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footwell insulation
have done all the searches, but need to know what material works best for insulating the footwells, floor and firewall against heat. Sound insulation would be superfelous (sp?) on these cars, so thats not a concern. I'm thinking stainless steel plates in the engine compartment, but what in the interior?
All suggestions appreciated.! |
I have a padding with silver paper on one side and the padding on the other. I glued this shiny side out all around the engine compartment and footwells. It does not look the prettiest, but,hey, its pretty cool in the cabin!!
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I used a combination of Dynaliner, and two sided aluminum foil backed insulation. The 1/2" Dynaliner I used on the floors on top of the insulation, and under the carpet. The foot box front and sides, I just used the insulation material, and carpeted over it.. All seams were covered in DEI Heat tape.
In addition to this, I added an aluminum "stand-off plate" at the front of the foot box directly behind the headers. Small sections of aluminum tubing were used as spacers, and it was attached with machine screws and lock nuts. I'm very happy with the results. Even on the hottest days of summer, my feet stay plenty cool. http://i103.photobucket.com/albums/m...y/IMG_2967.jpg |
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KoolMat Hi-Tech Heat Insulation http://www.clubcobra.com/forums/pict...d=8685&thumb=1 |
The best way to deflect heat is gold foil.
As used on the mclarens and kirkham billet car. The stuff ain't cheap, but... |
The best way is to stop the heat soak to begin with on the outside of the foot boxes.
Silcone sheets on the outside between the heat shield and footbox works wonders. Then you sound insulate and pad the interior as usual. |
Here's the stuff I used:
http://http://www.lowes.com/pd_28929...ductId=1081449 It's FrostKing insulation. Foil on one side and adhesive on the other. It's the stuff recommended in the ERA build manual and it worked great. Maybe it's belt and suspenders, but I also used jute pad between this stuff and my carpet. Nice and quite (except for the sidepipe noise you want to hear) and no heat issues coming into the cockpit. Matt |
The Stainless Steel plates that stand-off the fiberglass footwells are quite good by themselves. The air gap between the SS plate and the fiberglass is quite a good insulator since air is flowing thru this area when the car is moving. The plates should be Stainless Steel and not aluminum and polishing them increases their effectiveness.
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Thanks guys for all the leads & suggestions, that'll give me plenty of options !
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I used Lizardskin throughout my cabin. You spray it on in thin layers until it reaches the thickness of a credit card. Fantastic product, you can actually sand it down and spray paint it if you need to.
http://www.clubcobra.com/photopost/d...6MVC-006S1.JPG http://www.clubcobra.com/photopost/d...26DSCF0125.jpg http://www.clubcobra.com/photopost/d...0/P1000217.jpg |
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The aluminum cool down easier and they don't need to be very thick. All what a heat shield does is keep the heat directly from the surface. With an 0.5 inch gap and a 18ga alu shield we talking about 250f (1 inch from the header) before and ambient temp after 0.5 inches. What helps the most is to wrap the headers (150f one inch from header), in combination with the heat shields. That helps to lower the overall engine department temp. |
Conductive Heat Transfer through Aluminum with thickness 2 mm and temperature difference 200 C (382 F)
q / A = 250 (W/mK) 200 (C) / 2 10-3 (m) = 25000 (kW/m2) Conductive Heat Transfer through Stainless Steel with thickness 2 mm and temperature difference 200 C (382 F) q / A = 16 (W/mK) 200 (C) / 2 10-3 (m) = 1600 (kW/m2) The emissivity coefficient - ε - indicates the radiation of heat from a 'grey body' according the Stefan-Boltzmann Law, compared with the radiation of heat from a ideal 'black body' with the emissivity coefficient ε = 1. Stainless Steel, weathered emissivity coefficient = 0.85 Stainless Steel, polished emissivity coefficient = 0.075 Way to technical for me, and while I have not personally confirmed the above technical information , I did stay at a Holiday Inn last night........:confused: |
It is just amazing how the internet creates all kinds of engineers.
One click and you have the right answers and formulas... WRONG! I like to visit my last statement: "The aluminum cool down easier and they don't need to be very thick. All what a heat shield does is keep the heat directly from the surface." Ergo, alu heats up faster and the heat conductivity is higher. With other words, if there is any little airflow striking the alu the radiation will be lower, because of the rapid change of molecules (principle of heat sink). Both shields will heat up to the same temperature inside the engine compartment eventually (no airflow) - the alu just a little faster, but is cooled down and radiates less on the other side when exposed to airflow. As soon the fan kicks, in you have airflow. As I said before, there is no gain (SS) with higher cost, more weight and harder handling. Google tip: https://www.google.com/search?q=auto...w=1785&bih=913 |
I think the issue here is how you and I perceive the function of the heat shield as used in this case.
You stated: …’ alu heats up faster and the heat conductivity is higher…” And I totally agree with that statement, but then wouldn’t all that additional heat that is transferred so much more efficiently thru the aluminum plate once again be interacting with the footwalls’ fiberglass and ultimately with your feet? Especially during periods of low air flow behind the heat shield plate. I don’t think the idea here is to create a heatsink here with aluminum, the goal is to reflect or slow down the efficient transfer of heat from the headers to the footwell fiberglass And using a material that does not conduct heat as easily thru itself, like stainless steel, prevents the efficient transfer of heat back to the fiberglass on the footwell. We are not trying to extract heat from the headers or area around them and actually attempting to “cool” it. And you were also correct in saying the stainless steel is a higher cost, has more weight and harder handling then aluminum, but these facts are not relevant to the question of heat transfer are they. And regarding your opening statement… --------------------------! |
They may not even make this now but I used Thermotech on my Cobra. Easy to cut, bends as easily as a blanket and it will withstand up to 1500 degrees. I even had my transmission tunnel lined with it and worked great. It came in a roll and you just unroll it and either glue it in or use screws. I think it was about 1/4 inch thick with the shinny side out. I even replaced some of my aluminum heat reflectors with it as it lowered the temperature behind the shield more than the aluminum did.
Ron ;) |
I expect there is always some airflow within the air space, when using a foot box deflector plate, (regardless of material used), via convection, caused by the heat itself..Hot air rises, drawing in the cooler air from the bottom. This takes place regardless if your moving, or if your cooling fan is running. Granted, it might not be as rapid an air movement, but the hot air is not trapped.
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