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Discussion Starter #1
With regular use, the underbonnet temperatures must get fairly high and I'm wondering whether it is worthwhile trying to insulate the exhaust headers. I've looked around the web and several solutions seem to exist. Two made of the same compound (thermo-tec) seem to be available - one is a wrap and the other a small 'blanket'. A third alternative would be a shield over the headers mounted somehow so it doesn't rattle. Apart from decreasing temperatures in the engine bay, keeping the exhaust gas temperature up would decrease the gas density and possibly improve the movement of exhaust gas out of the manifold and down the exhaust system. Does anyone have any ideas or comments?
It's a slow Thursday downunder ......
Chris
 

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Certainly worthwhile trying to get temps down.

It'll help cut down on heat soak (more of an issue with EFI) and keep the clutch and brake fluid cooler.

I went with the shield option by cutting an approriate bit of 16ga steel, adding some brackets to it w/pop-rivets and hoseclamping it onto the header tubes proper.

It stands off about a cm, and the temps under there are noticably cooler.

Works well and was WAY cheaper to do than wraps, paints or dips and can be moved to another set of headers at will without the expense of new wrap, paint or dip.....
 

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`61 Giulietta Spider, `65 Giulia Ti 1750, `69 GT junior 1600, `73 Spider 2000, `74 GTV 2000, `98 156
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I think you are actually worried about nothing-if under bonnet temperatures were anything to get worried about Alfa would have addressed it. There is that ceramic coating called Jet Hot that can be done (around NZ $250) which does act as a bit of a thermal barrier and improves gas velocity through the headers if you are particularly worried about under bonnet temps and seek a small improvement but I know from experience that on a bog std car you need a dyno to detect any difference in engine performance and normal under bonnet temps in one of these don`t effect either engine or braking performance -there is ample airflow into that engine bay when mobile.

Richard J

`65 Giulia , `69 GT Junior, `74 GTV 2000, `76 Alfetta GTV, `77 Alfetta GTV, `84 GTV6
 

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Chris, I would recommend you tape your headers with that fiber type tape and use metal fastners. You can get all this from summit racing among others. The benefits are lower engine compartment temps and also improved engine performance. You see, as you tape the headers, exhaust gases loose less heat and thus exit the headers at greater speed improving overall enging output. I have this on three of my cars and all have benefited from this setup. Enrique
 

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The Jet Hot coating works really well. I have a set of coated headers on my track car and the underhood temps are way cooler than uncoated (think 200+ degrees surface temp). The coating looks good, and doesn't easily chip or scrape off. If I ever get a set of headers for my car I will go this route without a second thought.

Will
 

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I also use Jet-Hot, and I'm really happy with the results. I have two sets of headers coated, and that's they way I'll always go... When investigating alternatives I was also advised by a team that prepares Alfas for the track against wrapping the manifolds or headers, but I can't remember what the issue was. I'll see if I can make a call to find out and then share the advise with the group...

Best regards,
 

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Discussion Starter #7
Thanks for the interest so far. I can borrow an accurate broad range digital thermometer with a remote sensor from work, so I might tape it around the engine bay and take some readings. I realise that the performance enhancement may be theoretical only, but as to the cooling, somewhere in the back of my head I had an idea that Alfa fitted some sort of exhaust manifold shield to their later model twin cams ? 1990s ? Spiders. I'll hunt around a bit and see what I can find.
Molto grazie,
Chris
 

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Discussion Starter #8
Got some results.
My car doesn't move at the moment (no wheels) so these will possibly be 'worst case' numbers. I taped the probe to the bell housing of the front brake booster then started the engine, adjusted the idle up to 1200rpm and closed the bonnet. After 10 minutes or so the engine had reached its operating temperature according to the water temp gauge. After a further 15 minutes the probe temp read a fairly stable 63.5degC (that's just over 146degF for you old fashioned Americans) though it was still edging up very slowly. That is fairly hot - I took some photos which I've attached. Interestingly, the outside bonnet temperature was about 37degC probably because I have no under bonnet insulation. These figures would be lower when driving and when I refit my wheels, after I sort the brakes, I'll try to get some numbers on the move.
Ciao,
Chris
 

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When investigating alternatives I was also advised by a team that prepares Alfas for the track against wrapping the manifolds or headers, but I can't remember what the issue was.
Premature failure of the tubes due to rot.


Chris1750 said:
I had an idea that Alfa fitted some sort of exhaust manifold shield to their later model Spiders
Yes, Series 4 had a shield.
 

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Chris: This is just my opinion but my decision to use header wrap would depend on what kind of exhaust manifold I was using. I've seen numerous cases of extractor type exhausts cracking after having asbestos header wrap installed. Unfortunately extractors (headers for my buds in the States) rely on heat disipating through the walls of the tube. When the heat is contained it causes a structural change and the material (steel) becomes brittle and they crack.

