Manifolds - Wrap or Ceramic anyone interested in a comparison?

[stephen cooper]

http://www.guy-croft.com/viewtopic.php?f=13&t=759&hilit=wrap

 

For me the heat has to go somewhere I am sceptical that it's good for the engine and suspect if wrap or coating was really that good more easy to follow results would be available.

 

Bare pipes and a heatshield for me

[RobH]

I'm betting that the wrap convects (have I got the correct term) way more heat away than a coated pipe, thus under bonnet air temps and probably the cockpit are going to be higher with wrap,

 

No i don't think so Alan. Surface area will work in exactly the opposite manner - with a greater surface area the heat transfers to a greater volume of air and hence the air temperature is lower for a given heat flux. The paper I linked to earlier (irrespective of its source) does give some figures for thermal conductivity which suggest the wrap might be a bit better than the ceramic - though obviously not as good as the 1/2 inch thickness they used for their tests. The Cam-Coat info is very interesting and does suggest that a reduction of radiated heat rather than convected heat is the main benefit from wrap or coating.

 

Incidentally the emissivity of most colour of paint is about the same as you can see from this table. Even white isn't much better:

https://thermometer.co.uk/img/documents/emissivity_table.pdf

The surface has to be shiny to really cut radiation, not just silver in colour - silver paint would probably be near to anodised aluminium.

Edited November 16, 2017 by RobH

[ed_h]

Yes, in general we need to be careful in relating color to emissivity. Emissivity is determined from a much broader bandwidth than that which determines color.

 

Surface sheen (flat vs gloss) is probably more important than visible color. A trick used professionally (I understand) is to use typists White-Out. It's easy to aply, easy to remove, and its emissivity is 0.96+.

 

Ed

[oldtuckunder]

I'm betting that the wrap convects (have I got the correct term) way more heat away than a coated pipe, thus under bonnet air temps and probably the cockpit are going to be higher with wrap,

 

No i don't think so Alan. Surface area will work in exactly the opposite manner - with a greater surface area the heat transfers to a greater volume of air and hence the air temperature is lower for a given heat flux.

 

Rob forgive me as I struggle to learn

 

But my logic was that say I have a very good heat source (like an exhaust pipe at 600C) and one pipe has a surface area of say 10sq in, and another has a surface area of 20sq in, if I put both in an identical air flow, and assuming that regardless of how much heat I take out of the surface (by convection) the supply side can supply more than I take out, would I not have a higher volume of air heated by the pipe with a larger surface area than I would by the smaller one?

 

Alan

[oldtuckunder]

 

Incidentally the emissivity of most colour of paint is about the same as you can see from this table. Even white isn't much better:

https://thermometer.co.uk/img/documents/emissivity_table.pdf

The surface has to be shiny to really cut radiation, not just silver in colour - silver paint would probably be near to anodised aluminium.

 

That could be why some of the coating companies do a Ceramic Finish that can be polished.

 

Does make one wonder if radiated heat is your problem, if polished Stainless Headers might be almost as good as Ceramic coated?

 

What's really interesting is that all the tests by coating manufactures always compare to bare metal headers, never wrapped, and also whilst saying which of their products and colour they tested, there is never any mention of what finish or colour the bare metal headers were.

 

Alan

[RobH]

 

Rob forgive me as I struggle to learn

 

But my logic was that say I have a very good heat source (like an exhaust pipe at 600C) and one pipe has a surface area of say 10sq in, and another has a surface area of 20sq in, if I put both in an identical air flow, and assuming that regardless of how much heat I take out of the surface (by convection) the supply side can supply more than I take out, would I not have a higher volume of air heated by the pipe with a larger surface area than I would by the smaller one?

 

Alan

Yes in that case Alan, but that is not the same as a wrapped pipe. With the larger pipe in your example the heat source is larger so both sources are providing the same output per unit area. If you wrap a small pipe then although the surface area gets bigger the source remains the same hence less flux per unit area at the outside surface.

[oldtuckunder]

But wrap isn't smooth, its all textured and has a lot more surface area than the smooth pipe its wrapped around.

 

Alan

[Peter Cobbold]

The Eng Toolbox table shows a huge rise in emssivity between polished and tarnished stainless steel.

So a wrap is going to radiate liike mad unless covered with a shiny surface.

I reckon the worst place for radiative heat transfer will be where the exh and intkae manifolds are really close... and difficult to wrap.

For an unfocussed source the intensity of radiation follows a square law: doubling the separation drops heat transfer 4 fold.

