Floorboard <==> Exhaust Pipe clearance and its effect on radiant cockpit heat

[Mark E.]

What's the recommended, or at least minimum clearance between the fiberglass floorboard and exhaust pipes on a C3?

I'm asking because I have a severe radiant heat problem along the bottom of the console next to the inside edge of each seat bottom. Once the car is at operating temperature, the carpet gets too hot to touch in this area. This heat is radiating from the exhaust pipes which are between 1/4" and 1/2" away from the fiberglass along this same area. I'm specifically talking about the section of exhaust from behind the frame cross-member to the rear of the of the floorboard where the inside edge of the seats are near. Talk about seat warmers!

I'm hoping rerouting the pipes with more clearance will help. But how much clearance should there be? I found no reference in AIM.

Also, who has wrapped exhaust pipes to reduce radiant cockpit heat? Results?
I believe the original pipes were double-walled- maybe to reduce heat? Since this type of pipe is apparently no longer available (I've asked a few shops and the parts houses), I'm wondering if wrap might be the next best thing.

[Patrick H.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

It's the nature of the beast. While my 71 and 72 have it a lot more, even the 2008 C6 has this.
You just can't have a low slung car, run as much ground clearance as you need, and not have the heat get you.

You could try reflective insulation on the bottom of the bottom of the floor pan in an attempt to keep the heat out, as this would be better than wrapping the pipes. Dynamat also makes some products that would help.

[Terry M.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

The clearance of the exhaust pipes is given in your copy of the AIM (Assembly Instruction Manual). Those will be factory dimensions and apply to the factory, or OEM, exhaust system. Depending on who made your exhaust system it may be impossible to meet those dimensions.

[Douglas L.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

Purchased a exhaust from Gardner exhaust for my 68. Fit was amazingly good and don't seem to remember it being anywhere near that close to the body.

On a related note, does anyone have a picture of the cross section of the double wall exhaust used by the factory. I'd be interested to see how it was constructed.

Doug

[Mark E.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

The clearance of the exhaust pipes is given in your copy of the AIM.

Terry- Before posting this thread I researched the '70 AIM but didn't see anything. Did I miss it?

I would be appreciative if someone could tell me what the exhaust - floorboard clearance should be in this area.

My current exhaust works but it's very old and not original. If I learn that it's routed closer to the floor than it should be, that will inspire me to replace it.


Patrick- I'm in process of installing Dynamat and Dynaliner, but wondered if it would also help to wrap the pipes. Anyone have experience with how effective that is?

[Bob R.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

I recently got to look at the underside of Jack Panzica's 66 he is a frequent poster here. He installed 3" diameter flexible metal dryer hose over the regular exhaust pipes to reduce the heat. He told me the regular exhaust heats up to 500 degrees and the dryer hose over it only gets to 150 degrees. He drives his car a lot and said it made a big difference in the passenger compartment temperature.

[Patrick H.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

On a 72 I have worked on changing to full time vacuum advance made a huge difference in the amount of heat it made. It runs far cooler now than it did, even though all of the factory configuration pieces were working.

If your car is still set up for the part time TCS vacuum you might want to switch that and optimize the distributor curve.

[Terry M.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

[QUOTE=Mark Edmondson (22468);753464]Terry- Before posting this thread I researched the '70 AIM but didn't see anything. Did I miss it?

I would be appreciative if someone could tell me what the exhaust - floorboard clearance should be in this area.

My current exhaust works but it's very old and not original. If I learn that it's routed closer to the floor than it should be, that will inspire me to replace it.


Mark
There are half dozen clearances given on UPC8, Sheet A4.

[Bill L.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

Mark,

I am going to through this out there too.

If the rubber boot under the leather shifter boot is toast hot air will just pour in the cockpit. The rubber gets very brittle and on my 70 it was in bad shape and had broken open. NOS pieces are pretty plentiful if needed.


Bill

[Mark E.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

There are half dozen clearances given on UPC8, Sheet A4.

That explains why I missed it. My AIM has A1 - A5 but is missing A4 (should there also be pages beyond A5?). I guess it's one of those copy of a copy editions.

Does A4 show the floorboard to exhaust clearance for this area?

[Terry M.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

That explains why I missed it. My AIM has A1 - A5 but is missing A4 (should there also be pages beyond A5?). I guess it's one of those copy of a copy editions.

Does A4 show the floorboard to exhaust clearance for this area?

