Zircotec's thermal barrier coatings

[Guest]

Hello.

 

I would be interested if anybody has experience of using this type of coating or views as to why not.

 

This is a completely different process to exhaust manifold paint and fabric wrap. 

 

Obviously its main impact is controlling heat given off by the exhaust manifold, thus lowering the under bonnet temperature.

 

My thought (rightly or wrongly) is that heat has to be dissipated somewhere and if it's not coming off from the manifold what is absorbing that heat in its place, with possible negative effects.

 

Does the cylinder head absorb more of the manifold heat and if so is that likely to cause problems ??

 

Vehicle in question: Mk 2 Vitesse.

 

I'd appreciate your thoughts - negative and positive.

 

Thank you.

 

Richard.

[getsis]

It's rubbish, waste of money if you want to reduce heat under the bonnet, doesn't last too long either, only thing going for it it looks good.

Best wrap it if you want to reduce heat under the bonnet.

[Colin Lindsay]

 

 

My thought (rightly or wrongly) is that heat has to be dissipated somewhere and if it's not coming off from the manifold what is absorbing that heat in its place, with possible negative effects.

 

 

Good point. All the extra heat has to go somewhere and it will put more strain on your cooling system, so that needs to be top notch. Is your under bonnet heat really excessive, or causing problems? I’ve always found the best solution to be a good free flow of air, possibly with an uprated fan.

[Chris A]

Best solution: drive faster, more air through the engine bay  

[JohnD]

If an exhaust manifold and exhaust pipe were made of something that didn't conduct heat at all, then the heat would disappear down the exhaust pipe.

There would be no more strain on the engine cooing.

The difference would be that the exhaust gases would be a bit hotter as they leave.

 

I've asked before how a coating less than a millimeter thick can have a significant effect, when to combat a similar temperature difference, the Space Shuttle needed ceramic tiles at least six inches thick.

I've not had an answer that I can understand.

I can understand that in professional motorsport the small difference can be worthwhile.

 

John

[Guest]

The only reason I flagged this up was that I have just got back from doing some touring in Francs and on one of the days the outside temperature was 35 degrees. The car was okay but it did get a tad irritable as the under bonnet temp increased. 

 

The electric fan / cooling system did its job by keeping the needle away from the red - albeit the fan (120W) was running full time during stop start traffic which lasted about an hour.

 

The car (Vitesse Mk2) has a full size electric fan (12") and the cooling system is in excellent order having been recently overhauled when I replaced the head for an unleaded unit. 

 

I guess there comes a point when the outside temperature is too hot to have any REAL cooling effect on the rad as its pulled in by the fan - just my thought be it incorrect or not.

 

Hence I thought about alternative opportunities for under bonnet temperature.

 

The reality is that to encounter those sort of temperatures is few & far between; so perhaps it's a case of accepting the rarity of the situation when it arises.

 

Regards.

 

Richard.

[JohnD]

The worst this very hot day, compared to a freezing one, can do is reduce the temperature gradient between air and engine coolant by 35C.

Not a lot, but significant if your radiator isn't working well - did you change that when you did the other work on the engine?

Many original radiators are now getting a bit clagged up, and it shows when stressed in this way.

Modern repros are not durable - you might think about having a new matrix fitted to yours, if the tanks and hose connectors are in good nick.

 

Increasing under bonnet ventilation is the only way to get air circulating more, and that means more holes in the bonnet, which you may consider unacceptable.

Louvres can look good, but are non-functional at speed, esp. if fitted too far back (see GT6!) so that they work in the high pressure bubble in front of the windscreen, but they can let hot air out when stationary.

Best would be a extractor duct, not a NACA, in the the top panel, just behind the radiator. or else in the side panels.

I fitted these to Old Blue Vitesse, many years ago, see pic.

 

 

It extends well forward inside the panel, so that the vortex caused by the tripping lip at the front works against the back of the duct to energise the air there and draw it out.

It is effective!

 

John

[AidanT]

Hi 

 

From the above then - Is it better to keep or remove the engine valances to have a better flow of air and therefore a cooler engine? Is this why most cars don't have them any more?

 

Thx

[Colin Lindsay]

Engine valences cover the lower part of the block and don’t really make any difference to heat dissipation. Most modern cars have them still in the form of inner wings (more or less). Keep a good flow of air through your radiator and keep it moving i.e. as John says let it escape through properly sited ducts or else with electronic help e.g. an electric fan. The difference between properly functioning and overheating isn’t great so it only takes a good flow of air, not an arctic blast. A well-maintained system is more than adequate for even stationary traffic and remember a good heater will also remove a lot of the engine heat if necessary. Just keep the windows down!

[dougbgt6]

Don't agree with that. With the valences air flow is from the front, along the sides off the engine and down past the gear box. Without, the flow is not directed over the gear box. Valences are missing from a lot of cars because they are made of cardboard and fall to bits or some professor of thermodynamics thinks removal is an improvement.  My rule number one is, Triumph put it there for a reason, so keep it there!

[JohnD]

I think Triumph put them there because the wheel wells in the bonnet were seen as providing insufficient protection from road water and dirt.

