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)

[GregAmy]

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.

We all agree on one method to decrease below pressure, and that's to ensure the firewall plastic flapper thingies are in good nick. That deflects undercar airflow, causing turbulence in the engine compartment, reducing underside pressure.

You could seal all the edges of the tins on the upper sides, like maybe using aluminum ducting tape, to seal off areas where pressure may be escaping.

Another method is to relocate the oil cooler so that you can remove the cooler flappy thingie (I love my technical terms) which, in my mind, is partially responsible for the differences of CHTs between #3 and #1 (another factor could be the direction of axial/radial flow from the front fan).

Our stock cars have additional surrounding seals to block hotter underside air from creeping up and being recirculated into the cooling intake fan (and induction). Delta-P and Delta-T, and all that.

One of the tricks that the 4-banger 914 racers used for SCCA Production racing was to run a large dryer hose going all the way forward to one of the headlight door holes to provide cool ram air to the front of the stock engine fan and housing. Chris Foley could show you a photo of that.

Material of the engine covers is likely insignificant. If your cooling system is working well, the engine tins should be relatively cool to touch, since they are constantly being cooled by airflow. They will be hot due to conduction from the engine, but not as hot as they would be if there was no airflow...

An GA airplanes, we always talk about ensuring that the upper engine compartment area is sealed really well, so that incoming ram air can adequately flow down through the cylinders and heads to cool things down. Every time someone complains about increased CHT (when operated within parameters) it's almost always due to significant leakage through degraded (or even missing) engine compartment seals.

Not-so-ironically, one of the cooling improvements in some Experimental aircraft is to add a containment box over the top of the engine, just like our cars, so that you're not depending on the engine compartment door, seals, and such to contain and direct that upper ram pressure.

Finally, since a lot of us are increasing the BTU output due to modifications, then ultimately we'll hit a BTU-scavaging limit of the current system...and that's when we start looking for alternate designs.

I say just make sure your stuff is in good shape. KISS, right? - GA