Originally Posted by kuehl (Post 7101558)

Originally Posted by wwest (Post 7101343)

On the other hand Kuehl will be more than willing to take your money, oodles and oodles thereof, for his well proven, known to work, solution.

That's the one and only reason the rear deck fans will not work in Kuehl's opinion, no money for HIS pockets.

If you're going to go ahead and buy from Kuehl, buy an add-on condensing system FIRST, that will more likely than otherwise bring the factory system operation up to acceptable standards even in Austin TX.

But even so it might be a wise move to also add the trinary pressure switch, <$50.00, both to protect the compressor from self-destruction with low refrigerant in the system and to prevent the compressor from over-pressuring the system. Assuming the add-on condensor system you choose has an integral fan, as it most certainly SHOULD, you could wire the third pressure switch such that it will run the new condensor fan as long as high refrigerant pressure persists, even with the engine switched off.

This latter effort might well prevent the system pressures from rising so high that leakage results.

Originally Posted by Scott R (Post 7101428)

Does your Lexus have an engine cooling fan?

2 actually, but YES, absolutely! Just displaced one level but effectively having the EXACT same purpose, functionality.

And is the engine in the rear under a curtain of negative air pressure? Likely not.

For the Lexus, no, but for my C4, YES!

Originally Posted by wwest (Post 7101924)

More to the point, my C4 also has an engine cooling fan that must operate, remain functional, even ith that negative air presure.

Originally Posted by brads911sc (Post 7101595)

WOW.

WWEST is a guy who lives where the average ambient in the hottest month of the year is 78 degrees...

"...AVERAGE AMBIENT in the hottest month of the year is 78 degrees...

"Average ambient", really? For what reason, other than nefarious or stupidity, would one use that term with regards the use of automotive air conditioning?

May I suggest using "average number of summer daytime hours wherein temperatures (>80F ?) clearly warrant the use of A/C."

An intelligent person might live in the northern reaches of the earth, Point Barrow maybe, and still comprehend, understand, have detailed knowledge of, the requirement of adequate A/C in Austin TX, or even at the equator. Climate does not limit a person's ability to learn nor apply that learning.

he can not speak to Austin, TX....

Makes it a real wonder that all those automotive systems design engineers in and around Detroit have been so successful, doesn't it...??

and he is educating all of us on what works and doesn't work where he doesn't even need AC

Most anyone having lived "here" for more than a few years would willingly dispute that statement, and that's not even considering those often traveling (in their air conditioned passenger vehicles) to the "dry" side, 95% VFR throughout the year.

Incl Kuehl which has hundreds of VERY happy and COOL customers who live in some very HOT and HUMID climates. If you actually look at the Kuehl site you will see many many tests with data on just about every component.

Insofar as I am aware no one, including myself, has disputed the functionality of Kuehl's upgrade solution....cost be dammed.

I would advise that you search and read all the posts that WWEST is in... there is one thing in common... he basically has told hundreds of people that they are full of BS, don't know what they are talking about, and that they are just clueless idiots who love wasting money...

Sorry, but that statement is simply an OUT and OUT LIE. My statements have been advisory, other than cost I have told no one that their solution is wrong, even Kuehl.

and that $60 in SPAL fans will cure all major ills... he has sold his fans on threads where the

presenting problems obviously could not be solved by fans.

And YOUR foundation for making the above statement is well documented? Where? Guide us if you will.

I smell a Troll but Ill let the search tool and common sense speak for itself.

I heard he and Reid were linking up to combine the latest in condenser technology and Spal fans as a comprehensive solution to all the ills of the 911 AC system. LOL

Originally Posted by kuehl (Post 7101558)

Originally Posted by brads911sc (Post 7101569)

Lol

Originally Posted by wwest (Post 7102322)

That's okay by me...denigrate the messenger, NOT the message.

RV.Net Open Roads Forum: Tow Vehicles: Ford ecoboost advice please

Yet another message worth a read, northener sticking his nose in Austin TX business.

Originally Posted by wwest (Post 7101343)

On the other hand Kuehl will be more than willing to take your money, oodles and oodles thereof, for his well proven, known to work, solution.

That's the one and only reason the rear deck fans will not work in Kuehl's opinion, no money for HIS pockets.

If you're going to go ahead and buy from Kuehl, buy an add-on condensing system FIRST, that will more likely than otherwise bring the factory system operation up to acceptable standards even in Austin TX.

