5 blade vs 11 blade 911 fan

[Martice]

Hi,

Which are the differences in performance between the 5 blade Porsche 911 fan and the 11 blade?
I am in a search for a porsche fan and will be using it on a 2.0L type 4 engine.Overcooling is one thing I am affraid of.Next is hp "stealing" 911 fan vs t1 upright fan.
Any info would help.

Martin

[Alex]

The 5 blade fan provides the most air of all Porsche fans if I am not mistaken, so if you are concerned you should get the 11 blade fan.

Alex

[Farmer]

There is a little difference in how much air they move, but not much. Thewre is, however great difference in at what speed they do things. The 5 blade fan originally came from a Carrera engine and was deigned to spin fast. When Porsche made the newer model engine they then developed the 11 blade fan and lowered the ratio from about 1,7 - 1 down to 1,4, and 1,2 - 1 depending on which engine you look at . The 5 blade has a "cool whining" to it if you like that. no one with a little gas in their blood will be in doubt of what is in there if you rev it. Where as the 11 blade is a little more "silent"
As for overcooling, well you have to do a little trial and error testing to find the perfect compination on your setup. But start with a known factor and work your way out from there.
With a 5 blade on a not too fast reving T4, I would say that 1,6 - 1 would be a good place to start.

Martin, Did you get my mail ?

[Martice]

Thanks guys! I'll come with more question later, after I'll see what options I have.

Torben, got your mail, sent you one :)

regards,

Martin

[Tony Z]

exactly what do you mean by HP stealing 911 fan?? The Porsche fan is about 30% more efficient than the T1 fan, meaning it can move 30% more air for the same power loss or use 30% less power to move the same air.

When I eventually run a dry sump setup, I will go for a power pulley and a porsche fan to keep the stock amount of cooling

[Martice]

If i remember right, the porsche fan moves more air at the loss of power, not because its better design.
You mean that if it spins at a lower rate, it will cool the same as a t1 fan and steal less hp?
Of course, we are talking generic issues here.
Martin

[Tony Z]

I looked into this about 4 years ago, so I cant remember the actual figures.

A fans efficiency is rated in how much "air power" it produces to the amount of mechanical power used.

If I get the time over the next week I will look it up again and let you know. But I do remember that the porsche fan had at least 30% better efficiency than the stock T1 setup.

Also, even though certain fans are less efficient than oters, they work better in certain applications.

[Martice]

Thanks Tony!

I am looking forward to any info.

Martin

[Tony Z]

OK, well, I was wrong about the 30% efficiency. I can’t find too much at the moment, but will try and find more if possible.

Here is what I got:
Multivane centrifugal 50-60 % efficiency. Advantages: Low peripheral speed, quite and compact. Disadvantages: Severely rising power characteristic requires large motor margin. Applications: All low and medium pressure atmospheric air and ventilation plants (air conditioners)

Backwards inclined centrifugal. 65 – 75% efficiency. Advantages: good efficiency. Non-overloading power characteristics. Disadvantages: High peripheral speed. Much louder than multivane centrifugal. Applications: Medium and high pressure applications.

Axial Flow (Porsche fan – 8 tip fan) 60 – 75 % efficiency. Advantages: Very compact, straight through flow, suitable for installation in any position. Disadvantages: High tip speed and sound level – slightly less severe for fan with guide vanes. Low pressure. Applications: Low pressure atmospheric air applications and large ventilation schemes such as tunnel ventilation.


A few things come to mind while I write this, especially the basic hydraulic theory of: high pressure = low volume and low pressure = high volume. Think of it this way. Hold a water hose pipe in your hand. Cover 90% of the open side, the water flies out at high speed (high pressure) and travels a long way, however it is a fine spray with very little quantity. Now open the hole again, the water lands almost by your feet (low pressure) but soon floods the local area to an extent much greater than the fine spray (high pressure).

The Flat 4 engine design does not provide much resistance to flow (many cooling vane openings), so in my opinion, a medium pressure fan is not ideal. The way that our engines cool is through high air flow over the fins. Low pressure = high volume.

If a fan, as with any pump, does not work within its design criteria, it will loose efficiency – it will still work, but not as well.

Also, the Porsche fan was used to cool a 3.6l 6 cylinder. If it didn’t work, they would have used the best fan for the application. Also, with the efficiency advantage, all things the same, you still get more air flow for the same amount of power used.

[Ephry73]

Ok, hate to add gas to the fire, but with a 2,366cc engine the ratio for the pulleys would be recommended as 1.6:1 between crank and fan pulley?

This engine is getting more real as the days go by. I just got a 5blade fan not too long ago, and gathering the parts slowly. Still trying to figure the carbs though and the exhaust



E

[Tony Z]

Well, just to try and add a few cents worth. I am not rreally thinking at the moment, just writing whatever comes to mind, so dont moan if it is a load of hogwash.

