Exhaust Manifold Wrap: Good or Bad?

[Stu 1986]

Hello Chaps,
I've been suffering a bit with the fuel evaporation issue on my Vitesse engine. I understand the cause of this to be the heat from the manifold when the engine is switched off, and have seen some heat shields on eBay I was intending to buy in the near future.

However I was musing on the matter today and wondered if exhaust wrap would help reduce heat? Is the wrap good or will it make little or no difference?

Any input is very much appreciated.

S. 😎

[esxefi]

it does work but is not recommended to be fitted to stainless manifolds.apparently they fracture or can break up due to the high thermal cycling.

[Stu 1986]

I have the standard cast iron one, so hopefully I'll be ok if I decide to go in for it. Speaking to a biker friend today he said he was wary of the wrap because he'd heard that moisture develops inside the wrap and accelerates corrosion on the manifold.

Hmm...

[JohnD]

The inside of an exhaust manifold is about the same temperature as the outside of the Space Shuttle on re-entry.
That had to be protected, as it was mainly built of aluminium, which goes soft at that heat.
So it needed about 6 inches thickness of ceramic insulation to keep the airframe below that.

So, do you think that an eight of an inche of glass fibre wrap will do ANYTHING?

You are far better off with a heat shield, that absorbs the radiated heat and re-radiates it over a far lager area, so deflecting the heat from your carburettors.

John

[sx2visuvesi]

You could always do what Renault did on the later 5 GT Turbo.
Fit a cooling fan blow air onto the carburettor.

[Nick Jones]

Yes, some 80's Audis had similar - and they were injected - albeit mechanical K-jet.  My 90 had one.  Was to prevent the injectors vapour locking.

Nick

[RobPearce]

Quoted from JohnD

The inside of an exhaust manifold is about the same temperature as the outside of the Space Shuttle on re-entry.

No it isn't. Even on a seriously highly tuned engine running full whack on a dyno, where the exhaust can be made to glow cherry red, you're still a good couple of hundred degrees below the shuttle's re-entry temperature.

[JohnD]

Rob,
To be precise;
Exhaust gas temperature is from 800 to 1200C, depending on the A/F ratio, timing and the use of turbochargers. (Simon V, Oberholz G. and Meyer M.  "Exhaust gas temperature 1050C, An engineering challenge." Borg-Warner Turbo Systems Academy, Online at file: http://www.turbos.bwauto.com/tools/download.aspx?t=document&r=105&d=327 Accessed 15/5/16)

The HRSI tiles on the Shuttle were in areas that saw up to 1200C, and were 1 to 5 inches thick.    (Data from NASA)

And the temperature of cast iron glowing cherry red is about 900C.  http://www.hearth.com/talk/wiki/know-temperature-when-metal-glows-red/

OK, I overstated my case. FIVE inches, not six.  Sorry about that.   But I think my case stands, epsecilly about the greater effectivity of a heat shield over wrap.
John

[RobPearce]

Data from NASA that I've seen showed the peak surface temperature at 1650C - I looked into it when writing a science fiction story a few years back. To quote a NASA paper:

During re-entry, the Orbiter’s external surface reached extreme temperatures—up to 1,648°C (3,000°F).

So it seemed to me that you'd picked the highest possible (very unlikely) exhaust gas temperature and the lowest available estimate of the shuttle's temperature... and still only just made your claim.

[Jonny-Jimbo]

Also the shuttle had a surface temperature of (arguably) 1600C, roughly, but the exhaust GAS is around 800 to 1200C, depending on A/F ratio and turbos etc. If the GAS temperature is this, then the metal exhaust is going to be less than this, so the metal surface of the exhaust is not going to be  any higher.

However, John is right that a heat shield will be more effective.

[JohnD]

Read the articles I linked to.

Quibbling about the temperature doesn't change the argument.

JOhn  

[RobPearce]

I'm not disputing your choice of heat shield but your apparent reasoning was declared as being based on something that simply isn't true. And your linked articles are specifically NOT the figures I'm disputing. So please don't try to make out that I'm the one who's not read things. Make your arguments with true facts and they'll be much more convincing, regardless of whether your conclusions are right or wrong.

[Richard B]

The shuttle was a flawed design.  

If it had not been required for it to have the capability to do a right angle turn during descent (so that it could get to Edwards Air base for none NASA missions);

then the Delta wings would not have been required,
the descent time would have been halfed from 11 minutes to 5 minutes,
then the wings would have not gotton so hot,
and most likely the Columbia and Challenger losses would not have occured.

An amazing vehicle, but flawed.

I used exhaust wrap on my 6-3-1 as the PI throttle bodies were getting hot and seizing the brass spindles. I am considering ceramic plating on the manifold when the engine is re-installed.

[don cook1]

I was at Beaulieu on Saturday and was in the old bus shuttle, that was hot...about 70 deg!!

[Hogie]

Hi Richard,
                the wraping is rather tracor like and is a possible fire hazard - trapped oil/grease setting fire etc .
The ceramic is much easier on the eye but as it is so thin has a limited effect.

I have my TR4A ex-TRactor manifold ceramic coated - one layer inside and two outside. The pipes still look clean after 10 years use but as for reducing the engine bay heat - maybe a few degrees but nothing to get excited about.  

There was more wrong with the shuttle than its basic shape. Some of the subcontractors should be hung.

