i've been thinking about your original post.
dredging my memory.
regarding in particular your thought on stick-on relflective heat shielding products on engine side of tin. (and with consideration of superhawk's comments further on in topic).

i once had the reasoning for the black paint explained to me by my old german mechanic back in the 80s when i asked him why the engine tin on the squareback was black.
i was a naive mid 20 year old thinking of hot aussie summers and light colors?

he corrected me.

he had started out as a VW mechanic and then trained as a factory porsche mechanic before coming to australia.
he explained the black paint is mostly for heat dissipation after shut down.

black absorbs on its hot side and radiates on the cold side with regard to the atmosphere and also heat sources nearby. this occurs regardless of atmosphere itself. as superhawk noted. radiation occurs in a vacuum. the lunar module used this principle on the moon to keep cool. you can read up on it. it had mostly reflective surfaces on its rear face pointed at the sun and it had patches of black in key positions where it pointed away from the sun. the black surfaces were radiators that lost heat to the cold vacuum of space in the shadows.

the way it works with a VW is the tin absorbs the heat from the hot cylinders and engine parts after shutdown on its rear face. its an efficient absorber as a dark colour. (it also conducts heat very well as its connected to the hot engine and its thin so it heats rapidly.
rather than re-radiate this back at the hot contained engine it loses the heat through radiation on the cold side which is the engine bay side. its enough of a difference that the engine can not continue to escalate in terms of heating after shut down.

to some extent it might do this while the engine is running but probably not of any significance as its the air volume moving through the engine that is doing the heavy lifting in the cooling department.

anyway, that is why VW used black engine tins. so did porsche when it came to 912s and 356s.

911s are another story. the fibreglass cooling ducting neither conducts nor has any radiating qualities. they must have done their maths and worked out it did not keep gaining temp for a short time after shutdown.

i remember i always let the engine on the suqareback idle for a few minutes after pulling in from the highway to allow it to cool down slightly on its own before i shut it down.
i used to do this on the advice of the same old german mechanic.

if that story was right about the engine tin it is perhaps not a good idea to use a reflective surface on the engine side of the tins as this would reflect the engines heat back at it. particularly after shutdown. but also perhaps during running.
i think the tins definitely are meant to absorb heat and then lose it by radiation into the engine bay. they are meant to pull heat away from the cylinders and heads that are the super hot items. i think that is why rocker covers are black etc.

it sounds anti intuitive but i believe that is the reasoning.

VW would have done their maths on this.
the same principle would affect a hi po type 4 engine producing more power.
it would be a situation where the darker tin is assisting to get rid of heat.
the volume of air being drawn into the engine bay counters any effects of radiation in the engine bay while the engine is actually running.

The firewall air deflectors create more “suction” under the car to help the fan blow air down.

Anyone know why the factory used two (2) under the car firewall deflectors instead of one longer piece across the bottom of the car at the bottom of the firewall?

When factories stared putting air deflectors/air dams under the front of cars to force more air into the radiator in front engined, water cooled cars, they used a long continuous piece of rubber/plastic below the bumper/radiator opening.

QUOTE(914sgofast2) good question.
QUOTE(r_towle @ Apr 2 2023, 05:04 PM)
Yes. (more “suction” under the car) My mistake was not considering the space between the deflectors.
So should have proposed a scoop forward of the fan that allows the deflectors to work as well.

the deflectors are more or less lined up with the rear exit openings in the underside tin (if you have the lower air guides) or more generally lined up with the air exit areas either side of crankcase.

radiators in front engine cars are centrally located and wide. hence the dam needs to be across most of the front.

i'm sure the vw/porsche engineers had the optimum solution when it came to those deflectors and real word tested it.

According to conventional mythology, VW & Porsche had no idea what type of oil should be used, what size the oil pump should be, or at what oil temperatures the engine should operate at.

@Superhawk996 i enjoyed reading your post @ #8.
it got me thinking again.
about 15 years ago i took part in a professional forum on insulation and energy efficiency in buildings. i thought maybe the most vivid way i could get some notions across was to discuss the first "dwelling" on another planet. the LMs.
i had to bone up on what NASA and Grumman got up to.
i found it fascinating.
incredible technical object then (and still now!) and i was only really concentrating on the insulation and heat control aspects of it. mostly they addressed the issue with knowing what to do with radiant energy.
i hadn't realised there were two basic material and color schemes for the LMs.
the first batch for the early missions which landed on the moon equator. as a laugh you could call those tropical spec lunar modules. the second batch for the missions which landed much further north of the equator. temperate zone LMs. quite noticeable differences in areas of black material versus reflective external shields.

not to mention the problem of thermal expansion at monstrous levels that no earthly object ever endured on the rear face which was oriented towards the sun. which didn't go down and didn't stop shining on them like a blowtorch.

i am pretty sure the black tin on a VW aircooled engine is a similar study in the use of an absorbing and radiating dark surface for heat control and heat loss. one thing you can bet on is that its black for a reason that has nothing to do with aesthetics or engine dressing. i'm guessing a black or dark side down towards the engine itself is the most important dark surface and should be black no matter what. i'm still thinking about the top surface but if NASA logic is correct well it ought to be black too. we get the extra benefit on earth as you point out of convection cooling as well. heating the air carries the heat away from the surface.

@wonkipop

You are correct.

Black is indeed the best color both for absorption and emission of radiant energy and why the OEM tin is black. Black on the inside to absorb as effectively as possible. Black on the outside to emit as effectively as possible. All about letting the radiant energy pass in & out as easily as possible to get it away from the engine. Likewise, you’ll notice any of the thermal dispersant coatings are black.

