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Quote:
Originally posted by Wil Ferch
One can then ( conceivably) have the wrong "outer" half attached to the fan's inner half. Different fans not only have different number of blades and diameters...they embody different "pulley-half" diameters ! Beware.
that's interesting.
I use the high ratio 5 blade outer pully half on the large 11 blade fan. I figure that the large 11 blade Never had the high ratio. I've never noticed any problem with belt attachment at the fan. I have no experience about other crank pullys besides the stock high ratio pully. ie: what would happen if using another crank pully on the high ratio fan pully. I just found out on this thread that the crank pullys are different.
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Old 07-01-2004, 10:07 AM
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The pulley halves may or may not have differnt dimensions but they are certainly functionally compatible. I used my '76 1.8 pulley half w/ my'84 Carrera fan for 10yrs and 50k mi w/o any issues what so ever.
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Old 07-01-2004, 02:36 PM
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I think a big part of whether a "mis-match" works ( or not)....is if you're using a 83 / 80 pairing.... vs a 80/95 or 83/95 pairing.

As I said, I can't imagine why Porsche even made differently sized pieces that were so marginally different. The number of adjustment shims used may have a more pronounced "ratio" affect than whether you're running a 83 or 80 pulley.

--Wil
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Old 07-02-2004, 05:36 AM
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Lightbulb

OK, I know that most of the guys with increased capacity street motors are looking to increase air flow to keep their engines cooler. I'm looking at going the other way with my small capacity (~2.3 liter) race motor (up to ~7800 RPM, most of the time spent between 4000 and 7800 RPM). The objective is to not draw too much air at higher RPM's in order to save HP. The engine will have a bumper mounted oil cooler so I'm expecting the cooling to be sufficent.

Rather then get a relatively rare 225 mm 11 blade fan and run it with a 1.3:1 hub, why not use a 5 blade 245 mm fan with a 1.3:1 hub. In a 2.7 at 6700 RPM the 5 blade fans have a tip velocity of around 9000 M/S. The 11 blade fans all seem to see maximum tip velocity of about 7800 M/S. The early S's and RS's had the slowest peak tip velocity of about 7200 M/S at 7200 RPM. The SC's on the other hand had tip velocities of ~7600 M/S at 6000 RPM for the '78's and '79's, and ~7760 for laters SC's at 6000 RPM.

Using a 5 bladed fan with a 1.3 hub should be pulling about as much air at 7800 RPM as a stock 2.7 pulls at 5700 RPM.

Does anyone have an airflow chart for a 5 bladed fan?
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Old 01-15-2005, 04:36 PM
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bump
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Old 01-17-2005, 02:39 AM
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oil temps and head temps are 2 very different things

the smaller 226mm fan and shroud from the '78-79 SCs are plentiful and fairly cheap.
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Old 01-17-2005, 05:14 AM
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Quote:
the smaller 226mm fan and shroud from the '78-79 SCs are plentiful and fairly cheap.
When was the last time that you saw a set loose or on-sale?
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Old 01-17-2005, 05:23 AM
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Have you contacted the usual dimantlers?
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Old 01-17-2005, 05:30 AM
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I have the same question. It took me quite a while to find a 225 mm fan. I would just love to find another. Any leads?
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Old 01-17-2005, 05:32 AM
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I have wanted to replace my 5 blade fan for some time now.
Yesterday I found an 11 blade fan and bought it. Never thought about that there could be so many 11 blade fans.... I just made sure it was 245 mm.
Now I have it in my hands and it looks like its the early 11 blade fan with the 95 mm pulley.
How can I use this?
I need a smaller crank pulley, I guess. They are HUGE $$$ I see now, Fuchs.

BTW: I cant find a Porsche number, or any markings on it, where should it be?
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Old 12-04-2006, 08:52 AM
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Been thinking. Since I have the 130 mm 5 blade crank pulley I should be able to use the new fan. It will turn slower than my 5 blade fan but faster than it would with the original 110 mm pulley so I should get a lot of air from it.

My concern now is what length of fan belt to use. How do I calculate that?
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Old 12-04-2006, 11:16 PM
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Belt size is usually 2x length of crank center to fan center ...plus....1/2 circumference of each pulley....

- Wil
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Old 12-05-2006, 06:08 AM
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Quote:
Originally posted by Wil Ferch
Belt size is usually 2x length of crank center to fan center ...plus....1/2 circumference of each pulley....

- Wil
OK, thanks.
You don't see any problem with using that fan and pulley?
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Old 12-05-2006, 06:30 AM
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I've never personally made that modification. But if you look at all the combinations from my 6/30/04 post of 2:49 PM....you should see that the overall air flows did not change ALL that much ..sure, there are improvement potentials.

Your issue will likely be physical mounting, and correct belts....more so than air flow, etc.

- Wil

PS - this might be of interest to you too--> Poly belt pulley sources
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Last edited by Wil Ferch; 12-05-2006 at 06:51 AM..
Old 12-05-2006, 06:49 AM
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is the math funny with these ratios? if you divide each crank pulley number by each fan pulley number, it doesn't jive...

110/95=1.15 supposed to be 1.3
130/80=1.625 supposed to be 1.8

or is it that the pulley size is only the physical size of the steel, and not where the belt actually sits?...

even subtracting some to make a smaller effective diameter leads to...
100/85=1.17
95/80=1.18

what gives?
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Old 12-05-2006, 11:43 AM
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I've seen that too....don't know how the "official" factory numbers were derived. I also believe it may have something to do with where the belt rides within the pulley, etc.....

- Wil
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Old 12-05-2006, 12:34 PM
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Just wanted to say thanks to all who contributed and offer some additional information. The smaller 226mm fan & housing does not use a different sized shroud. I bought a 245mm fan housing from an '85 3.2 engine and my '79 SC shroud fits over it just fine. The difference in the fan housing is apparently the inner dimensions. Outer dimensions are the same in my experience of comparing the '79 housing to the '85 and also an '87.
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Old 10-17-2011, 09:42 AM
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KTL:
It depends .

If you are using the 226 mm aluminum fan housing from a 78-9 then the standard shrouding will fit just fine.

If you happen to get a 226 mm magnesium fan housing from a race car, then it does have a smaller OD and reqiure a smaller than standard shroud.

That said, I have seen an aluminum small OD fan housing.... just once.

t
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Old 10-17-2011, 11:29 AM
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tadd,

Good point about the rare factory racing fans. Forgot about those.....

But I have to believe that my instance is true for all the 78-79 street production fans. That being the housing OD is the same, 226 vs. 245, and the ID changes accordingly to handle the fan size.

I think you mixed Al and Mg? The production housings are Mg and the racing ones are Al, correct? Information i've found says all the production housings are Mg except the early (1965-66) 250mm Al ones.
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Old 10-17-2011, 05:44 PM
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Ktl:
The production 245 mm fans and housings are magnesium. The small 78/79 SC fans and housings are aluminum. I've got a set just waiting for enough nickels to fall out of the couch to get that fancy ceramic coating so it looks like mag.

Yes, all the street stuff is the same OD. The racing 226 fan isn't too hard to find. The matching small OD mag housing is getting hens teeth. The 78/79 housing is getting harder to find (undamaged) as well.

Almost all the racing stuff was mag, although aluminum was in voge after the 74 RSR to handle all the power of the turbo cars. The mag case on the 2.1 turbo was only good for 5-6 hours at 500 HP. Porsche made some dimensionally correct 7R cases in aluminum before the 3.0.... Even aluminum chain boxes with center lube (with no boss for the pitersburg fuel pumps like the early cars).

tadd
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Old 10-17-2011, 06:06 PM
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