But even so it might be a wise move to also add the trinary pressure switch, <$50.00, both to protect the compressor from self-destruction with low refrigerant in the system and to prevent the compressor from over-pressuring the system. Assuming the add-on condensor system you choose has an integral fan, as it most certainly SHOULD, you could wire the third pressure switch such that it will run the new condensor fan as long as high refrigerant pressure persists, even with the engine switched off.

This latter effort might well prevent the system pressures from rising so high that leakage results.[/QU
\

you mother ****er.I bet you stick yo wweewee in the exhaust pipe.

Originally Posted by kuehl (Post 7105489)

Nico,
First, an apology. Both my '78 Targa and '88 Carrera are currently on non-permanent loan to out of state adult relatives. Awaiting grand kids coming of ownership age (25?). Better than having then just setting idle in the garage IMO. So, no actual installation pictures for the moment.

See the previous post for close replicas.

I hope we are not going to far astray in answering your original question in your thread. I'm sure, however, somewhere through the amusement you will find the answers you seek.

Trying to get back on track here, to answer your question, relevant to a suggestion posted here, maybe I can provide you with some logic and facts that will help you
along the way:

The Engine’s Cooling Fan
The rear deck lid condenser removes heat absorbed by the refrigerant (in the evaporator process) via the engine cooling fan.
The 911 engine’s cooling fan pulls an average of 1335 liters per second at 6100 rpms. Actual volume varies depending upon the year; there are many quotes and charts. So lets keep it simple and say 1335 ls is fair.

Since most comparisons in air movement with fans are in CFM lets do the conversion:
(1335 per second) X (60 seconds in a minute) = 80,100 liters per minute.
Then convert the liters to cubic feet, (80,100) x (0.03531467) = 2828 cubic feet per minute. So the average 911 engines cooling fan has the propensity to move 2828 cfm at 6100 rpms.
Assuming this is linear we can further say:
0 rpm = 0 cfm
1525 rpm = 707 cfm
3050 rpm = 1414 cfm
6100 rpm = 2828 cfm
or simply 46 cfm per rpm

Obvious typo, should be 0.46 CFM.

And let's assume at idle of 850 rpm, the cfm is equal to 391 cfm (850 x .46).

What Could You Put Under the Deck Lid Condenser
The typical 911 condenser is 9"x27.5" of effective area, or 247.5" sq in.

Ideally the largest diameter pancake electric motor puller fan you can mount under the condenser is a 9" nominal.

"..Ideally..." No, I used 12" fans with sheet metal blocking the fans' overlap intake area.

The inexpensive red colored fans posted in the thread boast a CFM of 1730 (we will assume at 0 static pressure) and consume 12 amps each?

CFM = 1550 x 2 = 3100 CFM. 7 amps.

I’m going to shoot from the hip here and I will say BS.

After testing dozens cheap and inexpensive fans over the years,

"...cheap and inexpensive..." Inexpensive, yes, CHEAP unwarrantably implies poor quality. The fans I used are from the very same manufacturer as used by Lexus in my '92 LS400, '95 LS400, and my '01 F/awd RX300. Just didn't the Lexus dealer's price.

and knowing that many Ebay seller’s claims or test data can inaccurate (for many reasons), I would want to ‘see this for myself’ as they say. So lets take a reputable fan company such as Spal and exam their PN 30100442; a 9" puller that moves 649 cfm at 0 static and draws a 6.1 amps at 13 volts. under 0 static pressure. So at “idle”, you could have an electric cooling fan pulling 60% (engine fan 391 cfm/ electric fan 649 cfm) more air !

In my case that would be 3100 CFM vs the engine's 391 CFM. But to be fair the 3100 CFM should be derated to maybe 2500 CFM due to the only partially functional overlap area outside the condenser area itself.

Wow, 634% more airflow...

How Effective Could Electric Fans Be?
Any given fan never pulls across the entire deck lid condenser. Effectively 1 fan does not pull a 9" of diameter, or 63.6 sq in, across the surface because the fan’s motor area is typically 4.375", or 15 sq in (no fan blades), so the effective surface the fan works on the condenser is 48.6 sq. in each. Let's multiply that by 2 fans for 97" nominal sq in of working area, or 39% of the condenser area. At idle, if you have a 60% increase in air volume working on only 39% of the condenser area, the net effect might be .... .60 X .39 = 23% in total improvement for that condenser... at idle. And then you have to wonder if the engine’s cooling fan will allow that 23% increase in air move through it? Well all calculations thus far have been with a foundation of 0 static pressure. So we will have to think about it. And, in the world of AC, a 23% increase in air flow, at 0 static, usually does not mean your vent temps will drop by 23%...

that is another set of equations.

No kidding....two 12" fans....cover a LOT more of the total condenser area than would two 9" fans as you propose/used.

