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Kirkham Motorsports

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  • 1 Post By 133bus
  • 1 Post By eschaider

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  #1 (permalink)  
Old 08-15-2020, 01:22 AM
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Default Header to fibreglass clearance

Apologies if what I'm asking has been covered before... I have built my own headers out of mild steel and have had them ceramic coated. I have 15mm between the rear header pipe and the the fibreglass footwell. Is this enough clearance, and or will it cause problems? I could fabricate a 2mm thick aluminium or stainless steel shield panel that I would create an air gap of a few millimetres between the footwell if necessary. I would appreciate any feedback or suggestions.

Will
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Old 08-15-2020, 06:38 AM
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Seems pretty close. It will make that foot box really hot on your feet.

John
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Old 08-15-2020, 06:56 AM
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I think that heat wrap would be your friend in that situation...I assume your concerned about what the heat will do to your footbox...my rear left header is only about 13mm from my alumunium footbox (LHD)..I have wrap on the header and a thin sheet of stick-on heat reflecting foil on the outside of the box where my foot is up against it for the throttle...only time it gets hot is in stoplight traffic...also I have wrap on the headers where they exit the body for the side pipes..they is only about 13mm clearance and have no problems at all...steve
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Old 08-15-2020, 10:02 AM
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You are close enough that the radiant heat off the header tube will burn the fiberglass and whoever's foot is on the other side in the footwell.

My suggestion would be a 3mm aluminum plate for heat shielding purposes that stands off the foot well by 12mm or so to provide an air gap for cooling. Secure it with aluminum stand offs at all four corners. I would also wrap the header tubes in one of the many lava based fine mesh heat shielding fabrics that are commercially available for the job. You should try to keep the wrapped tubes 50mm or farther, if possible, away from the 3mm aluminum heat shield.

If you really wanted to get after the heating try to also provide some cooling air flow to the area with ducting that draws air from high pressure areas on the front of the car and exhausts it downward over the heat shield exiting under the car. Be sure to consider some sort of fiberglass protection in the cooling exit path or you will eventually burn that glass up also.


Ed
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Old 08-16-2020, 11:36 AM
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I wrapped my headers and added heat shield material to my footbox fronts and tunnel. The shield material is aluminized fiberglass and will withstand 400 deg direct contact... 1100 ambient if I recall. DEI, Thermo Tec, Cool It, etc... Easy, good looking upgrade
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Old 08-16-2020, 03:02 PM
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The aluminized fiberglass is a good occasional protective shield. However it brings two limitations that you want to be attentive to. One is softening and the other is the oven effect it has over time on the encapsulated fiberglas core as a result of repeated heatings.

Aluminum melts at 1215˚F and softens at 600˚F. The manufacturer of the aluminized fiberglass that suggests it is useable up to a temperature of 1100˚F is providing optimistic, highly suspect guidance at the very least.

More significantly fiberglas resin that is repeatedly heated to high temperature (well below 1100˚F will experience resin deterioration that effectively reduces the resin, that bonds the fiberglass fibers together, to a talcum powder like residue. The bonding it provided to the fiberglass was long since lost.

Another consideration is the cooling of the heat shield. Aluminum is a heat conductor not a heat shield. While aluminum in sufficient volume is an excellent heat conductor. fiberglass is not. That means the heat the aluminum is exposed to is transferred to the fiberglass where it gets trapped and not surprisingly cooks the bonding resin yet again.

For the very occasional shielding of heat, aluminized fiberglass can be an attractive alternative. For a regularly repeating exposure to 1000+˚F (exhaust gas temps) heat source you would be better served with a solid aluminum plate of at least 0.125" (3mm) that has some source of air flow passing over it to sink away the heat it has absorbed off the headers.

This is a link to a State side performance shop that sells the Lava Rock brand of heat shielding, click here => Winding Road Racing. If you do an internet search in your geographic area you will find local race shops that offer the same or similar products. When you embark on one of these sorts of missions supplier proximity can be a real advantage.

BTW there is an ever growing reservoir of credible providers offering a variety of heat shielding. Get the best one (from your evaluation) that is as geographically close to you as possible.


Ed
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Last edited by eschaider; 08-18-2020 at 02:04 AM.. Reason: Spelling & Grammar
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Old 08-21-2020, 02:19 PM
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Thank you everyone for your replies. I like the idea of the Lava Rock sheeting. They list 2 different thickness sheets on their website, but it's not clear what the differences in properties are. My guess is the thicker sheet will provide greater insulation. Does anyone have any experience with both?
Will
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