Mark

Mark,
I am aware of three different 1970 AIM books. I keep only one in the house. The others are in the garage library. The one I have has a lot of bleed-through on sheet A4 from sheet A3 on the reverse side. I will take it to work and scan it for you, and see if I can clean it up some to make it more readable. Send me an email (I don't accept PMs) with your email addy and I will send you the PDF of sheet A4.

To answer your question: the only front dimension it gives is to the cross member tube = .50 inch
If you have M40 the clearance to the transmission shift linkage is .75 to the shift bracket and .58 to the cable bellows.

Edit Add: It also shows clearance to LT-1 oil filter (Has to be the same as other small blocks) below filter .60 LT-1 to side of filter .62*, .50 LT-1. The * has a note at the bottom "* SETTING +/- .06"

[Mark E.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

Terry, Thank you for your generous offer; I appreciate it. From what you shared, sheet A4 doesn't have any specs for fiberglass <==> exhaust clearance... right? If so, then we don't really know how close to the fiberglass is too close... With only 1/4" I'm a bit worried about heat damage to the fiberglass, but wonder if that's just the way it is.

I believe some mid-years have shields clamped on the exhaust pipes. Those pipes must have significant floor board clearance for the shields.

[Terry M.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

Terry, Thank you for your generous offer; I appreciate it. From what you shared, sheet A4 doesn't have any specs for fiberglass <==> exhaust clearance... right? If so, then we don't really know how close to the fiberglass is too close... With only 1/4" I'm a bit worried about heat damage to the fiberglass, but wonder if that's just the way it is.

I believe some mid-years have shields clamped on the exhaust pipes. Those pipes must have significant floor board clearance for the shields.

Mark, the sheet A4 does give clearance to the body after the pipes pass through the center cross member. in the area where the pipes are flattened. The lowest number is .95-inch at 45 degrees on the RH pipe (1.0 @ 50 degrees). The LH pipe is 1.20 @45 degrees (1.45 @ 50 degrees). However other than the oil filter and the M40 linkage there is nothing for the header pipes.

Just a thought I saw in another post. The "oxbow bracket" at the rear transmission mount is different for 2-inch pipes vs 2.5-inch pipes. You do have the appropriate bracket for the size of pipes?

[Mark E.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

Thanks Terry. I'm not clear what ".95-inch at 45 degrees on the RH pipe (1.0 @ 50 degrees)" and "LH pipe is 1.20 @45 degrees (1.45 @ 50 degrees)" means. But I sent you an email so maybe I'll better understand when I see a diagram.

Also, you say "...after the pipes pass through the center cross member, in the area where the pipes are flattened." I know the pipes are flattened for ground clearance as they go below the differential, but didn't realize they are also flattened behind the center cross member, below where the seats are located. Is this correct?

The bracket behind the Muncie ("ox-bow bracket") appears to mate to the 2 1/2" pipes with a similar curvature. I guess it makes sense there's a different bracket for cars with 2" pipes.

[Terry M.]

Re: Floorboard &lt;==&gt; Exhaust Pipe clearance and its effect on radiant cockpit heat

Thanks Terry. I'm not clear what ".95-inch at 45 degrees on the RH pipe (1.0 @ 50 degrees)" and "LH pipe is 1.20 @45 degrees (1.45 @ 50 degrees)" means. But I sent you an email so maybe I'll better understand when I see a diagram.

Also, you say "...after the pipes pass through the center cross member, in the area where the pipes are flattened." I know the pipes are flattened for ground clearance as they go below the differential, but didn't realize they are also flattened behind the center cross member, below where the seats are located. Is this correct?

The bracket behind the Muncie ("ox-bow bracket") appears to mate to the 2 1/2" pipes with a similar curvature. I guess it makes sense there's a different bracket for cars with 2" pipes.

I think the number of degrees is referenced relative to an imaginary vertical line drawn through the center of the engine. The detail with those measurements shows a line labeled CL ( The L overlaps the C which is engineer speak for center line) ENGINE. This will be much clearer once you see the picture. It truly is a case of a picture is worth a thousand words. I would post the PDF here (if I could) but I doubt I could make it large enough for you to see these details.

All I can tell you is the drawing shows the pipes flattened much farther forward than they were in practice. The OEM 2-inch pipes are hardly flattened at all. I can't defend the drawing. It is what it is.

It even shows lines for gap at the exhaust tips, but no dimension is there. ZThe newest revision on it is 6-30-69. If anyone has A UPC 8 Sheet A4 with newer revisions I sure would appreciate a copy.

1970 AIM UPC8 Sheet A4.pdf

It looks like this might work after all.