Quote:
Originally Posted by Grady Clay
This should not be a contentious issue.
Porsche engineering staff made ‘engineering decisions’ balancing the cooling airflow through the engine (heads, cylinders and engine oil cooler) vs. the airflow through the heat exchangers.
Keep in mind that the airflow through the heat exchangers takes away cooling air from the engine.
This air is NOT previously used for engine cooling (Porsche didn't want the additional oil-leak smells).
With the air through the heat exchangers, the engineers restricted the airflow when wasting the heated air (hot weather, cockpit heating off).
This restriction was provided by the heat control ‘flapper’ valves.
The purpose of continued airflow is to maintain cooling of the exhaust inside the heat exchangers (preventing fires and over-temperature damage).
Porsche had a lot of experience with this system with “European heaters” fitted to 356 since 1963 when the 911 was being developed (and eventually 912s ).
When originally developed, the 911 heat exchangers had a fabricated exhaust system inside the heat exchangers.
This was quickly removed (recalled, thanks to Corvair experience) and substituted with the ‘S’ heat exchangers we all know and love (’64-’74) and more modern aftermarket SSI.
The more modern Factory systems have restricted airflow through the heat exchangers but enhanced with electric fans when cockpit heat is necessary.
This allows some air through the heat exchangers in hot weather (when cockpit heating is off) in order to protect the system from heat damage while not wasting too much cooling air.
In cool weather (when engine cooling is less significant issue), more air is forced through the heat exchangers by the electric fans (including the two in front starting in ’84) to the cockpit.
When you choose ‘headers’ (exhaust without heat exchangers), it is assumed that you are almost always ‘at-speed’ on track.
The airflow under the car keeps the exhaust within ‘reasonable’ (race) temperatures.
Anyone who doubts these issues should observe a 911 engine at full power on an engine dyno.
These issues resulted in the use of the “Rubbermaid Solution”.
Best,
Grady
|
I do not disagree, dispute, that if you sometimes HAVE/NEED cabin heating it is best to continue the airflow through the heat exchangers even with cabin heating OFF. With this heating arrangement you ARE diverting/bypassing a portion of the engine cooling airflow around the engine so it can do no harm, only good, in provided some amount of cooling "downstream".
But the question here is whether are not you can eliminate the need for cabin heating airflow completely. In that case the engine would always get the FULL cooling capability of whatever level of airflow the engine driven fan can "pump".