[oldtuckunder]

 

I reckon the worst place for radiative heat transfer will be where the exh and intkae manifolds are really close... and difficult to wrap.

 

 

Now that is an interesting one, and one I will measure tomorrow before "off with her head"

 

I have just squeezed one layer of wrap around the exhaust pipes next to the inlet manifold, however when we look at heat transfer at that point there is a lot coming into play. The flanges on the Exhaust and Inlet manifolds are butted together so there is a lot of conduction right at that point, the head is running at around 110C so some conduction there (but insignificant) and the manifold its self is heated so I would expect that it is up around the 85C mark anyway (or as I have explained to others) the inlet manifold is actually being cooled to keep it at 85C.

 

It will be interesting to see what the temperature difference is over the length of the tract.

 

I actually have a significant amount of shielding between the inlet manifold and the carbs, i.e keep the carbs cool, whilst the inlet manifold runs at designed temperature. As you have pointed out a few times Peter having the inlet manifold hot enough to prevent pooling and droplet formation on the walls is very important. I have my suspicions (i.e. I haven't calculated) that even with an inlet manifold at 85C the speed with which an induction charge goes through it that very little heat is transferred to the bulk of the air/fuel mixture.

 

Alan

 

One of the reasons I can think that someone like Vizard might polish an inlet manifold to reflect heat away, could be because they are using an uncooled manifold!

[RobH]

......The emissivity may increase by a linear amount between a bare and wrapped /coated pipe but the surface can only radiate at a rate determined by its surface temperature, so by reducing that temperature through coating you should reduce the radiated heat by the fourth power of the change. Which change dominates?

 

It does begin to look look as though baking foil over wrap is the best solution, but messy to achieve.

 

Alan - in the case of a wrapped pipe the surface area - the output area- increases but the input side has not because the pipe itself stays the same. The wrap should control the heat flux, so effectively you are sharing that flux over a larger area which ought to reduce the air temperature, compared to the same pipe if it had a smaller surface area with the same thermal resistance.

[oldtuckunder]

Thanks Rob, starting to understand now!

 

Now if I knew when Idling if it was radiated heat or convected heat that was the biggest problem I could start to decide which would be the best finish wrap or coating. I think when the car is running hard and moving I don't think it makes any difference (engine wise) which I use provided there is enough air flow through there and with the shielding I keep the Carbs and inlet air supply cool.

 

Maybe I might try a polished coating, as whilst it would be a pain I could always wrap afterwards if it proved not as good, and at least now I have wrap measurements to compare with. I just hate wasting money!

 

Alan

[Peter Cobbold]

Alan, yes heat transfer will be very little from wall to mixture at wot and higher rpm. Its the prolonged tickover condition that is the challenge. Its not only competitionTRs that can suffer,so sorting the wrapping etc will be useful to those stuck in traffic jams with a stuttering engine.

The water heating is only important for evaporating fuel in cold weather starting, otherwise its not doing much at all.

Peter

[oldtuckunder]

The water heating is only important for evaporating fuel in cold weather starting, otherwise its not doing much at all.

 

 

Think of it as water cooling and it takes on a different perspective

 

Alan

[Peter Cobbold]

 

Think of it as water cooling and it takes on a different perspective

 

Alan

But you're well on the way to killing heat transfer between manifolds then you can cut off the water hoses Peter

[MikeF]

 

Actually no. The difference is that on inlet there is not much helping it, at bes,,,,,,,,,s, there was a tuning tendency in the 60/70 to also increase exhaust valve size as well as inlet, but now it is realised that it achieves virtually nothing (enough is enough) and all it does is add weight into the valve train.

 

Alan

Sorry I wasn't clear, I was asking bout airflow into and out of the under bonnet area

[Hamish]

Alan

How about indirect forced air to the carbs / under bonnet for the event queue and start line

Something like this with a bit of ducting from the front to the carbs

https://www.demon-tweeks.co.uk/motorsport/driver-cooling/revotec-alloy-in-line-blower-fans

H

[Ben Freer]

Alan

How about indirect forced air to the carbs / under bonnet for the event queue and start line

Something like this with a bit of ducting from the front to the carbs

https://www.demon-tweeks.co.uk/motorsport/driver-cooling/revotec-alloy-in-line-blower-fans

H

I have installed something very similar in Geoffrey having had vaporisation issues in 30+ temperatures in June this year. Of course since them the temperature has gone down but I'm sure it has improved the lumpy/grumpy tickover in queues. The Revotec is one is expensive and I opted for a cheaper version from Merlin. It actually huffs more air than the Revotec version I mounted it in front of the radiator with ducting up to the carbs https://www.merlinmotorsport.co.uk/p/3-inch-76mm-diameter-in-line-blower-fan-cwp140

[Hamish]

Good find Ben

[RogerH]

Hi Ben,

just ordered that blower and some pipe to improve the demisting on the front screen.

