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  #31  
Old 01-13-2011, 11:23 AM
bobadame bobadame is offline
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If you connect the shield to the heat source you will be creating a direct path for the heat to conduct directly into the shield. It would better for the shield to not touch the exhaust system. Attach it to the under body instead. This is still a conduction path but it will be conducting from a lower temperature source.

Stainless steel does conduct heat much slower than aluminum but it also looses heat much slower. If you direct fresh air into the space between the body and the heat shield through a couple of NACA ducts, the aluminum will dissipate heat into the air stream and be carried away much quicker than if it were made from stainless. This is why radiators are made from aluminum instead of stainless steel.

Last edited by bobadame; 01-13-2011 at 11:38 AM.
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  #32  
Old 01-13-2011, 12:59 PM
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Bob: The heat shield attached to the heat source is not my brainstorming idea. It has been used in the automotive industry for decades. The turbo on my diesel pickup has a stainless heat shield attached to the turbine housing with three bolts. I believe that the up pipes also have heat shields. I have a couple of Maserati turbos that have a full wrap on the exhaust pipe. They only touch the pipes at the ends at the attachment points. Heat shields attached to pipe is very common on motorcycle exhausts. It is not a new concept. It must work. Why would they go to the trouble and expense to use them if they were ineffective? They are not meant to be cool to the touch but to intercept the radiant energy and drop it to an acceptable level. I am pretty sure that I have seen some heat shields on my V12 Jaguar exhausts as well.
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Last edited by mr.c; 01-13-2011 at 01:02 PM.
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  #33  
Old 01-13-2011, 01:05 PM
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Corvettes also had the heat shields attached to the pipes.
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  #34  
Old 01-13-2011, 01:23 PM
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I just went out and looked under all of the vehicles in my yard. Every one of them has a heat shield attached to the exhaust to protect a component. Even my old 89 Ford van has a heat shield welded to the catalytic convertor to shield the transmission. The crown vic has shields, the Jag has shields, My turbo diesel pickup has shields. Well, I lied ,the forklift didn't have shields but the Kubota tractor did. Bolted right to the muffler.
Exhaust systems put out an amazing amount of radiant heat. Back in my early days of racing, I had a Stuska engine dyno. I didn't have a dedicated cell to run it so I was pretty close to the engine when I ran it up outside. I was probably holding the throttle open by hand. Yeah, I know, stupid idea. I was young and crazy. I am still one of the two. The radiant heat coming off of the side of those headers at 8500 rpm would probably cook a hot dog two feet or more away.
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Last edited by mr.c; 01-13-2011 at 01:28 PM.
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  #35  
Old 01-13-2011, 01:33 PM
bobadame bobadame is offline
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I'm not saying it doesn't work. I'm saying it could work better. In some of the examples you mention there really isn't a better option because of space or packaging limitations. Heat travels 3 ways, by conduction through a solid, by convection through a fluid (including air) and by radiation. When you weld something then reach down and pick it up, that's conduction through a solid, your hand. If you hold your hand over the hot metal, that's a combination of convection and radiation and it hurts less because you are not in direct contact. If you go outside on a sunny day and direct the sunlight at your face with a tilted mirror, you're feeling radiated heat. All I'm suggesting is that it is better to use the principals of physics to your advantage than to ignore them.

Last edited by bobadame; 01-13-2011 at 01:37 PM.
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  #36  
Old 01-13-2011, 02:42 PM
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OK. Bob wrote:"All I'm suggesting is that it is better to use the principals of physics to your advantage than to ignore them. "
Ignore them?
You are saying that attaching the heat shield to the firewall/panel is better. Here goes the physics thing. Now the heat shield (which is hot) is now attached to the panel that you are trying to protect. Enter the conduction thing you mentioned. Heat travels from shield through conduction into the firewall/footbox.
I am pretty sure that the auto industry has some engineers that are familiar with the laws of physics. They are laws after all. Metal conducts heat better than air. Best not coonect the heat to something you want cool. Air is a fairly decent heat barrier in itself. Much better than metal. Physics thing again.
Did you ever look at a stainless steel vacuum bottle? Now how does that work? It is one piece of stainless steel with the air evacuated from inside the chamber. It works because stainless steel is a very poor conductor of heat. The vacuum won't allow heat transfer through air from interior to exterior wall so the temperature variable must travel through the metal from the inside to the outside. It doesn't do that efficiently so you have a decent thermos that won't break if you drop it.
That is the end of my discussion on heat shields. Joel can/will decide the best approach for his situation. He appears to be a very capable individual. I am impressed with what I have seen of his project. Nice work Joel!
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  #37  
Old 01-13-2011, 02:56 PM
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I'm done too Cary. No point in warping this thread into an argument between a couple of stubborn old farts.

