‘74 DS Resto

No I am familiar with hot air rising. But if the pressure existing in the engine bay exceeds the ability of heated air to rise up past the sides of the engine "It ain't happening". Hence I suggested sourcing cooler air from somewhere further forward. As to the bonnet seal who knows, traditionally this area at the base of the windscreen was utilised to force air in. Scuttle venting, reverse bonnet scoops, cowl induction etc. Open the under dash vent in an old Valiant at 60mph (these are connected directly to the plenum at the base of the windscreen) and you'll soon be rid of any loose paper laying round on the floor. Perhaps when idling in Paris the seal's presence may be a hindrance but I think at speed the air flow in this area would actually be trying to push in. Whether it can or not would depend on the pressure present in the engine bay.
 

Buttercup

D Stracted
1000+ Posts
A Dee?
1st front?
2nd front?
3rd front?
BVH?
BVM?
BVA?
LHD?
RHD?
Carby?
IE?
Confort?
Pallas?
19?
20?
21?
23?
AC?
Not AC?
Glass roof?
Aluminium roof?
White?
Blue?
Beige?
Silver?
Yellow?

You know there is no such thing as a standard Dee.
 
A Dee?
1st front?
2nd front?
3rd front?
BVH?
BVM?
BVA?
LHD?
RHD?
Carby?
IE?
Confort?
Pallas?
19?
20?
21?
23?
AC?
Not AC?
Glass roof?
Aluminium roof?
White?
Blue?
Beige?
Silver?
Yellow?

You know there is no such thing as a standard Dee.
Sorry I thought we were discussing the before and after results of adding venting to a specific vehicle (not previously equipped with such) in a controlled environment. Anything else is just "I reckon".

The specifications of the starting vehicle is irrelevant, the only thing of importance is whether there is any measurable difference in the before and after data obtained.

Obviously (looking at your list) the test dummy can't be a black Safari with a steel roof?

Clearly if the initial data was sourced from a blue car, then vents were cut into a red one and the parameters rechecked, everything would be happening way faster on the red one.
 

DoubleChevron

Real cars have hydraulics
I just reread your latest post.
Is your idea of convection, just air trying to circulate only within the engine bay confines?
My idea of convection is cool air coming in from under the car or through the front apertures, then being heated by the various sources within the engine bay, then exitting through a high up aperture.
Obviously late cars with rear edge bonnet seals don't have an exit aperture high up.
So........ I'm suggesting we provide one.

At no time did I suggest that a convective flow within the closed space was going to contribute much.

The scuttle is the highest pressure area though ..... so where most manufactures have there cabin air intake. I wonder if they put that seal there to try and improve cooling at speed ..........
 

Buttercup

D Stracted
1000+ Posts
I'm sure Citroen's aerodynamics team approved of the cendrier location.

If I was going to add vents to my car......
(Hang on.... I have a '72 DS21iePallas, a perfectly standard car to conduct experiments on..... except it is green.
And I have several downgraded bonnets, and some downgraded front wings.....)
I would start with cendriers upgraded a little to suit the 3rd front.

Could I recover the costs from supplying kits?

I'll add it to the list of "important" jobs.
 
View attachment 133657View attachment 133657View attachment 133658View attachment 133659View attachment 133660

I found these images of the cendriers. It seems there was a significant internal panel difference in the wings. They would work very well with the more open wing construction of the later cars. Maybe they could be constructed from scratch using highly polished stainless steel or maybe chromed mild steel
I did see on the a French website that the early ones were aluminium (up to May 61) and the later ones were stainless steel They are apparently not directly interchangable as the respective guards have different part numbers. The aluminium ones certainly look more attractive having more depth and shape in the casting, as per attached photo. The stainless ones, (like in your photos) are a lot "flatter". They also came with block off plates stored on the sides of the guards (under the bonnet) that could be fitted to keep snow out; be pretty handy up here in QLD😉.
Rob.
 

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I'm sure Citroen's aerodynamics team approved of the cendrier location.

If I was going to add vents to my car......
(Hang on.... I have a '72 DS21iePallas, a perfectly standard car to conduct experiments on..... except it is green.
And I have several downgraded bonnets, and some downgraded front wings.....)
I would start with cendriers upgraded a little to suit the 3rd front.

Could I recover the costs from supplying kits?

I'll add it to the list of "important" jobs.
Green with a pink roof?
 
