Ceramic coat vs foil for heat reflection?

E

Alex

If you were building a mini-air box out of 0.1'' aluminum and you wanted it to reflect heat away, would you ceramic coat it (like you would headers), or would you use that silver foil?

I'm not certain what to do, as I've read the ceramic coat can reflect ~90% of heat away, but foil can only do 60-80% depending on the brand.
 
MikeP

Mike Pass

Supporter
You need to reject two types of heat. Radiated heat (both radiated and absorbed) can be cut down by using shiny surfaces such as metal sheet or foil which act as a mirror for the infra red radiation. Black, rough surfaces are good radiators and absorbers and shiny, smooth, light coloured surfaces are bad radiators and absorbers of radiated heat.
The other type of heat transfer is conduction. Unfortunately metals are very good heat conductors and therefore are useless for reducing conduction. Aluminium is actually a very good conductor of heat. You therefore need a layer which is excellent at peventing conduction. It turns out that air is a very poor conductor of heat unless the air is free to move in which case the heat is carried by the process of convection - ie hot air rises carrying the heat with it. So what you need is air which is trapped so it can't move. So any kind of foam or wadding with a lot of air in it does the job really well. It also helps of the material of the wadding is also a good insulator itself so glass wool works well.
So the ideal is a material containing lots of air and a reflective top surface. The foil reflects the heat to cut radiated heat and the padding cuts the conducted heat. The thicker the wadding the better.
Ceramic coating will help a little bit with radiated heat especially with a silvery, shiny surface. Ceramics are very good insulators of heat but the coating is very, very thin so not very effective for your purpose but great on exhausts where the temps are very very high and the ceramic also cuts corrosion of the hot metal.
Cheers
Mike
 
CANTDRIVE55

Doc Kaler

Mike,

Nice description!

Alex,

Gold foils have higher reflective properties than the silver foil (that's why you see a lot of it used in track cars....and aerospace industry). Koolmat has a variety of surface treatments that might work for you.
 
blueovalz

Terry Oxandale

Skinny Man
Interesting. In my case where I've got bodywork about 3" (76mm), my intent is to use a quality reflector on a sheet of some kind of substrate that is spaced away from the body (10-20mm). This shouldn't take much space, and if needed, I may use a forced draft through this gap as a last resort to protecting the composite and paint.
 
blueovalz

Terry Oxandale

Skinny Man
I use this type of phenolic material in building structures and wheels for my rotating spark gap (gets pretty hot!), and I get mine on Ebay. The local "plastics" dealer decided to only sell entire 4' x 8' sheets (no more cut-offs), and I couldn't afford that kind of investment. So I turned to Ebay, and there is about any sized piece you would need. It aint cheap though.
 
E

Alex

Maybe ya'll can give me some further suggestions for my setup then. As a note, I have no intention of making it out of plastic or any type of special aerospace material - special materials are when project costs end up going from $100 to $5000, lol.

I could possibly make it out of fiberglass since it doesn't conduct heat, but I'd be concerned about how close it is to heat sources.

Anyways, here's the setup :

Engine needs ~1000cfm. So I'm using an EV Pro carb blow-through hat (flows 1400cfm n/a)
(generic picture)

2vadpg7.jpg


Air filter is 4'' connical, 12'' long (flows 1204cfm)


I've tried multiple ideas, but the only way I can position is to by basically putting a 30* angle onto the carb hat, then run the filter diagonal along the intake manifold like this:

airbox1.jpg


I've built a partial air box - it covers the bottom of the filter and goes half-way up the sides (I can't make it too big otherwise I won't be able to fit a rear scoop back there).

What I'm also going to do is cut 2 3'' holes on the side of the airbox, then run flexible ducting from those holes to 45* pipes located on the roll bars, directly in the path of oncoming air entering the rear scoop

airbox2.jpg


This way I can slam cool air into and around the air filter.

The only "bad" thing about this idea is that basically the filter is located behind the engine, above the transaxle (which can get hot).

