T4 Engine tin: thermal design Options

[914werke]

So seeing a product recently got me thinking about the result of its application & my own observations of how well (or not) the T4 handles air flow, Engine block cooling & resulting oil temperatures. (IMG:style_emoticons/default/smile.gif)

Its somewhat well known that ...in the 914.. the T4 suffers from less than optimal cooling from the front mounted impeller/fan particularly to the #3 Cylinder
& that it is vitally important to seal the tins multiple openings to contain as much laminar air flow front to back over the finned cylinders.
In a gross approach, the goal was to seal the engine compartment "intake" air on top from the eng. heated "cooling" air below the tins.
When a motor is new and all its components serviced & refreshed, the design does, or did, a pretty good job.
After years of use (neglect), elements (oil dirt mice ext) conspire to restrict that air flow.
As well as eng. heat causing hardening of rubber pieces that are intended to help contain that cooling air below.
Now almost 50 yrs on I see fewer & fewer "STOCK" engine configurations which you can guess usually means more heat to deal with.
Jake addressed the cooling air via his(?) DTM solution, but IMO its not very practical for stock or near stock motors (& expensive)

The go-to response to eliminate that heat is usually an additional or a remote oil cooler which comes with its own set of challenges. (IMG:style_emoticons/default/confused24.gif)
How about KISS (IMG:style_emoticons/default/biggrin.gif) Has anyone used any of the Fiberglass based stick-on reflective heat shielding products on the engine-sides of the tin?
Idea being rather than allow heat absorption to all the those steel pieces reflect it back to carried away by the cooling air?

BTW Im not a Porsche engineer...but I did stay in a Holiday Inn last night (IMG:style_emoticons/default/happy11.gif)

[wonkipop]

So seeing a product recently got me thinking about the result of its application & my own observations of how well (or not) the T4 handles air flow, Engine block cooling & resulting oil temperatures. (IMG:style_emoticons/default/smile.gif)

Its somewhat well known that ...in the 914.. the T4 suffers from less than optimal cooling from the front mounted impeller/fan particularly to the #3 Cylinder
& that it is vitally important to seal the tins multiple openings to contain as much laminar air flow front to back over the finned cylinders.
In a gross approach, the goal was to seal the engine compartment "intake" air on top from the eng. heated "cooling" air below the tins.
When a motor is new and all its components serviced & refreshed, the design does, or did, a pretty good job.
After years of use (neglect), elements (oil dirt mice ext) conspire to restrict that air flow.
As well as eng. heat causing hardening of rubber pieces that are intended to help contain that cooling air below.
Now almost 50 yrs on I see fewer & fewer "STOCK" engine configurations which you can guess usually means more heat to deal with.
Jake addressed the cooling air via his(?) DTM solution, but IMO its not very practical for stock or near stock motors (& expensive)

The go-to response to eliminate that heat is usually an additional or a remote oil cooler which comes with its own set of challenges. (IMG:style_emoticons/default/confused24.gif)
How about KISS (IMG:style_emoticons/default/biggrin.gif) Has anyone used any of the Fiberglass based stick-on reflective heat shielding products on the engine-sides of the tin?
Idea being rather than allow heat absorption to all the those steel pieces reflect it back to carried away by the cooling air?

BTW Im not a Porsche engineer...but I did stay in a Holiday Inn last night (IMG:style_emoticons/default/happy11.gif)

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.