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Old 05-05-2021, 11:37 AM   #1 (permalink)
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Cooling systems, 'complex and difficult'

MOTOR TREND hot-lapped the 2012 Porsche 911 Carrera S, at Laguna Seca Raceway, Monterey, California, USA. They use a trio of V-box, GPS dataloggers, accurate to 1/1000-th of a second for their quanta.
The following are data presented, and my dirty math:
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* Lap time 1: 39.30, ( 1.655-minutes )
* 36.2537-laps / hour equivalent
* @ 2.238-miles / lap = 81.1357-miles per hour average velocity
* 131.194-mph estimated maximum track velocity, between Turn-11, and Turn-1 ( from relationship to other Carreras also tested there )
* 'Blower-assisted' cooling drag associated with fan losses, motor losses, alternator losses, seven-pulley serpentine belt-drive losses, and engine losses = 4.307-horsepower at the fuel tank
--------------------------------------------------------------------------------------
* Plugging 4.307-horsepower into the drag power formula at 131.194-mph, and solving for CdA, yields a 'blower-assisted' cooling drag - equivalency of CdA 0.2794 square feet during track mode.
* Adding to the CdA of the low drag Carrera yields CdA-e 6.1263-square-feet.
* Dividing by Porsche's Af = 20.8819-square-feet = Cd 0.2933
* Cd 0.2933 - Cd 0.28 = Cd 0.01338
* Cd 0.01338 + Cd 0.003 ( original 'high' Cd cooling system ) = Cd cooling-e 0.01638 ( 5.85% of total drag ) vs 1.07% total drag reported by Dr. Thomas Wolf.
* A 546% increase
--------------------------------------------------------------------------------------
* Along with the Cd 0.002- 0.003 cooling drag mentioned for the MY 1997 Carrera, which became the template for later generation Carreras, Dr. Wolf DOES mention the ' blower-assisted' drag, however, it is not accounted for in the wind tunnel data.
* It requires a 'look' at the fuel tank in order to 'see' this additional drag, which has been exported away from the cooling system.
--------------------------------------------------------------------------------------
* Like I said, this is just dirty math, back of the envelope stuff, however, this type of consumption must be accounted for on the Carrera's energy ledger sheet.
* Until this car came up in discussion, I was unaware that, any passenger car would rely on artificial airflow when at 40- mph ( 64.4 km/h ) or above. Typically, the dynamic pressure alone is sufficient for cooling.

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Old 05-05-2021, 11:49 AM   #2 (permalink)
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* 'Blower-assisted' cooling drag associated with fan losses, motor losses, alternator losses, seven-pulley serpentine belt-drive losses, and engine losses = 4.307-horsepower at the fuel tank"

Since so much in this discussion appears to hinge on the above number, how was it arrived at? My gut feeling, it seems low?
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Old 05-05-2021, 12:03 PM   #3 (permalink)
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Quote:
'Blower-assisted' cooling drag
Is this the fan employed by every air-cooled Porsche and VW?

Quote:
...this additional drag, which has been exported away from the cooling system./4.307-horsepower at the fuel tank
What is this, I don't even...
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Old 05-05-2021, 12:15 PM   #4 (permalink)
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how

Quote:
Originally Posted by j-c-c View Post
* 'Blower-assisted' cooling drag associated with fan losses, motor losses, alternator losses, seven-pulley serpentine belt-drive losses, and engine losses = 4.307-horsepower at the fuel tank"

Since so much in this discussion appears to hinge on the above number, how was it arrived at? My gut feeling, it seems low?
I'm going to sit on my numbers for awhile.
The official cooling system data is available from Porsche, online.
I reverse-engineered my final estimate using efficiencies from scattered sources.
For anyone actually interested in the topic, I'd like them to work with what they have, and we can compare numbers after.
There is no 'right' answer. Just 'guestimates.' 'Ballpark figures.'
The concept of the thread is the point I wanted to make. Not absolute numbers.
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Old 05-05-2021, 12:28 PM   #5 (permalink)
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Is this

Quote:
Originally Posted by freebeard View Post
Is this the fan employed by every air-cooled Porsche and VW?


