Flat fans, revisited

[911pcars]

This is a continued discussion from a thread on lightweight rocker arms:
http://forums.pelicanparts.com/newreply.php?do=newreply&p=5119566

Originally Posted by Steve@Rennsport

Hi Sherwood,

Walt is right,...it takes about 30HP+ to drive the Porsche flat-fan. This was well worth it on our 935's, but having 600-800+ HP, it was not an issue. The big reductions were cylinder head temps which established how much HP we could make,....

My apologies for the digression.

Hey Steve,
Can we extrapolate the following?
If:
30+ HP for 600-800HP
then:
X HP for 200-300
Would it be 1/3 to 1/2 (10-15 hp)?

What's the loss from the existing vert. fan, belt drive?

Is a gear drive the optimal drive system? Is there an optimal fan configuration for all engine speeds?

For starters, here's a Wiki article on propellers (e.g. fan blades) that contains some interesting facts.

Sherwood

[Shaun @ Tru6]

Coolness factor of a mechanically driven fan aside, why can't the fans be electric with speed variation determined by head temp?

[wp935]

There is also the visual cool factor of the flat fan motor ..........

[911pcars]

This is an interesting discussion on the Cal-Look forum re: the SCAT porsche fan kit:

FWIW, notice the 911 fan adapted to horizontal configuration and opinions as the efficiency of the 911 air shroud:

SCAT porsche fan kit | The Famous California Look Beetle and Classic VW Car Forum

Sherwood

[Brando]

I'd be interested if there is a flat-8 conversion kit to go with the fan

[RWebb]

any fan is "expensive" in terms of a parasitic load on the engine

here is another tidbit:

On the 1963 911, the cooling fan took only 4.7% of the 901's gross engine output - Ludvigson, EXCELLENCE WAS EXPECTED, 1st ed., Ch. 16, p. 402

I should have some data on fan vs. water pump for VW motors somewhere - will post if I get a chance to search for it...

[RWebb]

ok, found it:


Flat fan (e.g. 935) required » 30 hp

a water pump consumes about 12 to 15 hp at 6000 rpm for a Chevy LS1 motor

On the VW Vanagon, the crank-driven fan required about 3.4 hp of the 67 maximum on the air-cooled motor, for a reduction of 5.1%. The water pump on the water-cooled motor, requires only 0.7 bhp of the total 82 hp, for a reduction of only 0.08%.

the VW info is from Rod & Truck, June 1985

[juicersr]

Be the first on your block for a mere $12,000 (plus shipping) at todays rate of exchange

Parts and Spares

[khamul02]

Man, I would like to just have that carbon fiber fan for the lack of maintenance.

[RWebb]

Originally Posted by khamul02

Man, I would like to just have that carbon fiber fan for the lack of maintenance.

[khamul02]

How much?

[dfink]

Does anyone know the actual required CFM to cool the engine. At some point I would think you are just shoving air with no return. I have thought perhaps a horizontal mounted electric fan would move enough air but don't really want to be the experiment. There must be some engineers out there that know how to calculate the CFM required. Much of the air on a stock engine goes out the heater dumps.

[David]

The system is so simple and efficient now (belt and magnesium fan) that it's hard to improve on for most applications.

There are issues like the magnesium in the fan and housing failing, but this is mainly in the housing. And there are aftermarket solutions.

[jcge]

Originally Posted by dfink

Does anyone know the actual required CFM to cool the engine.

Here's a couple of data points - I'm sure others could build on this from the various spec books/workshop manuals - also depends on auxialliary oil coolers...

993 fan blows 1010 litres per sec at engine speed of 6100 rpm (at max power) with pulley ratio of 1.16 (reference Porsche tech spec book)

2L 911S fan blows 1390 litres per sec at engine speed of 6100 rpm (max power at 6900 rpm) (reference Porsche workshop manual)

And some racing engines with flat fans.....

908 3L 8 cyl = 14hp (ref Mezger IME 1972)

"the cooling properties of the 917
12-cylinder engine are superior to all of Porsche’s earlier
air-cooled racing engines. This holds for the engine
temperatures as well as for the power requirements of the
cooling air blower drive" (ref Mezger IME 1972)

"The cooling blower is arranged horizontally above the
engine. It has a diameter of 330 mrn (13 in) and supplies
the cooling air for the engine at a rate of approximately
2400 l/s at the rated engine performance. The blower is
driven via bevel gears at a ratio of 17: 19 of engine speed.
As already mentioned, at maximum engine power the
power input to the blower is 17 hp, i.e. 2.7 per cent of the
engine performance. Of the entire cooling air volume
65 per cent is used to cool the cylinder heads and 35 per
cent for the cylinders." (ref Mezger IME 1972)


John

[sc_rufctr]

Originally Posted by juicersr

Be the first on your block for a mere $12,000 (plus shipping) at todays rate of exchange

Parts and Spares

Cool set up but $12,000??? That's a bit steep.

I would have thought around $4,000 would have been reasonable.

[Steve@Rennsport]

Its VERY important to realize that an air-cooled engine needs a LOT of air to keep the heads cool as thats the key to maintaining power. This has always been the struggle and the latest 930 fan setup (245mm & pulley) is the closest thing you'll get to the flat fan.

Flat fans were intended for engines that ran high cylinder head temps and for those app, its a godsend (but not anywhere close to water cooling). You just cannot get enough airflow to keep them cool enough (under 225 deg F) for best VE. This is precisely why Grady did his "Rubbermaid Solution" on his race engines.

A local gent used a 935 flat fan to cool his 410+ HP, 3.5 litre race engine and IMHO, it was worth the power loss to maintain full output on hot days at the track.

[Steve@Rennsport]

Originally Posted by sc_rufctr

Cool set up but $12,000??? That's a bit steep.

I would have thought around $4,000 would have been reasonable.

Peter,

We recently sold a 962 CF flat fan setup for $20K and knowing whats involved with these components, it was worth every dime.

IMHO, $12K is a genuine bargain for everything pictured. I couldn't do it properly myself for savings.

[island911]

Originally Posted by khamul02

Man, I would like to just have that carbon fiber fan for the lack of maintenance.

CF would have a chewed leading edge in no time.

Jet engine tests were made using CF compressor blades. Worked great until they landed in dust storm. The compressor blades became CF brooms.

[sc_rufctr]

Originally Posted by Steve@Rennsport

Peter,

We recently sold a 962 CF flat fan setup for $20K and knowing whats involved with these components, it was worth every dime.

IMHO, $12K is a genuine bargain for everything pictured. I couldn't do it properly myself for savings.

Steve

With all dues respect but...

I understand an original set-up would be $20k... After all it is original.
But my reply was based on all of these parts being manufactured/sourced new for this kit...

Here is the list of components I can see in the picture.
I think I've been somewhat generous and reasonable in the cost of each component... IMHO!

I understand that they wouldn't sell many of these kits but it still seems expensive to me.

Alternator - not included

Fibreglass fan and shroud - $2500 (not CF because I'm a traditionalist)
Coupling,gaskets, Bits - $ 300
Belts - $ 150
Pulleys - $ 250
Red shroud and cone - $1500
= $4700...

Strap mount and Bevel drive in one - No idea... but I is it worth $7,300?

[matty74]

wer'nt the flat fan engines coupled with water cooled heads or was that just the 956/962