Heat Shield Spacing?

[Jacob]

I am planning to put heat shields in the front of each foot panel and those panels facing the engine...what is a good spacing distance? I am thinking 1/4" to 1/2"?
Suggestions?

[GoDadGo]

I split the difference and used 3/8" aluminum barrel spacers that use a #10 screw.
I purchased them through Amazon and they come in packs of 10.

[2bking]

Heat shields work by reflecting the radiant heat coming from the header tubes and other hot surfaces in the engine compartment. Since the headers have the highest surface temperature, most of the heat radiated in the engine compartment comes from them. A polished mirror like surface neither emits or receives heat through radiation so this principle applies to both the shields and headers. The higher reflectance (think mirror) of the shields, the more heat reflected away and the less heat absorbed into the shield material. Once absorbed the heat is dissipated through convection into the surrounding air, transmitted through the attachment points, and radiated back into the world. If the back sides of the shield is polished it will not radiate heat into the foot box. If the shield is thin and the attachment points have a very small contact area, very little heat can be transmitted in these locations leaving the heat absorbed to be convected away. Since the highest air flow across the shield will on the engine facing side, most of the heat will be removed by convection on the engine side. The air is mostly stagnant on the back side due to the small air gap so heat loss through convection is greatly reduced between the shield and foot box. A correctly working heat shield will have a surface temperature slightly higher than the surrounding air moving across the shield surface. The foot box temperature behind the heat shield will be approximately the same temperature as the shield.

This forms the argument for and against the shields. If the headers are polished or have a coating that reduces heat radiation, there is less heat to be reflected by the shields thus the shields may have a much less effect on the surface temperature of the foot box. If the headers are black and the outer foot box surfaces have a dull dark color, the heat shields will work very well. If the foot box has a polished surface, there is not much need for the shield. Now drive through a puddle of dirty water and all these brilliant techniques get muddied up.

Oh, the question was about spacing. I like GoDadGo answer.

[AC Bill]

Here's a picture of mine. It runs down the front of the foot box, and back under the front floor section to the cross-member in front of the seat.

[Gumball]

I went the opposite route and made my own heat shields for the headers....

http://i845.photobucket.com/albums/ab15/CCRsAC/IMG_20140609_2055158901_zps17c92ed8.jpg (http://s845.photobucket.com/user/CCRsAC/media/IMG_20140609_2055158901_zps17c92ed8.jpg.html)

[edwardb]

My response won't be nearly so technical as 2bking's. :) For three builds I've only ever used insulation on the inside of the footboxes. I've used Lizard Skin but there are many choices. That plus the carpet and I've never had any sense of heat radiating from the panels. That in 5+ seasons and thousands of miles. In all kinds of weather, including some blazing hot days.

To 2bking's point, builds were ceramic coated or SS headers. Several years ago, after a long cruise and engine operating at full temp for quite a while, stopped and immediately measured the footbox panels with an infrared thermometer. Almost everywhere the panels were only slightly warmer than ambient. In the immediate vicinity of the headers, they were a few degrees higher. But not enough to make any difference in how it felt on the inside. I personally don't think they're necessary.

I realize not everyone will agree with that. But it's my experience. I wonder if anyone has installed them after completing a build, or removed them after having them installed for some time, and felt any real difference.

[wallace18]

I also use lizard skin on the outside of the foot boxes with Eastwood thermcoustic panels on the inside under the carpet. Ceramic coated headers also. No heat problems at all inside the cockpit. JM2CW.

[Jeff Kleiner]

...I personally don't think they're necessary.

I realize not everyone will agree with that...

I do. Like edwardb I have insulation and carpet on the inside. Over nearly a decade I've been stuck on blazing hot days in interstate traffic snarls, slow moving city jam ups and sat in the grid line at the track. I've never felt that I was any hotter in the roadster (and it's black) than if I had been sitting in a lawn chair beside it.

Jeff

[Jacob McCrea]

This older thread touches on the original question toward the end. Apparently there is some consensus that a 1/4" air gap is plenty; I have no opinion on that point.

http://thefactoryfiveforum.com/showthread.php?20586-Type-65-heat-managment&highlight=material+heat+shields

Here is what I did on my Type 65, with shiny 24 gauge stainless sheet and 3/8" spacers:

62599

62600

62601

How well do they work? Who knows, I'm still working on it. But having no plans for A/C, carpet, sound deadening, etc., I figured I needed to do as much as possible to keep the heat out of the interior.

[phileas_fogg]

I installed heat shields because I like the look; if they happen to reduce heat a little then that's just a bonus. Shamelessly stealing the idea from MPTech, I used reverse mounted riv-nuts to mount them. The pictures below only show the shields on the front of the foot boxes. I test fit the engine to figure out where to mount the ones on the foot box sides.

https://farm5.staticflickr.com/4306/35456325964_786cfebe77_k.jpg (https://flic.kr/p/W29WqU)IMG_1708 (https://flic.kr/p/W29WqU) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

https://farm5.staticflickr.com/4302/35456248174_d1e9af293c_k.jpg (https://flic.kr/p/W29xiG)IMG_2139 (https://flic.kr/p/W29xiG) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

The shields are polished stainless steel from Online Metals (http://www.onlinemetals.com/merchant.cfm?id=735&step=2&top_cat=1&showunits=inches). I peeled the backing off front & back at final installation.


John