Having said that, I still had one set of my tin powder coated in red - cause’ ya’ know, it adds 10hp right?

Ideally, I would have had it masked so that it was black inside, red outside. But that probably also tips my hand about how worried I am about radiant cooling contribution on an otherwise stock engine.

incorrect. at least 20 hp.

i think red is sort up there heading towards black anyways.
or purple. going with the 70s.
white or silver would be kind of not what to do.

yeah. i figure the radiant performance is more to do with cool down after running.
and its kind of negated a bit by that magnesium fan casting that just sucks up everything from the crankcase etc via conduction and turns itself into a mini nuclear reactor for 20-30 minutes after shutdown. boiling your fuel lines. that was always porsches problem with the vapor lock syndrome. the mag fan shroud. the conventional VW type 4s didn't really have that problem since the fan shroud casting was hanging out the arse and having a whose hotter contest with the muffler. but at least all the heat could sort of get away. they were really testing things going mid engined. but it kind of worked ok really. certainly a lot better than most italian super cars of the same time - at least in a joint like australia.

Only one NOTE on Black used on 914 for radiant cooling

911S 2,4 1972 engine was painted in RED
911T 2.2 1972 engine was painted in GREEN
Was one simple immediate eye distinction System??
I don't remember if the interior color was different
https://photos.app.goo.gl/LC5eWJzzKMfDSVmq5
https://photos.app.goo.gl/veb7yo2yVwMd8y4z9

My opinion for the TWO deflector underside is that Porrshe prefers to have the Air free for cooling the central OIL CUP

@searunner

yeah the 911 "tin" ware is a whole other ballgame (as i conceded in an earlier post).

they are fibreglass anyway. non conductive.
and the engines are dry sumped and kind of super oil cooled.
+ the fan is massive.

there is other scientific stuff going down with the old 911 engine.
but interestingly its an upright fan blowing air down over the cylinders, kind of like the original beetle.

whereas the type 4 motor (leaving aside it being dropped into a 914) is actually designed to be a compact flat package. the old "suitcase" engine or as i think americans labeled it the "pancake motor". its real parameters are to to with its application in VW sedans and station wagons. and i'm sure metal for ducting was more economical than fibreglass which back in the 60s and 70s would have been exotic.

i'll just add that the space shuttle had black tiles on the bottom of it, which was the bit that got hottest during its missions. not silver and not white. also had various little areas of black tile dotted around its upper surfaces.

and the blackbird SR-71s that flew over russia on spy missions at fairly high speed back in the 60s and 70s were black despite the intense friction on their external surfaces.

its interesting stuff. heat and how to get rid of it.

@searunner

to expand naively on the space shuttle for instance.
and when i say expand, i mean very tentatively, because i ain't no NASA engineer.
but.

you are re-entering the atmosphere.
and you got heated plasma (ie air turning into something else very hot) below the surface of your vehicle, the last thing you want to do is reflect that heat and add to the temp of the plasma........
so you absorb it with black stuff.
thats thick enough to suck it up.
the fabulous tiles. like space age pottery.
they suck the heat up and don't conduct it to the aluminium structure they protect.
which would soften, melt and lead to destruction of the vehicle.

then as the spacecraft slows to less than about 7 times the speed of sound and gets into the lower atmosphere the said tiles can begin to radiate the heat out to the cooler air.
no plasma anymore ( super heated air ). and the equation reverses.

so long as you don't loose any tiles!

i think that is how it worked on the space shuttle in terms of black surfaces.

with a VW engine i think it works by the black tin absorbing engine heat because its being radiated at by the engine, but on the opposite surface the air is cooler so it radiates towards the cooler body, the air and looses the same heat that its absorbing on the other side. in effect it forms a pathway for the enclosed engine to lose some heat out to the surrouding air and also to not reflect the engines heat back at itself, but rather to draw some of that heat away from the engine in the radiant spectrum.

the fibreglass on the 911 engine cooling shrouding probably does a sort of similar job because it does not reflect heat back at the enclosed engine. however it would also not form a pathway for getting the heat out. maybe they didn't need a pathway out for the heat they just worked out they needed a non reflective and non conductive surface.

?

i don't really know. just stabbing a guess at the basics.

Good additional thought. Thanks

The 2 deflector design works very well. You have 4 vortices aligned with the cylinder areas that are creating a low-pressure area immediately behind them. The are not a scoop in a traditional sense. The do cause the air in the engine compartment to be pulled down and carried off. Increasing the efficiency of cooling. Think of the fan pushing air, and the low-pressure area sucking it.
This is one of the reasons we added "winglets" to the design. Keeping the air from rolling immediately over the edge and helping to increase the low pressure. It a 3% increase in efficiency. Not much, but if we are going to create something why just copy it??

Come on Mark...ya just looked over the port side of your airship on the end of the wing and thought it was a good idea!

Interesting how did you test for the 3% ?

this is getting good.
if @Mikey914 is serious thats probably how you do it.....in terms of attempting to tweak some extra cooling efficiency for all you dudes who insist on hotting up the type 4.

get that air to move through.
and assist the fan to move extra volume.

i dunno what the maths is, but if you get it accurately calculated its probably where the extra cooling can be found.

To be clear that's a 3% increase in the efficiency of the airfoil. Not the cooling capacity. Yes, a drop in the bucket, but a +.