I'm hoping that by using reflective foil on the outside of the box it will bounce most of the heat back; that, plus having 2 3'' ductings running into it, will keep the air relatively cool.

So I guess 2 questions

1 - Do you guys see anything wrong with this?

2 - Any suggestions to improve on this idea, heh.
 
A

Seymour Snerd

Lifetime Supporter
EFNFAST said:
1 - Do you guys see anything wrong with this?

2 - Any suggestions to improve on this idea, heh.
Click to expand...


I don't see anything wrong with it. My intuition is that "hot" by transaxle standards is not hot enough to radiate a significant amount of heat to the airbox. Hold your hand a few inches to the side of a 200 degree object and see if you feel anything. I'd be more worried about convected heat and conducted heat (i.e. hot air, particularly from the exhaust system). As long as there is air motion within the engine compartment that's not much of an issue.

But, with the SLC's sophisticated aerodynamics, when the car is in motion is there any air motion in the engine room? If not, could you arrange for some? Maybe bleed off some of the scoop air to cool the carburetor and airbox? If you don't have some you're going to have vapor lock problems, etc., with the fuel and carburetor, although that is lessened if you have a bypass regulated round-trip fuel system; I don't remember. But even so you still don't want the carb and intake tract sitting in hot air.

And then of course there's idling and heat soak when there's no natural air movement. That's when the transaxle might become a problem paricularly for anything sitting above it. The only real solution to that is keep air and fuel moving at all times. Insulation helps, but it's really only a delaying tactic. If nothing moves, everything in the engine room eventually arrives at the same temperature whether insulated or not.

As for the airbox, here's what I'm using for general purpose insulation: Thermo-Tec 14110 - Thermo-Tec Cool-It Insulating Mats - Overview - SummitRacing.com. It insulates and reflects.

BTW if you wanted to be cute about radiated heat you could polish the aluminum.

Extending the cuteness further you could build an outer airbox 1/4" larger than the inner one, attach in a few places to the inner box with something non-conductive (eg plastic spacers and/or nylon fasteners) and now you've got a very well insulated air box. Now polish the outer box.

If you want to be a really cool dude seal the two boxes together and evacuate the internal space. Now you've got a thermos.

However the thermotec stuff is lighter and simpler than an extra airbox....
 
Last edited:
E

Alex

awatkins said:
But, with the SLC's sophisticated aerodynamics, when the car is in motion is there any air motion in the engine room? If not, could you arrange for some? Maybe bleed off some of the scoop air to cool the carburetor and airbox? If you don't have some you're going to have vapor lock problems, etc., with the fuel and carburetor, although that is lessened if you have a bypass regulated round-trip fuel system; I don't remember. But even so you still don't want the carb and intake tract sitting in hot air.
Click to expand...

For additional clarification, this is the rear setup:

carb1-1.jpg


Normally it's enclosed in a plastic window; I want to vent as much heat as possible (and suck in as much cool air as possible), so I'll have Fran make me a rear scoop kinda like this (KINDA ... but smaller, more contoured, and more visually appealing)

29651173.jpeg


Basically there will be ~2.5'' tall opening at the front of it, going across the entire window section.

At speed this will suck in a crap load of air.

However, in order to get even more air to my filter box, what I'm going to do it attach 2 3'' 45* elbows onto the roll cage, kinda like this

airbox2.jpg


Then run 2 3'' flexible ducting from those elbows directly to my partial air-box I'm making.

My hope is that while moving air will be sucked into the scoop to keep the whole engine bay cool; in addition, I'll be routing air directly to the air box as well, feeding teh filter with cool air.

The above + reflecting heat away from the filter, I'm hoping will do the trick?
 
A

Seymour Snerd

Lifetime Supporter
Then run 2 3'' flexible ducting from those elbows directly to my partial air-box I'm making.

My hope is that while moving air will be sucked into the scoop to keep the whole engine bay cool; in addition, I'll be routing air directly to the air box as well, feeding teh filter with cool air.

The above + reflecting heat away from the filter, I'm hoping will do the trick?
Click to expand...

Seems to me it will work fine.