 

You are correct about the hot air's exit path from the under-bonnet - see any of my posts about heat in the cockpit -  but that is a narrow and congested route.

JOhn

[Mjit]

I've asked before how a coating less than a millimeter thick can have a significant effect, when to combat a similar temperature difference, the Space Shuttle needed ceramic tiles at least six inches thick.

 

This comes down to 3 main factors - temperature range, application and safety.

 

Temperature Range

A ceramic exhaust coating applied to a steel exhaust manifold has to deal with a temperature range of what, 303k to 922k (-30C to 650C) between a cold morning and hot running in most parts of the world.  A Space Shuttle had to deal with a temperature range more like 30k to 1920K (-240C to 1650C) between being in the shadow of the earth and reentry.  That's a much bigger temerature range at which the material must remain stable and not crack or flake off of the  surface it's bonded too.

 

Application

With an exhaust manifold you have hot exhaust gasses, then a good thermal conductor (steel), then a reasonable conductor (air).  The thermal coating just has to keep the heat in the best conductor and prevent it going to a less-good conductor.  This is just 'encorraging' the heat to stay in the best conductor.

 

With the Space Shuttle you have the air molecules creating the heat via friction and a good conductor (aluminium Space Shuttle airframe).  The thermal layer's job here is to stop heat going the other way to the exhaust manifold, from less-good to better conductor.  If it fails the aluminium will quickly absorb heat to and past it's melting point.  This is trying to stop the heat transferring to the best conductor. 

 

Safety

What happens if the ceramic coating on an exhaust manifold isn't perfectly even and you have thick spots and thin spots?  What happens if  there's a missed but?  What happens if it gets chipped or starts flaking off?  In general you get some areas that are slightly hotter than others and a pissed off owner who's spent loads of money only for the coating to start falling off.

 

Unlike the exhaust coating the Space Shuttle tiles are critical to the safety of the craft and crew and tragically we've seen what happens when they fail.

[JohnD]

The Space Shuttle was made of aluminium alloy, that could not tolerate a temperature of more than 175C without weakening.

And not all the tiles on the Shuttle had to face as high a temperature as the leading edges, where the above would be true.  In places such as the upper wing surfaces tiles of the same material as on the lower surfaces protected from temperatures less than 650C, by being 1.4 inches thick, and in some areas as little as 0.2".  Or 5mm.

 

That is a temperature gradient of 475C, that needed ceramic insulation at least 300 times thicker than Zircotek exhaust coating.

 

JOhn

[Darren Groves]

Have I joined the NASA Forum by mistake, I wanted to read about Triumphs.....

[JohnD]

Then don't read this thread, Darren.

To "land a man on the Moon and return him safely to Earth" was a Triumph, and if you can't see that, then then you have no soul.

JOhn

[Darren Groves]

I was joking, lighten up....

[JohnD]

Joke? What joke?

 

John

[Guest]

Gents.

 

Being the originator of the thread, I'm grateful for everybody's input. 

 

Additionally I can see both sides of the thread - mainstream issue & other side issues !!

 

It's the mixture of pertinent points along with other "matters arising" that makes this forum so interesting and having the odd tangent of additional information thrown in makes very interesting reading IMHO. I'm certainly not adverse to reading additional snippets of information.

 

It's a happy ship, so I reckon "steady as she goes" on all bearings.

 

Best wishes.

 

Richard.

[Darren Groves]

The space shuttle's Thermal Protection System, or heat shield, contains more than 30,000 tiles that are constructed essentially of sand.

 

All of the tiles are thoroughly inspected before liftoff – they are a crucial tool that allows the space shuttle to endure the intense heat endured when the shuttle re-enters Earth's atmosphere to land. After the tiles are heated to peak temperature, the tiles can cool fast enough to be held in your hand only a minute later.

 

I can use Google as well 

[dougbgt6]

They have one of the moon capsules in the Science Museum in London. I don't remember tiles on it, the thing that struck me was how small it was.

[Freyasgrandad]

A number of years ago I tried on of these ceramic exhaust coatings on the manifold and collector of my Toyota F3 car. As this was a mid engine single seater under bonnet temperature was not the issue, but here is a summary of what the makers promotional material said:

 

"Traditional cast iron exhaust manifolds retain more exhaust heat than tubular steel versions and in this respect they are superior in terms of performance as the retained energy accelerates the exhaust gasses through the system improving inlet flow during valve overlap. However cast manifolds seldom provide the optimum flow and pulse matching of tubular versions. Coating your tubular manifold with (brand name I won't mention) will retain energy in the exhaust that would normally be lost as heat thus offering the advantages of a cast manifold to the superior design of a tubular one."

 

In practice I found it to be very difficult to satisfactorily apply according to the instructions and less than attractive when applied.

 

Did it work? All I will say is that I ended up with a chrome plated system (and no this doesn't retain the heat).

 

One thing my engine builder did confirm as true is that cast iron manifolds are better than tubular if they are properly designed. The example he used was the Dodge "Ram's Horns" as fitted to early Hemi engines that were still the holy grail of Pro Street drag racers years after they had gone out of production.

 

If under bonnet heat is your main concern then thermal wrap is the best solution currently available and therefore does also retain heat in the exhaust.