Roger

[JohnD]

But if you got sauna-naked on the bus you would have been arrested!
Nhoj

[Stu 1986]

Just to update, I've read some other stuff on the manifold wrap on other sites and sources and have decided against fitting it on my car. Four reasons for this:
1) It may begin to look scruffy sooner rather than later.
2) It appears to shorten the life significantly of exhaust components.
3) The heat shields look pretty nice, and I can put a slither of the heat reflective material I lined my gearbox tunnel with on the undersides for additional help.
4) I've fitted the piped to the air filter box and she doesn't seem to suffer as much as she did do.

Thanks for the help and sorry if I opened an can of worms! 🤔

[JohnD]

No worms, Stu, just 'vigorous debate'!
Glad you've chosen a shield - I'm sure you will find it effective.

JOhn

[MadMitch82]

no idea on cost (probably isn't cheap) but what of this:   http://www.zircotec.com/page/--performance-white/41
I have read about people using this in various magazines to reduce under bonnet temps, and being a coating, no corrosion issues.

[Jonny-Jimbo]

We used Zircotec white ceramic on our Formula Student car I used that on the exahust - I had to due to packaging constraints. We did a before and after test, and it reduced the ambient temperature of the exhaust space (between the engine block, carbon floor, fuel tank and seat back by around 50C depending on engine speeds and ambient temperature etc. We did also use heat shield between the zorst and the fuel tank, although the Zircotec did reduce the temp of the aluminium skin seat back to the point you could almost bear to put your hand on it...

However, we got the coating done for free as 'sponsorship' - would it be worth the few hundred quid it would have cost? Hard to say for anything other than a serious race application where you need all the help you can get...

[JohnD]

Excellent, Jonny!

I've not found any independent assessment of such ceramic coatings before, and I bow to your research that weakens my scepticism.
It IS effective, but as you say only reduced the ambient temp by 50C, and only  made the seat almost bearable to touch - not a great difference when, I submit m'lud, that  a shield would be more effective.

And cheaper!
John

[Clive]

A 50 degree drop sounds good to me! shows the stuff works well, though a before engine bay temp would help put it in perspective.

[Jonny-Jimbo]

Well, as I said, for us it worked and was free, which was a major constraint. The best insulator really is a reflective shield and an air gap. We used aluminium sandwich heat shield as well as the Zircotec between the exhaust and the fuel tank (only around 30mm at it's nearest point). Although I never took a reading of fuel temperature, we never suffered from any obvious signs of the fuel getting hot or boiling in the tank.

So, as I said, it DOES work, and in some cases a heat shield MAY not be possible to fit (possibly some regulations or rules about originality?). But due to the cost of the ceramic coating, I would say it's not a feasible option to reduce the engine bay heat in something like a mildly tuned Vitesse road car (to go back to Stu's predicament). Something like a tightly packaged Formula Car or similar, where you are into the realms of spending £100s of pounds to find fractions of a second, it's worth it, otherwise not.

From a longevity point of view, it lasted well in our application, although the car was only used in earnest for a shortish length of time, a few months in total running on the dyno, then in the car testing and then in competition. However, I used 0.9 and 1mm stainless steel for the exhaust (no budget for inconel   ) and where the headers came out of the head, they did glow bright red - by the time they got to the collector they had cooled a bit, and then at the collector it would glow occasionally, but mainly sit at a 'hot blue' colour. With the ceramic coating on the whole exhaust ran hotter and thus the gas velocity didn't drop as much, so we got better volumetric efficiency of the engine. Through the ceramic coating you could see the pipes still glowing red, and it did stay hotter further along the pipe.

So, there were minor power gains from using this too, but again, on anything but an all out race engine, it's use may not be valid.

Also, from a cosmetic point of view, being ceramic it is slightly porous, so the white colour stained easily, particularly with oily thumb prints etc - these may sand off easily, they may not, I never tried it. Also, the white turned to a dull yellow after a number of heat cycles, so if you were after a pristine engine bay, something other than white would be a good choice. I wanted blue to match our car, but they were doing a batch of white and it was free so I didn't complain.

[Hogie]

The Zircotec product isn't a couple of hundred - a lot lot more.
CamCoat costs less but is a slightly different product.

Before you applaud the 50'C you have to consider how big the engine bay is compared to what you want it for,
A small confined space may easily drop by many 'C. The typical TRiumph cathedral under the bonnet has a lot of volume and also another big heat source - the rad.

What I can say is that the Camcoat on my TR4A increased the exhaust temp at the end of the pipe quite a lot - it turned the bumper blue.
More heat out = less heat in the engine bay (but I wouldn;t say significant)

It does look good tho'
Roger  

[Jonny-Jimbo]

Quoted from cliftyhanger

A 50 degree drop sounds good to me! shows the stuff works well, though a before engine bay temp would help put it in perspective.

I'll see if I can dig out my old lap top and see if I can find it.

I know that the air space went from not being able to put your hand near the engine bay to being able to put your hand in for short spaces of time. Still very hot, but not horrendous.

To give you an idea of the packaging we were working with, this is a doodle of the cross section of the exhaust area. The exhausts came out of the engine, zig-zagged across the car into the collector, which then turned back on itself again for the secondary, and then back again to enter the 'silencer' (Ha, silencer, it was still 110dbA!) As you can see the seat back and fuel tank were very close to the exhaust, as I said, around 30mm or so...