At Idle
“At Idle”. For some drivers, ‘at idle’, might mean sitting in the car after a long day of work, waiting and hoping the vent temps will get cool quickly. “At idle” could also mean coming to traffic light or a stop sign. So how may driving hours do you do in a given day? How many minutes of your average trip or joy ride are really at idle? That varies for most however lets assume you are taking a 60 minute drive. Is 10 minutes fair to say? I’d say on the extreme maybe “yes”. So if you want a possible 23% increase at best in rear deck lid condenser cooling performance, at idle, maybe you might try to Sepal Fans. But then again... read on.

It appears, truly, that you have little or no experience driving a car in and out of a major city downtown core during rush hour. Then add an accident 2 or 3 times a month....


Above Idle, The Real Ride Losses

Above idle... what most of us spend doing, say driving around town between 25-40 mph, what are our engine RPMS’? For me it is usually above 2000 rpms for sure.

"..for sure..." Inexperience CONFIRMED!

Looking back at our estimate of engine cooling fan speed cfm’s we calculated that then engine cooling fan is likely moving .46 cfm for each rpm. So 2000 x .46 = 920 cfm moving through the engine deck lid without add on electric cooling fans.

The add on electric cooling fans, at best, could move 649 cfm.

No, in my case closer to 2500 CFM vs the engine fan's 920 CFM, still a 250% improvement.

That is less than the engine’s cooling fans! So what happens? Dam it!
That’s right, Dam It happens.

In my case that "DAM" doesn't become an issue until the engine RPM rises above 5434

Those electric cooling fans are now blocking or damming the work of the engine's cooling fan. Not by 100% though, but enough to cause a reduction of air pulled in by engine cooling fan. How much? We know the 2 electric cooling motor housings total 15 sq. in. . The 2 sets of motor blades account for an approximate 45 sq in. So in total 15+45 = 60 square inches of direct blow through blockage potential. The deck lid condenser is 247 square inches. 247-60 = 187". So there is a loss of 24% of your deck lid condenser working area, (187 / 247 = .757) = 24%, when you attach two 9"fans ...when ever your engine rpms are above ? .... 649 cfm/.49 = 1324 rpms !

Just how much time, or how often, do you have the engine RPM above 5434 (my case)

The Choice is Always Yours!
A) Do not add cooling fans to the deck lid condenser, and simply realize that an increase in engine rpms above idle allows the engine cooling fan to pull more air through the condenser, as well the compressor pushes more refrigerant through the system.
B) Add cooling fans to the deck lid condenser, and when ever you take a drive, your deck lid condenser will be working 24% less efficient for most of your driving time.
C) Add cooling fans to the deck lid condenser, and just sit in your car, in your driveway,
and keep the idle below 1324 rpms, realizing that you at least accomplished something for the moment.

And, as always, everyone, including Wwest, are welcome to comment on the simple math, or provide their own math equations, estimates, data, or whatever floats your boat.

In the mean time, have an enjoyable Thanksgiving, realizing that every pound of turkey, stuffing and desert you consume is equal to 6.073 pounds of petrol.

Signing off for now. Time to do an oil change in preparation of the upcoming NY/NJ/CT/PA annual Thanksgiving Run, where I'm guessing well over 50 fellow Porsche owners will hopefully remember the elevation of the 'cliff corners' at the Delaware section of the 97 drive is well over 100 feet straight vertical drop to the 43 degree water, AND, the final destination (bar and grill) only seats 50.

Musical chairs !

Originally Posted by kuehl (Post 7105681)

OMG! Wwest!

The condenser is a rectangle.
If the width of the condenser is only 9"
putting a 12" diameter fan, if you could fit it,
is silly.

Silly..? No. The idea was to cover as much of the condensor area as is possible, if 13" fans would have fit...

Believe me you.... if I knew fans worked I would have bought a factory that makes them 15 years ago.

But I would bet that should the idea have occurred to you 15 years ago you would today be the proud owner of that factory.

At least post something like: "well, at least they may work at idle when (you) are sitting in your driveway".

Really,,, get a grip.

Originally Posted by kuehl (Post 7105944)

1) The CFM rating you are reporting on your 12" x 2 fan, of 1550?
No way. What you are probably reporting is not CFM but rather m3H (meters per hour). You need to multiply the 1550 by .59 to convert it CFM.
In which case each of your 12" fans is pushing only 914 CFM.
However A Spal brand 12" only pulls 856 cfm static at 6.4 amps
So you know your 1550 is meters not feet.

See post # 38.