Now I've not seen anyone do it, but if you're running the standard cast iron exhaust manifolds, they may be able to handle the additional heat build up due to the different material used in their construction (cast Iron). I'm not a metalurgist so I can't say for sure, maybe someone out there can expand on that. I know for a fact the Jet Hot coating works very well and has no negative impact on the exhaust components (just the opposit in fact). Just my 2 cents worth, best of luck which ever way you go. Cheers, Rick.
 

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Discussion Starter #11
Thanks to all so far.
At present I'm just thinking about what is available and canvassing opinions.
The car is standard and is not used for racing/rallying. The exhaust manifold is zinc dipped cast iron connecting to a full stainless system - it makes a nice noise.
I've looked up the Jet-Hot website and it looks interesting. I'll probably have to remove the extractors at some stage, so I may send them to get coated.
Regards,
Chris
 

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Heat doen't disappear

You want to keep in mind that most of the items you have mentioned to lower the heat under the bonnet/hood do so by simply passing it along the line.


In other words, your exhaust system is going to take the heat. And so is your bodywork. Especially right by your feet.
 

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The exhaust wrap will rot the pipe as it is cast and the way the fiberglass traps the heat

Honestly for the amount you would spend on jet coating you might as well get stainless steel high flow collectors as stainless conducts 210% less heat than their cast counterparts. Plus you will get a real boost in HP.
 

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As mentioned in my previous post, I did follow-up on the advise I got form the team that prepares Alfas for the track against wrapping the manifolds or headers. It is because it will cause cracks. In this respect, it matches the comment by Ozalfaracer.

Best regards,
 

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GTA heat sheild

Alfa did indeed install a factory heat sheild over the exhaust manifold on the GTA corsa race cars. I am not sure if the Stradale versions had them, but I think that they did.

If it were me I would definitly Jet Hot the headers in white (a la Alfa Corse).
 

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Discussion Starter #16
Looks like Jet-Hot is the go. As to the downstream heat transfer, most of it will emanate from the mufflers due to gas expansion and as the underfloor insulation is still there and OK the cabin shouldn't get too hot, though if the floor does get warm it will be the passengers with the toasty feet as my car is RHD. When it gets back on the road again, just out of interest I'll take a few more temperature readings.
Regards to all,
Chris
 

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Well, as far as a thermal barrier coating for the header is concerned, the best solution is a zirconia coating by thermal spraying. The material is a zirconium oxide stabilized by approximately 8% yttrium oxide. The process you use is called plasma spraying. This produces a thin ceramic coating that is also used in aircraft turbines and stationary gas turbines. In comparison to other so-called ceramic coatings this is 100% ceramic. It is more expensive than other coatings, but it is state of the art. The color is egshell white and the surface is rough so it can be coated by any regular exhaust color. There should be a sufficient number of companies in the US that do this.
 

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Got some results.
My car doesn't move at the moment (no wheels) so these will possibly be 'worst case' numbers. I taped the probe to the bell housing of the front brake booster then started the engine, adjusted the idle up to 1200rpm and closed the bonnet. After 10 minutes or so the engine had reached its operating temperature according to the water temp gauge. After a further 15 minutes the probe temp read a fairly stable 63.5degC (that's just over 146degF for you old fashioned Americans) though it was still edging up very slowly. That is fairly hot - I took some photos which I've attached. Interestingly, the outside bonnet temperature was about 37degC probably because I have no under bonnet insulation. These figures would be lower when driving and when I refit my wheels, after I sort the brakes, I'll try to get some numbers on the move.
Ciao,
Chris
Here are some test results I had with temps under the hood:

I have a highly modified engine but I have the stock 2 pc. cast iron header.

I fried my MSD ignition box on a 95F day while driving on a country hwy so I installed a cold air intake and a cool tunnel to keep it from happening again. The cool tunnel temps don't apply to this thread but the temps outside of it does. Notice the outside temps have a big effect on under hood temps.

Outside temps………………………........90 F………………75 F

1. Stop and go city driving

Outside of cool tunnel …………..................205………………….127
Inside of cool tunnel .............................134…………………..94

2. Hwy driving

Outside of cool tunnel…………………….....….205...................127
Inside of cool tunnel………………………........114.....................75


I used a lazer heat gun to take the temps and shot the MSD ignition box, cam cover, brake master cylinder, power steering fluid tank and the fender wall .....all on the exhaust manifold side. I would take the temps with in a minute of stopping the car after a drive. I drove both in the city and on the hwy.

The exhaust mainfold temps were off the scale but within a couple of minutes of cooling fell to 450 plus degrees.

The first pic is with the MSD ignition box that fried the second pic shows the cool box that I built to keep the new control box cool. The new ignition control box (Autronic 500 CID) has an operation temp range of upto 190F. Never could find any operationial temp range of the MSD box that fried but I bet was similar.
 

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