You didn't ask for comments on the overall layout, but I'll throw one out anyway. It strikes me that the carburetor is sitting there right below the apparent output of the roof scoop. IIRC, you can't see out the rear window anyway, so why not put an air cleaner right on the carb and then feed it directly from the rear of the roof scoop? Air path short and direct, with no chance to be heated by anything. Also way fewer parts.

How do the EFI SLC's handle this? What was Fran's intent?

----later---

Ok looked at a few build threads. EFI sucks from the rear...and I see your conversations with K&N about turbulence.... I wonder if it's turbulent at the rear of that long thin scoop. It looks like Cam put his air cleaner where he could get air from the side scoop.
 
Last edited:
W

Bill Musarra

Not knowing much(read any) about the SLCs. What intrigued me was the discussion of air movement in the engine bay. In the GT40s, several of us have noticed the proximity of the fibergass bodies to heat sources(exhaust) and the resultant effects of said heat. Notice what happened to my rear deck lid from just a tune session by my engine builder. Engine temps never went that high(around 160), but exhaust temps did(glowing exhaust[stainless] above 2000 rpm).
IMAG0028-1.jpg


In order to negate these effects a two pronged approach was taken. The first was to build up layers of high tolerance heat shield material on the fiberglass. See Chucks and others build threads concerning the use of various heat shield materials. The second approach was done by myself and several others. We installed small 5" fans in the front of the engine bays and set them up to run by switch and/or thermostats. Mine are temporarily set on a switch only and the engine builder didn't know to turn them on.
P8190251.jpg


P8190249.jpg

As an additional measure several of us installed "off delay" timers(Waytek) that allow the fans to run from 1 to 10 minutes after shutdown. I selected 3 for my car. In my car the lower rear trailing arm lives in an open tunnel. This space was used for the air to be drawn from to cool the engine bay.
A second thought along these lines, one could create flow through ventilation with small turbo fans that vent from the cabin to the engine bay for creating the air flow needed to at least keep it moving through the engine bay. These may not be an answer to the problem, but maybe it will trigger some thoughts along the line.

Bill
 
E

Alex

awatkins said:
Seems to me it will work fine.

You didn't ask for comments on the overall layout, but I'll throw one out anyway. It strikes me that the carburetor is sitting there right below the apparent output of the roof scoop. IIRC, you can't see out the rear window anyway, so why not put an air cleaner right on the carb and then feed it directly from the rear of the roof scoop? Air path short and direct, with no chance to be heated by anything. Also way fewer parts.

How do the EFI SLC's handle this? What was Fran's intent?

----later---

Ok looked at a few build threads. EFI sucks from the rear...and I see your conversations with K&N about turbulence.... I wonder if it's turbulent at the rear of that long thin scoop. It looks like Cam put his air cleaner where he could get air from the side scoop.
Click to expand...

I think Fran made a mistake when he designed the rear - he set it up primarily for EFI and not carb! Bad Fran! :drunk:

EFI uses a FAST intake manifold which is VERY low profile (relatively speaking) and the throttle body is at the rear. So that isn't a problem. Here's an example

http://www.gt40s.com/forum/286890-post133.html

Believe me, I WISH I could draw air down into the carb, but here's the problem:

carb3-2.jpg


carb6.jpg


As you can see, the carb sits very high up and the rear clip is about 1/2'' away from the rear-most vent tube on the carb. There's no room to fit a 14x4 or 11x4 round filter in there. Absolutely none - believe me, I've been trying like you wouldn't believe.

Howard used a flat panel airbox like this

http://www.gt40s.com/forum/327380-post314.html

But I've had several people warn me away from that setup - air likes to come in from the sides if drawn that way, and coming top-down may introduce unwanted turbulence. Not to mention I'd need a 17x11 rectangular filter!

I've tried to draw air from the side scoops, but in my build it won't be possible - the tall deck and big heads are going to f me up, lol, and I phsyically can't get a 4'' pipe, be it solid or flexible, to my side scoops. Phsyically impossible for my setup. The ONLY place I can draw air from is the front portion of the window (i.e., where the opening of the scoop will be).