2) Its logical to see that you getting carried away here.
Just look at the AMP draw data and CFM rates from
Top Street Kings Ebay advertisement, it can be confusing.
This is why I prefer to look at a reputable company like
Spal; I'm usually on the phone with their tech people several
times a year.
Anyway your Top Street King buddy is stating 1750 CFM, 12.70 amps.
What they really mean is 875 cfm 6.35 amps per unit. I believe
their amp draw by i feel their cfm is over rated especially on a straight
blade fan. Comparing what they are peddling to reputable manufacturers
I bet they are closer to 600 cfm at best.

I refer you yet again to post # 38...horses mouth as it were.

Wwest, if you like your fans then jolly good for you.
If you think your fans work, then jolly good twice for you.
If you want to believe in things that are not real, stay with
it. You need a pacifier.

And no, I did think of and review the idea (fans) 15 years ago.

Had I had the slightest positive thought about it being worthwhile in a 911
we would have published it in the The Mr. Ice Project and we would be marketing it for the 911.

Enjoy your holiday .... Turkey!

Originally Posted by wwest (Post 7106254)

Spal 12" dual 3168CFM >$345.00


Spal 12" Dual High Performance Cooling Fans (PAIR) w/ Shroud 3168CFM | eBay

Originally Posted by brads911sc (Post 7106283)

Nice. Except you are missing the entire point. :confused:

The question is not whether you can marginally improve the airflow at idle.

I don't think a ~600% improvement in condensor airflow would ever, or should ever, be considered marginal.

Who cares if you can?

So, now that I have clearly won, FACTUALLY won, the first cause we're now going on to the next one...?

The issues that needs addressed is adding more heat to the engine and fixing inadequate components. In this case every CFM of hot air you are drawing in through a hot deck condenser is being pulled down over your already hot engine struggling to stay cool at any RPM where this would make a difference.

If this was a good plan we wouldnt be putting oil coolers with fans in fenders.

The reason "we're" putting oil coolers with fans in fenders is because Porsche realized that as the engine's power producing capacity rose air cooling alone proved to be problematic.

At the end of the day... your Spal fans at any CFM dont address this issue.

How can you be sure of that, how can anyone? Considering the extreme volume of air the fans move relative to the engine fan, 6:1, might the net effect be positive, improved condensor AND engine cooling.

The heat needed to be removed, to have ice cold AC, in 95 degree ambients seen in Austin will exceed what you could add to the engine bay without increasing engine temps.

Interesting thought...The heat load will be worse during the initial cabin cooldown, right..while the engine is initially heating up. Might the faster risetime of the engine heating up extend the engine life...?? And once the cabin is cooled down to your satisfaction just what is the continuing level of heat load on the engine from the BTUs extracted from the condensor...?

Been there, done that... unless you are ok with 10 oclock engine temps..

I'd have to ask Porsche's position on that, were it to actually be the result.

It also cant address the numerous issues with 911 AC that these fans dont solve... Like poor evap performance, inadequate air volume over the evap, the inefficient and leaking non barrier hoses, the inefficient front condenser, and the generally poor tube and fin design of the deck condenser. All of these all up to a system that is woefully inefficient in which ambient temps over 90 only make your solution worse for the over all performance in which heat is 1 factor.

As Griff has said, I am glad you have it all figiured out for Seattle. For the rest of us where its still 80 degrees today in mid November... We will realize that you just really dont have a a good understanding, and that the easiest way to stay the center of attention is to sell fans...

Oh, and you have been selling $60 fans for the last 3 years. Not $345 fans.

The spal fans were initially introduced to this thread by Kuehl. I brought up as a subject only to dispute kuehl's position that I was misquoting the CFM rating of the $60 Ebay fan set. I would NEVER suggest buying a product for its brand name only when exacting clones are so readily available in the marketplace at 20% of the cost.

I can buy a ZIMS fender kit with a 12 inch fan for $500

Again, $60 is the competing amount, ~$200 if you install the trinary pressure switch and arelay or 2.and not

drop all that heat in my engine.

Can you quanify that statement..?

My guess would that with our A/C operating acceptably the system BTU output rating might be no more 12,000 BTUs. that would be about 4,000 watts at full bore. Once the cabin has cooled down that number should drop to about 1000-1500 watts. Numbers, approximations, taken from our 28' MH.

Thats $165 difference. So youd rather have 10 oclock engine temps instead of below 9 oclock to save $165?... That my friend is stupid...

You're the only one ASSuming that 10 oclock position would be detrimental to the service life of the engine. Personally I suspect the condensor cooling fans ould be more of an asset, more engine cooling overall, than otherwise.

Have a great Thanksgiving.