I'm sure Citroen's aerodynamics team approved of the cendrier location.

If I was going to add vents to my car......
(Hang on.... I have a '72 DS21iePallas, a perfectly standard car to conduct experiments on..... except it is green.
And I have several downgraded bonnets, and some downgraded front wings.....)
I would start with cendriers upgraded a little to suit the 3rd front.

Could I recover the costs from supplying kits?

I'll add it to the list of "important" jobs.
I did a little research and it's interesting to note that Citroen claimed that their "underhood" aerodynamic changes alone (for the 2nd nose restyle) were responsible for a 4 mph increase in top speed and a 4 mpg improvement in fuel consumption at high speed (over the 1st nose).
Also of interest (according to the French website that I got the photo of the cendrier off) was that the DSs with cendriers got a full length seal where the bonnet meets the guard wheras the ones without cendriers just had little segments of seal. It didn't explain why, but my guess is that air being pushed out of the gap under the bonnet's sides was meeting air coming out of the cendriers with undesirable effects.
My understanding is that cendriers were only fitted on the 1st nose cars, so Citroen's aforementioned claims of aerodynamic improvement on the 2nd nose must have come from guiding more air down underneath the car?
Based on this rationale the seal at the base of the screen on the 3rd nose, along with the full length guard seals on the 3rd nose are probably all there for the same reason (to make the under bonnet air flow down). Period Citroen rally cars don't seem to have any extra venting except for one photo I found of a car with gills in the guards behind the front wheels?
The purported reasoning for fitting the vents in the top of the guards was due to "extra heat from the DS's hydraulics"? The early cars also had about 3 foot of exhaust pipe making its way forward in the engine bay, so possibly a combination of both? Perhaps once they got rid of this heat source (the longer exhaust pipe) the need for cendriers became obsolete? They both seen to have disappeared at the same time?
No doubt some hot air would bleed out of any sort of upper engine bay venting at standstill, but what is happening at speed? They may need flaps to close them off once moving?
I don't think I'll be chopping any holes anywhere any time soon until someone else does it, with wind tunnel results ratifying some worthwhile improvements.
The aerodynamic team may have approved the cendriers in the first place but one would assume they also signed off on taking them away?
 

Buttercup

D Stracted
1000+ Posts
Yes, the 1st nose had 3 feet of exhaust going forward, but then it didn't have 3 feet of exhaust going down the side of the engine.

Lots of other things changed between 1st and 2nd fronts. The muffler location may have slightly changed the aerodynamics however it also changed the heat distribution under the car...... and probably not for the better. Similarly, the cabin air inlets may have reduced drag, but they also adversely affected cabin air flow.
I very much doubt the reality of the claimed aerodynamic improvements.
Some of the performance improvements will have come from engine improvements, and having driven both 1st and 2nd front Dees for hundreds of thousands of km, I don't think there is much difference in fuel economy.

I thought the whole basis of this discussion was a consideration of what options there were for reducing under bonnet temps and heat transfer to the cabin....... with particular attention to 3rd nose Dees.

I know from driving my DS21, it quickly heats up when sitting idling, but never has a cooling problem at good road speeds. To me the problem exists mostly at no or low speed, and small vents placed low in the front panels cannot contribute to air flow at such conditions.
My key point has been that vents high in the front wings, or at the rear corners of the bonnet would greatly help convective flow at no or low speed.
 
Yes, the 1st nose had 3 feet of exhaust going forward, but then it didn't have 3 feet of exhaust going down the side of the engine.

Lots of other things changed between 1st and 2nd fronts. The muffler location may have slightly changed the aerodynamics however it also changed the heat distribution under the car...... and probably not for the better. Similarly, the cabin air inlets may have reduced drag, but they also adversely affected cabin air flow.
I very much doubt the reality of the claimed aerodynamic improvements.
Some of the performance improvements will have come from engine improvements, and having driven both 1st and 2nd front Dees for hundreds of thousands of km, I don't think there is much difference in fuel economy.

I thought the whole basis of this discussion was a consideration of what options there were for reducing under bonnet temps and heat transfer to the cabin....... with particular attention to 3rd nose Dees.