 

Roger

[john.r.davies]

Kumar, NA., Kale, SP., Numerical simulation of steady state heat transfer in a ceramic-coated gas turbine blade International Journal of Heat and Mass Transfer Volume 45, Issue 24, November 2002, Pages 4831-4845

 

This is a theoretical, simulation study, of turbine blades, but it found that, "at 1500 K TET, radiation heat transfer rate from gas to an uncoated blade is 8.4% of total heat transfer rate which decreases to 3.4% in the presence of a TBC". (TBC= Thermal Barrier Coating)

But it concluded that, "In the presence of radiation and/or TBC the uncertainties in convection heat transfer coefficient do not have a significant effect on metal temperatures."

http://www.sciencedirect.com/science/article/pii/S0017931002001904

Edited December 2, 2017 by john.r.davies

[john.r.davies]

And also!

Re my ealrier comments, in this thread or another on the same subject, where I decsribed my headers flaking off great sheets of corrosion under fibre glass wrap.

This book concerns a whole SYMPOSIUM on " Corrosion of Metals Under Thermal Insulation: A Symposium Sponsored by ASTM Committees C-16 on Thermal Insulation ".

 

https://books.google.co.uk/books?id=FvAyB9tgazEC&pg=PA58&lpg=PA58&dq=Thermal++insulation+fibreglass+academic&source=bl&ots=scRgWyglyg&sig=di6dRYFD3Eph6b6e-yC5AacSEz0&hl=en&sa=X&ved=0ahUKEwiQgeXV-evXAhVBCMAKHWgIBRUQ6AEI3AIwCg#v=onepage&q=Thermal%20%20insulation%20fibreglass%20academic&f=false

 

It was in 1985, and included, "An Experimental Investigation of Stress Corrosion Cracking of Austenitic Stainless Steel under Insulation" (Gillette & Johnson, Fibreglass Ltd. Insulation Divison)

Their expriments showd that such corrosion did occur, although not with stainless, and was associated with Chlorine ions.

So, if you wrap, don't take the car out in winter!

 

John

Edited December 2, 2017 by john.r.davies

[oldtuckunder]

Hi Ben,

just ordered that blower and some pipe to improve the demisting on the front screen.

 

Roger

Isn't it going to look a bit ugly on top of the dash Roger?

 

Alan

[RogerH]

 

I have a cunning plan.

 

Roger

[oldtuckunder]

Re my ealrier comments, in this thread or another on the same subject, where I decsribed my headers flaking off great sheets of corrosion under fibre glass wrap.

 

So, if you wrap, don't take the car out in winter!

 

 

I certainly have a lot of that flakey stuff on the old mild steel wrapped ones, and the collector boxes blew themselves apart in a delaminating way halfway through the season.

 

The wrap does work, but if you warp mild steel and really get things hot! only plan on it lasting 4-5 years from my experience. PS and I don;t think my warp ever got wet.

 

Alan

[oldtuckunder]

Well I think I have made the decision to have a go at ceramic coating, its only money and I can always wrap it afterwards if as I suspect it may not be the best thing since sliced bread.

 

However making that decision has resulted in about 6 hours work this weekend. With a steel set of headers and wrap its dead easy fitting, do a trial fit, knock seven bells out it to get them to clear everything (space is a real premium on Vitesses & GT6's in that area) then wrap them, then fit them, and where they won't fit hit seven bells out of it again, easy.

 

Now I may be wrong but I suspect that Ceramic Coating may not like that technique! My assumption is that hit it with a hammer after being coated and it will flake or chip off, likewise rubbing against anything is also going to abrade the surface.

 

So for the first time I have taken a new set of stainless headers and diligently done all the bashing, squeezing, trial fit, mark up, bashing squeezing, trial fit, make a an extra long milling bit to get the flanges that jointly clamp header and inlet manifold the same thickness, trial fit, bashing etc. etc.

 

For the first time in my life I have a set of headers that just drop on, slide straight into the collector box, tighten up, don't foul anywhere, and don't touch each other.

 

If when their coated it doesn't work, I'll just have to adopt Roger's attitude and say "Hey but their Pretty" -- "Under that wrap"!

 

Just got to get a pair of wideband sensor bungs welded in, and they can go.

 

Alan