Exactly how can you overcool a aircooled engine with a porsche fan. Ok, I understand that the oil has to get to operating temp, but isnt the stock oil cooler removed to make space for the porsche fan. So if that is the case, the operating temp of the oil is governed by a remote cooler. If you end up making the barrels and heads really cold, is that going to make much difference, not like it will shrink to the point where your assembly tolerances will become zero and things start to sieze -or am I wrong? Think about it. There is always combustion happening, so the insides of the cylinders will still be warm.
Oil also starts to break down at temps above 90deg C (maybe higher for automotive oils, cont find any specs), so the cooler the cylinder, the longer the oil will last. The temp of the piston wont change that much, as it is mostly cooled by splashed oil and it is heated by the combustion.

Dont know what you guys think or know, but I am open to suggestions, ideas and arguments - lets wake this forum up!!!

[Alex]

I will add some infos when I am back from Germany.
I have some very interesting infos on the Porsche fans and will write my article as soon as I find the time to do it.


Aöex

[kdanie]

TonyZ, You can overcool an engine, if the pistons/cylinders/heads are too cool you get inefficent combustion, fuel washdown, incorrect running clearances. It's all a balancing act to get the engine to run it's best.

Jake has run dyno tests with the same engine swapping out a 911 fan/shroud for a type 1 DTM style fan/shroud and found the 911 system consumed more HP and did not cool as well! Back to back tests on a dyno don't lie.

If someone really wants to run a 911 shroud it should be because of the "cool factor" not for extra cooling capacity and understand that they would make a little more power with a type 1 system. Am I down on 911 systems? Absolutly not, that's what is on my engine but I know the trade offs.

I have an 11 blade fan with a 1-1 drive ratio. I have coated the cylinders and heads with a high tech heat sheading coating and the piston tops, combustion chambers, and valve heads with ceramic coating to contain the heat in the combustion process. The compression ratio is set at 10-1. I live in an area that gets pretty hot in the summer, 90-100 degrees. I hope I have achieved an effective balance between heat generation and cooling capacity.
ken

[Ephry73]

Tonyz, I understand your point, but I also know(from reading and hearing guys on these forums) that the oil needs to reach an "operating" temperature to burn off any water, and to burn off any "dirt" in it. I figure that with a remote cooler, and a thermostat set at around 180* F the engine should run ok. I was planning on running the CR high, and making sure that all of the components are matched....

Another thing I want to do is have everythnig throuroghly checked and balanced, as to avoid any friction.....



E

[zynnad]

would you have to get a smaller pulley in order to find the right setting for the fan? or vise versa ...get a bigger pulley?

[kdanie]

My 911 kit came with a 1.6-1 crank pulley, I bought a smaller pulley from Fat Performacne that is 1-1.
ken

[Alex]

For your info:

Latest dyno test showed that the fan took 6hp on Zen's engine.
If you get a pulley with a 1:1 ratio the Porsche shroud will NOT work that well.

Please wait a week or two.....I have some really good infos for my article.

Alex

[Tony Z]

Just picked up 11 blade fan kit, all for $320. Not bad hey?? Dry sump here we come, just gotta get the cash to finish the 2332 and it can all be installed

[Oliver Knuf]

For sure you have to interchange pulley-diameters, just to get the correct ratio.

A safe thing, to be warned, that the diameter is too small is, if the generator light comes on! LOL


5 blades for president! 12 blades are good, but...! 11 blades provide best airflow, besides it's less noisy than the 5 blades! Problematic is, that you can't get the 11 blades new.

[fast70]

So there is no real problem running a 5-blade fan? I am having a hard time locating an 11-blade fan. Would it cause any problems or should I keep looking for an 11-blade?

Thanks,
fast70

[Tony Z]

Think about it this way, the 5, 11 or 12 blade was designed to cool a lot more power, cylinders, boost and heat than we will ever need.

The only problem with running a 5 blade fan that I can think of is as follows.

I dont like the look. Yes, if nothing else was available, I would run a 5 blade (almost did too), in all honesty, I REALLY REALLY REALLY REALLY like the 12 blade, but those cant be found in SA, so I opted with the 11 blade.

It all boils down to looks!!! They each have their specific design application, which is much more than we need anyway.

[fast70]

Yeah,
I don't know what I was thinking! As if the fan for a 6-cyl would'nt be good enough for a 4-cyl. Thanks for showing me the logic!

Thanks,
fast70

[Split50]

The 5 blade fan was introduced to the 2.7 911 in the mid 70's to make the engine run hotter in order to reduce exhaust emissions.
How do I know? I have a mid 70's 911 and every thing I have read about it tells me to upgrade to the 11 blade fan before the engine overheats and pulls the head studs out of the case.
So the 5 blade fan cools less.
To confuse things even more there were 2 sizes of pulley too.

Tim

[fast70]

Yeah,

I think I read that in a Porsche manual once. They did it in order to reduce emissions by making it run hotter.

fast70