I know from driving my DS21, it quickly heats up when sitting idling, but never has a cooling problem at good road speeds. To me the problem exists mostly at no or low speed, and small vents placed low in the front panels cannot contribute to air flow at such conditions.
My key point has been that vents high in the front wings, or at the rear corners of the bonnet would greatly help convective flow at no or low speed.
No argument on the likelihood that venting located high up in the engine bay would assist engine bay cooling to some degree (while stationary). The unknown is what will they do at speed? I think the difference in maximum speed between the 1st and 2nd nose is a matter of record; the mpg claim was at "high speed". This "high speed" wasn't quantified in the article, but being a factory figure was most likely an economy comparison based on lapping a test track for hours on end at maximum speed (not really daily driving conditions). Given that all the engine bay modifications after the 1st nose seem to be aimed at guiding heated air out the bottom of the the car it makes sense to also run the exhaust pipe straiģht down in the direction of flow.
I did read an article where Citroen designed the back of the car to replicate the aerodynamic benefits of a Kamm tail (obviously without the appearence of a Kamm tail). The extension of the roof over the back window provided the drop off and the short sharply curved boot lid allowed the air to keep falling to meet the rising airstream from the upwardly curved boot floor. Now I'm hypothesising here, but as one objective of a Kamm tail is to get the the underbody airstream to go up; would forcing as much hot air as possible under the car increase the speed at which the air rises out the back??? Citroen made the claimed improvements based on "engine compartment changes" but there was no specific details on exactly how they went about achieving it. One thing is for certain cendriers had no place in the new grand plan.
Plenty of major manufacturers have made an aerodynamic faux pas.
Many of the bonnet scoops in the "muscle car" era were found to be detrimental to cooling by causing the airflow through the radiator to stall, or by creating excess under bonnet turbulence.
The Lamborghini Countach's 0.42Cd figure speaks for itself.
The Porsche 917's legendary long tail?
One thing for sure all through the lifespan of the DS aerodynamics were really still in their infancy. A factory claimed Cd of 0.36 for the DS, (independent testing gave it a 0.38 Cd, at normal ride height).
Good for the day, but when you consider a Nissan Cube of all things has a 0.35 Cd???
Don't get me wrong, I think the cendriers look cool, but then so does a Countach.
 
I know from driving my DS21, it quickly heats up when sitting idling, but never has a cooling problem at good road speeds. To me the problem exists mostly at no or low speed, and small vents placed low in the front panels cannot contribute to air flow at such conditions.
My key point has been that vents high in the front wings, or at the rear corners of the bonnet would greatly help convective flow at no or low speed.
I wonder if this wagon is still around? Shannons auction 2011, the personalised NSW plate doesn't come up as active any more (CIT 23D). Cendriers and some extra bonnet vents on a 3rd nose. Someone somewhere already has some first hand insight into this!
 

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DoubleChevron

Real cars have hydraulics
I wonder if this wagon is still around? Shannons auction 2011, the personalised NSW plate doesn't come up as active any more (CIT 23D). Cendriers and some extra bonnet vents on a 3rd nose. Someone somewhere already has some first hand insight into this!

now that's interesting. I wonder if that is a low pressure area ... so will actually work (the panel is dropping away in that area)
 
now that's interesting. I wonder if that is a low pressure area ... so will actually work (the panel is dropping away in that area)
Yeah, I'm not sure.
Given that the source of flow is coming directly from the front, I think the air would still be travelling along the body lines at that point and there would actually be a boundary layer there? The low pressure at the base of the screen is created by the airflow's sudden upward change of direction.
But I'm no aerophysicist, so????
 

KAndy

New member
Wow, well that was an amazing conversation- thanks. I’ll be insulating the firewall and consider wrapping some of the exhaust tube but will not be drilling any ‘vents’ for now.
As I strip away bits to expose the engine I found I’m a fin and a bit down. Any suggestions for a fix, will it be fine as is, or even better has someone got a complete fan on the shelf somewhere just longing for a new home?

Keep well, Andy
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Hi Andy,

I reckon I would be trying to get another fan, I think think any attempts to repair would be of doubtful durability. Last thing you would need is a wayward blade damaging the radiator.

I have used exhaust wrap on many engines (cars and bikes) with no ill effects. However any research or opinions on this product fall into either the: it's sh#t or it's great category, no fence sitters on this one.😉

I have read to keep the firewall insulation thickness to a minimum, as there is not much of an air gap there as it is. Haven't tried it personally though.

Regards
Rob.
 
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KAndy

New member
All got a bit ugly today, cant believe it was actually running alright before I started on this
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Only option is to push on.
Got this far
 
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