What is this, I don't even...
1) it's different
2) passive-cooling is inadequate with the Carrera. It requires 'supercharging', if you will, in order not to 'Chernobyl' the engine.
3) the Carrera is not tested on a chassis dynamometer, within the wind tunnel, under acceleration g-forces, deceleration g-forces, lateral acceleration g-forces, aerodynamic forces, and rolling -resistance, with the engine running, in gear, as would be encountered on a pavement race track.
4) the artificial ' blower-assist' energy is not accounted for. Although the universe experiences the loss.
So we're looking at a book-keeping issue.
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Old 05-05-2021, 12:51 PM   #6 (permalink)
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Delco Remy, 2008

Here's a paper with some values:
https://www.delcoremy.com/documents/...ite-paper.aspx
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Old 05-05-2021, 02:32 PM   #7 (permalink)
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Quote:
1) it's different
2) passive-cooling is inadequate with the Carrera. It requires 'supercharging', if you will, in order not to 'Chernobyl' the engine.
The provided link does not show how it is different, it appears to address alternator efficiency. I decided to answer my own question and got this far:

https://www.researchgate.net/publica...he_911_Carrera

Quote:
Inspite of the roughly 15% increase of the cooling-air flow through the radiators, it has even been possible to reduce the cooling drag level of the new 911 to below that of the predecessor model. The low cooling-air losses of the 911 are primarily due to the integrally designed cooling-air ducting from the inlet to the outlet openings, the large radiator areas, low internal pressure losses and mainly to the control of the cooling-air mass flow rate and cooling drag through the clearly reduced outlet cross-sections.
I just skimmed this but no mention of a blower?
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Old 05-05-2021, 02:49 PM   #8 (permalink)
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different

1) the Carrera's radiator chosen, was thermodynamically superior to what it replaced ( a non-aerodynamic modification ).
2) 'blower-assisted' horsepower was increased 25%. ( a non-aerodynamic modification ).
3) Coolant temperature was allowed a 10% excursion ( a non-aerodynamic modification ).
--------------------------------------------------------------------------------------
4) much of what allowed the Carrera to have a smaller cooling drag footprint had nothing to do with aerodynamics.
5) Dr. Wolf admitted that, in a 'track' environment, the dynamic pressure would be inadequate to protect the engine from overheat, requiring the 'blower-assisted' increment.
6) This 'blower-assisted' cooling isn't reflected in the car's drag coefficient. It's different from most cars.
7)On most cars, above 40-mph, you could throw the cooling fan away, and the car would be just fine. I've done this.
--------------------------------------------------------------------------------------
8) if you take the portion of energy actually required to cool the Carrera, it is equivalent to increasing the cooling drag coefficient, by approximately 546%.
This is what got me shaking my cage.
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Old 05-05-2021, 05:07 PM   #9 (permalink)
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From the paper:

The primary engineering target, however, was to guarantee a sufficiently high cooling
capacity regardless of the driving condition. For sports cars, “circuit racing“ and „highspeed driving“ are the most relevant operating modes with the highest loads on the cooling system occurring during blower-assisted operation on racing tracks. During aerodynamically relevant high-speed driving, the demand for cooling is considerably lower. The different cooling-capacity and cooling-air demands under those operating
conditions had to be taken into due account. And in order to realize a most efficient and demand-adapted cooling-air concept it was important not to overdimension the
cooling-air requirements either.


So all this bumf from Aerohead is just because on the track (not at high speed on the road) the radiator fan comes on?

Really? That's some great conspiracy that only Aerohead can reveal?

The rest of us can admire a car whose design gives extremely low aerodynamic cooling drag.

Talk about losing the wood for the trees.
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Old 05-05-2021, 05:28 PM   #10 (permalink)
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So what do you think? Is the 'blower assisted cooling' just a radiator fan?

I get the part about right-sizing the ducts.

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