I initially tried to point my filters there (such that it would be a U bend into the carb), but gave up because they'd be smashed right up onto my valve covers pretty much. Not to mention having that U bend wouldn't be anywhere near optimal for air flow.

So I'm hoping that by drawing air into my semi-air box from the scoop opening it will be enough to combat any warm air.
 
E

Alex

wbmusarra said:
Not knowing much(read any) about the SLCs. What intrigued me was the discussion of air movement in the engine bay. In the GT40s, several of us have noticed the proximity of the fibergass bodies to heat sources(exhaust) and the resultant effects of said heat. Notice what happened to my rear deck lid from just a tune session by my engine builder. Engine temps never went that high(around 160), but exhaust temps did(glowing exhaust[stainless] above 2000 rpm).


In order to negate these effects a two pronged approach was taken. The first was to build up layers of high tolerance heat shield material on the fiberglass. See Chucks and others build threads concerning the use of various heat shield materials. The second approach was done by myself and several others. We installed small 5" fans in the front of the engine bays and set them up to run by switch and/or thermostats. Mine are temporarily set on a switch only and the engine builder didn't know to turn them on.



As an additional measure several of us installed "off delay" timers(Waytek) that allow the fans to run from 1 to 10 minutes after shutdown. I selected 3 for my car. In my car the lower rear trailing arm lives in an open tunnel. This space was used for the air to be drawn from to cool the engine bay.
A second thought along these lines, one could create flow through ventilation with small turbo fans that vent from the cabin to the engine bay for creating the air flow needed to at least keep it moving through the engine bay. These may not be an answer to the problem, but maybe it will trigger some thoughts along the line.

Bill
Click to expand...

This might be a dumb question, but what if I bought 2 5'' fans and mounted them on either side of my partial air box and just had then run 24/7 (whenever ignition is on)? Would that help to repeal heat away from the filter (e.g., header heat), or would it be a waste of effort?
 
A

Seymour Snerd

Lifetime Supporter
EFNFAST said:
This might be a dumb question, but what if I bought 2 5'' fans and mounted them on either side of my partial air box and just had then run 24/7 (whenever ignition is on)? Would that help to repeal heat away from the filter (e.g., header heat), or would it be a waste of effort?
Click to expand...

Not a dumb question... that would certainly be simple, but running them when parked to head off vapor lock is one of the major benefits, hence the timer. But if you're not worried about that, then it certainly doesn't hurt. But at that point I think you're getting a benefit only when the car is moving at very low speeds (at high speed whatever the fan is doing will be swamped). Of course with the airbox right over the transaxle it's somewhat in the line of fire from air coming off the headers when you're moving so it might backfire (so to speak) on you. That's why I like the idea of putting the airbox "ahead of" all the sources of heat (like Cam's arrangement). That way you basically can't lose and don't have to add any "accesories" to mitigate the effects of placement. But I understand your space constraints.

Of course the other thing you could do is just build it the way you were going to, get it running, and then determine empirically if you have a problem with some measurements. A gizmo I discovered recently that's cheap and incredibly useful for this kind of thing is a little battery-operated data logger:

Amazon.com: Lascar EL-USB-1 Temperature Logger: Home Improvement

You put in the location of interest, drive around for a while, and then plug it into a USB port and voila there is a graph of temperature over time over essentially any reasonable period of time (it takes 16K readings at whatever frequency you choose).

(BTW the voltage-measuring version is outrageously useful for tracking down intermittent electrical problems).

One other crazy idea is to solve the problem the way some GT40 Mk II's did: put a bulge in the rear window to give you some more room. That might be a logical extension of the scoop addition.
 
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E

Alex

awatkins said:
That's why I like the idea of putting the airbox "ahead of" all the sources of heat (like Cam's arrangement). That way you basically can't lose and don't have to add any "accesories" to mitigate the effects of placement. But I understand your space constraints.
Click to expand...

If I could I would but I can't so I shan't :D
 
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