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)

[914werke]

Coming from a background in general aviation...I suggest you're overthinking it.

Our cooling systems are ridiculously simple. It's not "laminar" flow in any sense of the word, that air is coming and going all over the place. Our cooling systems are nothing more than dumping as much air as possible to the top of the engine so that it flows to the lower pressure bottom side, taking heat with it.

You can either increase the pressure on top, or decrease the pressure below. Or both. Either will improve airflow and BTU scavenging.

Overthinking it... quite possibly. (IMG:style_emoticons/default/biggrin.gif) But Im thinking your characterization of the the T4 air cooling flow is probably ... a bit harsh (IMG:style_emoticons/default/laugh.gif)

Musing a little more...
On the early 1.7L's they had a funky oil bath air filter element & a.... pre-heater system.
The heat was derived from a duct attached the rearmost cyl. tin (#1) & ...via flow of air from front to back of motor forced by the Impeller. (IMG:style_emoticons/default/confused24.gif)
Why not use that same design application to, if as you say, dump cooling air to the rear cylinders on both sides ? You could use the Fan that is already in the Eng bay for additional flow? (IMG:style_emoticons/default/rolleyes.gif)

[Superhawk996]

You could use the Fan that is already in the Eng bay for additional flow? (IMG:style_emoticons/default/rolleyes.gif)

Might not be quite that simple.

You need to be conscious that pressure differential dictates direction of airflow.

Example: if the auxiliary fan isn’t running - the engine fan will blow air out of the auxiliary fan - decreasing airflow available to the engine.

Similarly if the auxiliary fan was able to overpower the engine fan you could end up with degraded cooling. Not likely but something that should be considered. Probably would want a one way flapper on the aux fan to prevent that sort of reverse airflow - similar to the little flaps down on the heat exchangers.

What complicates this is that the engine fan is operating at variable speed while the auxiliary electric fan will operate at fixed speed. Might be hard to ensure the balance never results in airflow being pumped in the wrong direction.

[DRPHIL914]

You could use the Fan that is already in the Eng bay for additional flow? (IMG:style_emoticons/default/rolleyes.gif)

Might not be quite that simple.

You need to be conscious that pressure differential dictates direction of airflow.

Example: if the auxiliary fan isn’t running - the engine fan will blow air out of the auxiliary fan - decreasing airflow available to the engine.

Similarly if the auxiliary fan was able to overpower the engine fan you could end up with degraded cooling. Not likely but something that should be considered. Probably would want a one way flapper on the aux fan to prevent that sort of reverse airflow - similar to the little flaps down on the heat exchangers.

What complicates this is that the engine fan is operating at variable speed while the auxiliary electric fan will operate at fixed speed. Might be hard to ensure the balance never results in airflow being pumped in the wrong direction.

@Superhawk
@914werke
-simple thoughts from a simple mind) (IMG:style_emoticons/default/idea.gif) (IMG:style_emoticons/default/rolleyes.gif)
i probably need to go back and absorb better some of what you posted i just skimmed it, but thinking about the different things here just a couple thoughts and questions,
and i am not an engineer nor did i stay in a holiday inn express last night, although i might tonight so i might have better thoughts on this tomorrow, (IMG:style_emoticons/default/lol-2.gif)
but for now,
my first question is about the air flow and pressure pulling/pushing air over the cylinders. It seems that the back side of the motor is a dead end, and so as mentioned before by others turbulence ensues, flow is disrupted , reduced heat exchange and extraction, if its + above and - below, can an additional fan below pulling air from above, or creating negative pressure how ever you want to say it, could this help? just like our pulling fan on the aux oil cooler? I mean a 50 degree reduction in head temp from acouple of 3/8" holes?? might not got hru the trouble of other approaches if its really that simple, but would a fan under pulling air from thetop down over and out help? seems it might.-
- thought #2: regarding the air from from the front impeller and the use of heat exchangers- is it possible that any air flow being directed out the bottom to the j-tubes and thru the heat exchanger(especially in warm weather when its not needed), if the little flapper is open and letting air go out below instead of all the air being directed over the top of the motor, this would in the heat of the summer hurt the effectiveness of cooling the top of the motor, less air flowing thru the top.

- also i watch my head temps and oil temps and you do see that when the oil finally gets full circulation as the aux cooler thermostat open and the extra oil flows the head temps decrease, ( in answer to another persons question about oil effecting head temps, yes it does)
-i have a 2.1 motor - i run 20/50 oil( high zppd valvoline dino oil )and higher compression etc so having the auxcooler is a must, even in 80 degree weather down in Amelia Fl a few weeks ago, my fan was not turning on so those oil temps went up a good bit idling in traffic, no air flow over the Aux cooler, i think it was around 230, but next stop i fixed the wiring to it and got it working and after that even sitting in traffic, and also under harder driving, it never went over 210, and head temps btw in this situation also were reduced.
I have new tin and alll new tin with new seals, spark plug hole seals in place etc. so just keeping it to the air flow issue, seems that allowing air to go out the lower side hurts flow to thetop, and maybe a fan under sucking air from the top could help? other wise any way to get air to flow better over theback side of the motor from top down should help - id like to see a picutre of where those 2 3/8" holes were placed as well.


Phil