Almost done. You connect the aluminum fin to the body with something that doesn't transfer heat well, stainless steel stand offs.

Last edited by bobadame; 01-13-2011 at 03:00 PM.
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  #38  
Old 01-13-2011, 04:19 PM
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Thanks for the spirited discussion on the topic. I'm learning lot's of good stuff.

A suggestion that's part of the solution is to get a fresh air supply/flow to the tunnel area to carry away heat that does escape the pipes. I think I'm in luck here with a fresh air scoop and location that's fairly unique to the Ferrari GTO. Here's a couple of GTO pictures from my archives.





These are located at the back corners of the hood/bonnet. On the original GTO they have ducting under the hood directing the air into the cars interior. I'm guessing they were required because the cars interior became hot (thus driver uncomfortable) due to the same heat control issue under discussion. I'm guessing they have screens on them so that bugs (bees/hornets would be the worst) aren't rocketed into the interior only to be shot at the occupants.

I won't need them for interior air as I'm equipping the C5 GTO with air conditioning. On my car I can build some duct work that would direct the fresh air down the tunnel and across whatever heat shielding I can put in place. I will likely not put screens under the scoops as screens might reduce airflow.

On the subject of heat shielding, I'm guessing I won't have much choice of where to locate it and how to hang it. There just isn't much room in the tunnel given it has a 6 inch torque tube, shifter and linkage, 2 decent sized mufflers, and 2.5 inch exhaust pipes all located in it. My take away from the earlier posts is that the heat shielding should be made from stainless as long as it has an air gap between it and the aluminum. It sounds like my best bet would be to hang the shielding on the torque tube (I think they might have done this on the C5 Corvette) if I can.

I hadn't planned on this before but now I'm thinking I should put heat shielding between the exhaust pipes and the transaxle. I do know that heat is the enemy of gearboxes.
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  #39  
Old 01-13-2011, 05:29 PM
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There was an article quite a few years ago about a Ferrari GTO reunion. It was in Italy or France. The reunion was to be a low key rally type event where they would stop for meals at predetermined restaurants for the wine and cheese thing that is so popular with this set. The cars were shipped to the event from all over the planet. The particpants showed up decked out for the high life. Their female companions were in their finest social wear and fresh from the hair salons. It didn't take them long to figure out that a Ferrari GTO was intended to be raced and not for luxurious touring. They showed up to dine soaked in sweat with ruined hairdo's and smelling of motor oil and racing gasoline and their ears ringing. It didn't really set the mood that they had anticipated. They were all at each other's throats and the female companions departed to leave the boys to their toys. Many of the boys bailed out early as well. All in all it was a very humorous account of unrealized joy.
By the way,I have seen that #22 car at the Cavalino Classic in West Palm Beach. Ferrari of Washington sends down a couple of transporters for the January event. I probably have some track photos.
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  #40  
Old 01-13-2011, 07:47 PM
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Actually a 250GTO is a very civilized car and isn't that uncomfortable ala heat or seating position. And if used on the street the sound is easily tolerable. I worked years ago with many customers who still own '62 and '63 (rebodied '62) iterations of the GTO. Very familiar with them. For racetrack use, hearing protection is definitely recommended.

I've also known people in the past who have used them regularly for street transportation on an irregular or regular basis. (some added interiors to dampen the sound) The reputation they have is truly well deserved -- it is probably the best dual-usage racecar/streetcar of the era. (Jaguar Lightweights aren't fun and Cobra Daytona coupe's are cramped/hot/loud even on the street and nothing else is worth comparison)

Per the France event? It wasn't as bad due to temperatures as some have reported. The only negative of the event was an older gentleman pulling out directly in front of a customers all original '62 GTO which destroyed the front of the car. (rebuilt and probably better than new now)

Remember at the Pebble Beach concours d'elegance this upcoming August 2011 is a "Special Exhibition Class" solely for the Ferrari 250GTO's. I know of eleven cars already scheduled to attend and to be played with at the track the days before and on the road as well. These cars are driven and if you look closely, most of them have regular license plates on them for street use even today.
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