corrosion
Lifetime Warranty


Both are great products and you can't go wrong with either of them.


On my XJ6 I tried painting the heatshield with all sorts of high temp paints in the 1,000F + range. They all failed and started peeling where the exhaust manifold touches the heatshield.

My somewhat fanciful suggestions for exhaust system enhancement are:

Standard

https://cimg3.ibsrv.net/gimg/www.jag...2f2a67f6a8.jpg

Improved


https://cimg9.ibsrv.net/gimg/www.jag...8d2261a0df.jpg


https://cimg0.ibsrv.net/gimg/www.jag...e431367942.jpg


https://cimg3.ibsrv.net/gimg/www.jag...592e8d8d97.jpg



https://cimg5.ibsrv.net/gimg/www.jag...81bdcc7e83.png

Since you've gone to all the trouble to remove the manifolds and cleaned them up, it seems a shame not to get them thermal coated. You are going to go through so much work to bring the engine up to snuff, and engine bay temperatures are going to accelerate the deterioration of all your hard work.

Just food for thought. Good luck.

Another thing you can do with the exhaust manifolds is to clean up the casting imperfections inside. Allen Scott from TWR wrote a section about this in his book and states they picked up quite a few ponies by cleaning up the inside of the exhaust manifolds.

Paul
Great pics. The one above looks very like an aftermarket job that Hayward and Scott sell, and Hyper used to. I have been quite unable to find out if such modified exhausts make any difference at all to the performance of the otherwise standard 5.3 HE engine. The manufacturers themselves have no dyno or other figures at all!
Do you happen to have any info or experience of them?
Greg

I'd love to do that and fit some fancy equal length headers but my goal is an original car and that means standard headers... :(

my thermal ceramic coated exhaust manifolds , perfect condition 21 years and holding!

also it does lower under hood temps, some, maybe 30%.

i bead blasted them, then port matched , and had them coated by Swain tech,NY., inside and outside.

also had my cylinder heads coated ,the flat head surface and(most important) the exhaust ports,(dont want much heat getting to the coolant jackets).

there are pros and cons about coatings, but Swain is a hi-quality company!

and for cleanup,some WD40,rub it in,when cold engine, been about a year for what you see!

Hi Greg, you're correct this replacement exhaust header is manufactured by Hayward & Scott, it's available built to order. Versions listed for V12 E type or XJ12 (their advert doesn't specify XJS but I would expect they can provide same.
Not inexpensive, approximately £1300 to £1400.

I don't have any personal experience of this or any non standard V12 exhaust and can't comment on performance other than speculation.

With standard cast iron "log" style exhaust manifold the design is all about ease of manufacturing, I.e producing sand cast mold.

It's difficult to believe tubular manifold can't improve on exhaust flow characteristics of cast item. As I am sure you're aware improved flow can lead to better exhaust scavenging and consequent improvement in cylinder filling. Any such improvement in volumetric efficiency leads to more potential power output, assuming combustion efficiency is not reduced and extra air flow has appropriate fuelling increases.
Some exhaust designs seek to utilise pulses to enhance scavenging of other cylinder on same manifold but these effects are usually variable with rpm and due to resonance effects gains in one part of rev range sometimes have losses at other parts in rev range and will interact with valve timing, especially valve overlap.

Whether any increases in power on normally aspirated (non forced induction) V12 engine with alternative exhaust are significant to justify the cost I wouldn't be sure.

Apologies for thread digression.

TWR (Alan Scott) did a significant amount of R&D on the V12, and freeing up the intake and exhaust on the 6.0L V12 freed up about 30hp still using the cast exhaust manifolds. I think the main advantage of tubular are weight saving.

Exhaust scavenging works, but really is for high RPM power, at lower RPM ie under 5000rpm scavenging is almost useless, mainly due to the high valve overlap required and the lower exhaust gas velocity, this is what causes V8's with big cams to idle lumpy. I saw data on a Cup Car engine and the exhaust scavenging sucked 100" water at the inlet on overlap, this is more SUCK than the piston going down the bore can create, This was at 9000rpm.

TWR, according to A Scott, cut the cast manifolds down the centreline, cleaned them up considerably, then carefully welded them back together and disguised the join successfully!
Greg